Log In  


I felt like transcribing a little tune I made in Caustic to Pico8.
Could use a bit more work (instruments, balancing, is pattern 14 off key?) but I'm happy enough with it.

P#82002 2020-09-20 04:27 ( Edited 2020-09-20 04:27)

by Mot
Cart #mot_pool-19 | 2020-09-21 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

A work-in-progress 3D pool table simulation.
AI is still quite unfinished.

P#81393 2020-08-31 11:55 ( Edited 2020-09-21 09:31)

Not sure if anyone has posted a smap() yet, but it's reasonably straightforward to implement with tline, so here's mine.

Parameters are:
cx,cy,cw,ch Specify a region in the tile map. Measured in tiles.
sx,sy,sw,sh Region on the screen to map to.
flipx,flipy Whether to flip horizontally and/or vertically.
layers Layer flags. Same as for map().

You need to supply at least the c and s parameters.

function smap(cx,cy,cw,ch,sx,sy,sw,sh,flipx,flipy,layers)

 -- negative screen sizes
 if(sw<0)flipx=not flipx sx+=sw
 if(sh<0)flipy=not flipy sy+=sh

 -- delta
 local dx,dy=cw/sw,ch/sh

 -- apply flip
 if flipx then
 if flipy then

 -- clip
 if(sx<0)cx-=sx*dx sx=0
 if(sy<0)cy-=sy*dy sy=0

 -- render with tlines
 -- pick direction that results
 -- in fewest tline calls
 if sh<sw then
  -- horizontal lines
  for y=sy,sy+sh-1 do
  -- vertical lines
  for x=sx,sx+sw-1 do

Cart #mot_smap-0 | 2020-07-22 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

P#79752 2020-07-22 05:44

Mot's Animation System

Cart #mot_animsys-2 | 2020-07-19 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Mot's Animation System is a visual editor for creating 2D animations.

You start by sequencing sprites and/or tilemaps together to create the basic components. Then combine them using timelines and key-frames to make animations. Or combine them again to make bigger, more complex animations.

Animations can trigger sounds and music, and call back into to your main program, e.g. to trigger game play events.

You could use it for:

  • Character animations, like run cycles
  • Larger multi-sprite animated characters
  • Cutscenes
  • Animated birthday cards

Animations can be loaded and played in your own carts (the loading and playback code is 1836 tokens). They can either be stored in Lua strings or loaded from a separate cart.


This is all very much in Beta at the moment!. And some corners had to be cut to fit everything into the token limit. In particular the editor doesn't prevent you from shooting yourself in the foot by:

  • Creating self referencing animations (infinite recursion)
  • Creating animation files larger than 0x4300 bytes (about 17K) that won't save properly.

It lacks any sort of undo/redo logic, so if you use this, please take frequent backups of your saved animations.

And also, because the animation code is 1836 tokens and the animation data can be several kilobytes, it's not the best fit for every program.

Feel free to @ me if you need any help.

Overview and basic navigation

WARNING: While you can edit animations in the nested browser version you can't save them! So please don't get too invested if you play with it in-browser. Run it from Pico-8 itself in order to save your changes.

Selecting and playing animations

Move the mouse over the window to display the UI.

You can pan the animation with the middle mouse button, and zoom in/out with the scroll wheel.
At the bottom right there are 3 controls:

  • A slider to zoom in/out (behaves exactly the same as the mouse wheel)
  • A play/pause button that does what you'd expect
  • A home (house) button recenters the animation and sets the scale back to 1

The name of the current animation is displayed at the top. Click on it to select another animation.

Use the mouse wheel to scroll through the animations. Animations with a person icon are sprite/tilemap animations. Animations with a dotted line icon are key frame based animations.


At the top right are the menu icons. Clicking on them opens a drop down menu.

The hamburger menu is for creating/deleting animations.

You can create new animations of different types, or delete the current animation.

The hourglass menu is for saving and loading animation sets.

You can save/load your animations to from external carts or import sprites and tilemaps from another cart.

This is covered in more detail later.

Animation properties

Click "Properties" at the bottom of the screen to expand the properties panel.
This is where you edit the current animation. The UI changes based on the animation type.

When expanded, the "Properties" bar also displays two icons. These toggle between different tabs.
The I icon displays information and settings for the animation. Once again they differ based on the animation type. The other icon will be the person or dotted line depending on the animation type, and switches back to the main editor.

Creating animations

Importing graphics

(...and music and sound effects)

In order to create animations for your own carts, you'll want to import the sprites and tilemaps that your cart uses.
Click the hourglass icon at the top right, then select "IMPORT GFX". This will list the carts in your Pico-8 carts folder.

Once again you can scroll with the mouse wheel.
Click on the cart to import its sprites, tile maps, sound effects and music into the editor.

Clearing animations

Select "Clear" from the hourglass menu to clear out the demo animations.

Saving and loading

The hourglass menu allows you to save and load your animations. Animations are saved to Pico-8 cartridges ("carts").
They overwrite the sprites in the cart, and possibly the tile maps, sfx and music, depending on how many animations you have defined. Therefore you should not save your animations into your existing game carts!

To avoid catastrophe the editor will only save/load animation data into cart files that end with .anim.p8

"Save", "Save as" and "Load" work as you would expect.

The first time you save (or if you click "Save as") you will be prompted with a list of animation carts to save into.

Or you can click "New Cart" and key in the name of a new cart to create.

Enter the name without the .p8 extension, as the editor will add .anim.p8 automatically.

WARNING: The editor can only save 0x4300 bytes of animation data to a cart (about 17K). If your animations grow beyond this limit, they will not save correctly and may not reload either.
You can keep tabs on this by running Pico-8 in console mode. The number of bytes written is reported in the console when you save, so you can see when it gets near the 17K limit (for reference, the demo animation is about 3.8K).
Taking frequent backups of your animation file is strongly advised.

Sprite animations

Sprite (and tile map) animations are the building blocks of all animated sequences.
Create a sprite animation by clicking the hamburger icon and selecting "NEW SPRITE ANIM".
To edit the animation, make sure the "Properties" section is expanded.

This UI allows you to define a sequence of frames, each of which displays a sprite.
The frames of the animation are displayed horizontally.

Click on a frame to select it.
If the animation has more than 5 frames, click the rightmost frame to scroll right and the leftmost to scroll left.

The "+" and "-" buttons add and delete frames respectively. Adding always creates a new frame at the end of the animation. Alternatively you can insert a new frame immediately after the selected frame by clicking "Ins".

The bottom of the editor shows the available sprites.

As in Pico-8 itself, sprites are grouped into 4 pages, with page number "tabs" at the top right.
To set the sprite for a particular frame, first click on the frame, and then click on the sprite in the sprites area.
The sprite for the current frame is displayed with a white rectangle.

You can also flip a frame horizontally or vertically by ticking "Flip X" and "Flip Y" respectively while the frame is selected.

Information and settings

Click the I icon on the "Properties" bar to display the sprite animation information and settings.

The Name allows you to give your animation a name, so you can find it more easily in the animation chooser.
You should try to choose short names in order to save space and so that they display properly in the animation list. (Ideally the editor would enforce this but it doesn't have enough spare tokens.)
The name is also used to fetch animations when rendering them in your own carts, so it is a good idea to give each animation a unique one.

The Type allows you to choose between a sprite or tile map based animation. (Tile map animations are described in the next section.)

FPS is the frames-per-second speed of the animation.
The value is set using a "number editor" box. Click and drag left/right to decrease/increase the value. Click and drag with the right mouse button to decrease/increase 10x faster.

Size is the horizontal (left box) and vertical (right box) size of each frame in sprites (or tile map tiles, if using a tile map animation).

The Origin defines the origin point of the animation. If the animation is rendered at coordinates X,Y then the origin is the part of the animation that will align with that position on screen. It is also the part of the animation that stays in the same place if you scale it larger or smaller. It's stored as two values ranging from 0 to 1, representing the fraction of the animation's width and height. So (0,0) sets the top left corner as the origin. (1,1) sets the bottom right corner. (0.5,0.5) sets the center.

Hover the mouse over the animation preview area to see the origin point (displayed as a gray cross)

Tile map animations

Tile map animations are special sub class of sprite animations, where the animation frames are defined as sections of the tile map. They are useful for creating larger "sprite" animations, or to define backgrounds for animated scenes.

To create a tile map animation, first create a sprite animation (as described above), click the I to bring up the information/settings and click "Tiles".
Typically you will want to set "Size" here as well (to the width and height of the animation in tiles).

Click the person icon to edit the tile map frames.

The UI is similar to defining sprite frames UI. The main difference is that the tile map is displayed instead of the sprite pages. Use the middle mouse button to drag the tile map around, so that you can select the region that corresponds to your animation frame.

(The UI is unfortunately a bit cumbersome and would have benefited from a mouse-wheel zoom. But it's usable.)

Timeline animations

This is the main feature of the animation system: the ability to create animations defined by key frames on a timeline.
Timeline animations are built from other animations, which are often sprite animations but can be other timeline animations as well. In this section we will refer to the other animations as "child animations".
The key frames specify which animations to play at which positions, plus other attributes like scale and flip flags. The animation system interpolates between these values based to create the animation.

Create a timeline animation by clicking the hamburger icon and selecting "NEW TIMELINE ANIM".

The timeline animation UI has two main areas.

Timelines and key frames

The left area contains the timelines and key frames.

The blue top line is for triggering events, like sound effects. This is covered later on.

The gray lines are timelines. Each one displays a single "child" animation. You can include more child animations by creating more timelines, using the buttons at the bottom.

The + and - buttons add and delete timelines respectively.
Use the up and down arrows to re-order the timelines. This controls the order that the child animations are drawn on screen. Timelines are drawn from top to bottom, so the topmost timeline's animation will appear behind the others, and the bottom timeline's animation will appear in front.

The purple dots on the timeline are key frames.
These can be added and deleted with the key frame buttons:

To insert a key frame, first click on the timeline at the position corresponding to the desired time. Then click +.
Note: If key frames are close together it may be difficult or impossible to click on the timeline between them without selecting one of the existing ones. The work around is to click + to create the new key frame anyway, then move it to the desired time.

To delete a key frame, click on it to select it, then click -.

Key frame properties

The right hand side displays the properties of the selected key frame.

Use the number box at the top to set the key frame time on the timeline (drag left/right with the mouse).
(I would have preferred to implement this as dragging the key frame along the timeline, but you know... tokens.)

The key frame properties are grouped into two tabs, which are accesed by clicking the icons to the right of the number box.

The first tab () has the following properties:

Anm selects which child animation to play. Click on the animation name to select it from the list. The child animation will play from this key frame onward. If "None" is selected, the key frame will not change the child animation.

Loop indicates whether the child animation will loop. If not it will stop once it has played to the end (or start if playing backwards).

T and Spd set the time and speed of the child animation. You can use these to start the child animation half way through, or play it in reverse, or double speed etc.
T and Spd are optional properties. This means you can choose not to specify them on a particular key frame, which is useful if you want to add a key frame to change a different property (say the on-screen position). Optional properties are controlled by a tick box on the right hand side which must be ticked in order to enter a value.
For T and Spd there is only one tick box, as you must either set them both, or none at all.

Visible indicates whether the child animation is visible from this key frame onward.

Click the icon to display the second tab.

It has the following properties:

Pos sets the position of the child animation as a X and Y coordinates, relative to the center of the current time line animation. If you render the animation in the center of the screen (like the editor does by default), then 0,0 will position the child animation there.
Pos is an optional property.
It is also an interpolated property. As the animation plays the position will be linearly interpolated between the values supplied on the key frames, so that the child animation moves smoothly from one position to the next.

Sca sets the horizontal and vertical scale factor of the child animation. A value of 1 means no scaling.
Sca is an optional interpolated property.

Flp flips the child animation horizontally and/or vertically from the current key frame onward.

Note: The Visible property is also available on this tab page. It is the same property as on the other page.

Information and settings

As with sprite animations you can click the I icon to display the information and settings.

Refer to the sprite animation section regarding the Name property.

The Duration allows you to specify the animation duration in seconds.

Storyboard animations

A storyboard animation allows you to play a set of animations one after the other. It is useful for stitching together smaller scenes, like the scenes that make up the demo animation. The editor ensures that each animation starts immediately after the previous one finishes, and adjusts it appropriately in response to duration changes.

To create a storyboard animation, click the hamburger icon and select "NEW STORYBOARD ICON".

The storyboard animation UI is essentially a cut down version of the timeline animation UI.There is no events timeline and only one animation timeline, and key frames are restricted to a subset of properties.

Create the storyboard by adding key frames to the single timeline and setting the "Anm" property to the animation that should play.

Unlike timeline animations, you cannot set the key frame time directly. Instead there are two new key frame buttons that allow you to control their order.

Click the left button to move the key frame to towards the start of the sequence. The right button moves it towards the end.

Animation events

Timeline animations can also trigger events. These can be used to play sound effects and music, or display text on the screen. You can also create your own event types and handle them in your own carts.

Events are created by inserting key frames into the blue top-most timeline.

The Typ property specifies the event type.
The remaining properties are data to supply to the event handler. If an event handler doesn't use a particular property, you can choose to omit it by leaving its right-hand tick-box unticked (which saves a byte or two in the animation data).

Click on the value to select the event type.

The editor displays the built-in event types that it understands. Or you can click "Custom" to create your own event type. Custom event types are ignored by the editor, but you can implement event handlers in your own carts (this is described later on).
You should keep your custom event names short, as the name string is stored in each event.

The built-in events are as follows:

SFX plays a sound effect.
n=The sound effect number.

MUS starts/stops music.
n=The starting pattern. Omitting it (unticking the right tick-box) indicates that the music should stop.

TXT displays text on the screen.
txt=The text to display
pos=The screen coordinates
n=The number of frames the text will remain on screen

RELTXT displays text on screen relative to the current animation.
This is exactly the same as TXT except that "pos" is relative to the center of the current animation.

CLR clears all text from the screen.

Playing animations in your own carts

Loading and playback code

In order to load and playback animations from your own carts, you will need the loading and playback code.
All this code is in tab 1 of the "Mot's Animation System" cart, and needs to be copied into your cart. Be aware that it will cost you 1836 tokens.

Loading from an external cart

Loading animations from an external cart means that your cart will not be self-contained, and may prevent it from working when uploaded onto the Lexaloffle BBS. However it's relatively easy to setup, and makes for a streamlined workflow, where you save your changes in the editor and simply rerun your cart to load them.

You might want to use this method while developing your cart, and then switch to the embedded Lua string method (described later) once you're ready to release it.

To load from an external cart:

    -- load into gfx ram, then decode
    local stream=readmemstream(0x0)

    -- restore gfx ram

    -- extract animation to play    

This copies the animation data into memory, and deserializes it into a Lua table.
The process overwrites the sprites and possible tile maps, sfx and music, so the "reload" is necessary to copy them back in from the cartridge ROM.
Individual animations can then be fetched by name.

Rendering an animation

To render an animation, call the "draw" method:


Where t is the animation time in seconds.

By default the animation will not loop, but you can use the "duration" method to achieve this if necessary.


The full list of parameters for "draw" is:
t=The animation time
x,y=The position on screen (defaults to 64,64)
xscale,yscale=The horizontal and vertical scale factors (defaults to 1,1)
flipx,flipy=Whether to flip horizontally or vertically (defaults to false,false)
dt=The delta time from the last frame (defaults to 1/30 or 1/60 depending on whether _update or _update60 is defined)

The delta time is used to trigger events, and tells the animation system how far the animation has advanced since the previous frame. The animation system will trigger all events on the timeline between then and the specified time.

Drawing text

If an animation contains "txt" or "reltxt" events, this text is not rendered immediately by the "draw" method, but queued up to be rendered later. This this allows you to render one or more animations then draw the text last so that it appears in front.

After drawing your animations, render the text by calling the "framedone" method of the "anim_events" global variable:


Handling animation events

When an animation event triggers, the animation system looks for a function on the "anim_events" global variable with the same name as the event to call.
The system sets up a default "anim_events" table with handlers for the built-in events ("sfx","mus","txt","reltxt","clr"), so these events will work automatically.

You can handle your own events by adding functions to the anim_events table.

The parameters are:

ev=The event key frame.
This is a table variable with properties:

  • t
  • x,y
  • n
  • txt

Which correspond to the values configured in the animation editor. Property values (except t) can be nil if no value was entered.

x,y=The screen position of the animation that triggered the event.

Note: To save tokens the event is called as a function, not a method. I.e. there is no "self" parameter.

After frame rendering

You can also create event types that render content after the animations have been rendered (like the "txt" and "reltxt" events), by calling anim_events.doafterframe and passing it a function to run.
The function will be converted into a coroutine, so you can use yield() for multi-frame drawing.

For example, here's an event that causes the screen to flash 3 times. The screen will flash white by default, or you can specify a colour by setting "n":


   -- three flashes
   for i=1,3 do
    -- one frame of white
    cls(ev.n or 7)

    -- two normal frames

Embedding animations as Lua strings

Instead of loading animation data from an external cart, you can embed it directly into your Lua source as hexidecimal strings, to create a single self-contained cart.

For example, here's the demo animation embedded into a cart as a Lua string:

Cart #mot_animintro-1 | 2020-07-19 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

You will need enough free space to fit the strings in without exceeding the compressed size limit however.

To generate the Lua strings you must run Pico-8 in console mode.
Load your animation in the editor, then click the hamburger icon and select "EXPORT ANIMS".

The editor will write a table of hexidecimal strings to the console window. This looks like (on Windows anyway):

INFO:  "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",
INFO:  "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",
INFO:  "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",
INFO:  "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",
INFO:  "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",
INFO:  "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",
INFO:  "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",
INFO:  "0100000b3900000000000064000c0100000b365b001500000064000c0100000b1945000a00000064000c0100000b1954000a00140064000c0100000b1965000a000a0064000c00020774722d6d616b65f000010100000b320000000054019cff0400020974722d706c7466726de803020100000b160000f9ff000064000c0100000b1800000000000064000c00020974722d736d6f6b65326400010200000b170000000000006400046400020000ebff0400020974722d736d6f6b65336400040100000b3700000000000064000c0100000b37000000001e0064000c0100000b37000000003c0064000c0100000b3700000000500064000c00020874722d747261696e6400010100000b3200000000000064000c00",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  "",
INFO:  ""}

You will need to copy it from the console window and remove the "INFO: " line prefixes. You can optionally remove any blank strings at the end of the table.

Then add it to your code, assigning it to a variable. For example:


You can now use the following code to load the animations:

    -- load animation from animdata string
    local stream=readstrstream(animdata)

    -- extract animation to play    

P#79085 2020-07-12 00:44 ( Edited 2020-07-19 06:57)

OK, this may be a bit bonkers, but I figured out how to play Ramps with a racing wheel, with proper analogue steering and acceleration/braking.

It's a little involved and only works on Windows.

Mouse input

First, you need a version of Ramps (or whatever game you plan to play) edited to accept mouse input. Like this version:

Cart #mot_ramps_mouse-0 | 2020-06-06 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

WARNING: Attempting to drive with an actual mouse may cause high blood pressure and throwing things.
Also I've only tried this in PICO-8 itself - not sure if it works when running in a browser.

Joystick -> mouse

Next, you need a utility to convert game controller input to mouse movement.

I couldn't find one that did exactly what I needed, so I ended up making my own here.
Tip: If you try it out remember F12 toggles it on/off - as you can't use the mouse when it's enabled.


So basically run the utility, run the mouse-input version of Ramps in PICO-8, switch to full-screen, and go :-)

P#77721 2020-06-06 01:58

I'm a bit new here, so I don't know if adding network capability has previously been discussed (?)

But it feels to me some simple UDP send/receive instructions would add some cool functionality, without adding too much complexity.

Perhaps something like:

[write message to RAM]

Where [ip-locn],[port-locn] would be some special reserved locations for IP address and port.
UDP packets are usually small. I've seen <=512 bytes recommended in places, which easily fits into the user RAM address range.
And an IPV4 address would fit in a number variable, and would be adequate for LAN play.

Receive could be:

[read message from RAM]

Returning 0 if nothing is waiting.
It could also populate [ip-locn] with the return IP address so that replying would be straightforward.

Perhaps [port-locn] could be pre-populated with a default port number (0x1C08 ?).

Any thoughts?
Am I trying to make it simpler than is actually possible? (I haven't done socket programming in a while, so I forget what's necessary to get UDP/IP working).

P#77688 2020-06-05 09:36


by Mot
Cart #mot_ramps-21 | 2020-06-22 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This is Ramps! A 3D racer inspired by Powerdrift, Stunt Car Racer, Hard Drivin'.

Choose from 8 varied race tracks, and overtake the other drivers in 5 laps to win.
As well as racing you'll need to navigate jumps, roller-coaster like ramps and occasionally even drive upside down.

Includes 3 difficulty levels, plus a practice mode for getting the feel of the tracks.

This all started as an experiment to see how well Pico-8 could render a Powerdrift-like scaled sprite racetrack (pretty well, as it turns out). Then it was about trying to implement a driving model that could handle the ramps, jumps and loops. And finally wrapping it up into a somewhat finished game.

Like with Loose Gravel, I would have liked to add a championship mode, but there just aren't enough tokens :-)

Big thanks to everybody who gave advice and feedback. Particularly @freds72 who even went as far as digging into the code and making some performance optimisations (~20% CPU improvement!).


Z = Accelerate
X = Brake
Left/Right to steer

You don't have to wait to be automatically respawned after you fall of the track, select "Respawn" in the pause menu to get back into the race faster.

The green and red lines on the speedometer are recommended minimum and maximum speeds.
The green line (minimum speed) is particularly important for clearing jumps (and occasionally getting up steep hills), so make sure to keep your speed above it.
The red line (maximum speed) is to prevent you from sliding out on sharp corners or overshooting the jumps. Typically this is just a suggested speed. Depending on your racing line, driving style etc you may be able to go faster.


Update: Other cars' speeds now vary randomly throughout the race
Update 2: Can knock other cars sideways a bit & they don't knock you sideways as much. Round road sprite corners a bit.
Update 3: Fix game crashes in AI code when road is blocked.

P#77443 2020-05-31 05:23 ( Edited 2020-06-22 08:03)

Instant 3D plus!

Instant 3D! was a random idea, quickly thrown together to see if it was possible. But after seeing the cool things people can do with it, I wanted to clean it up properly, and also present some of the internal functions more cleanly.

Making the 3D functions more accessible means:

  1. You can often get your game working correctly in 3D even if the Instant 3D "magic" doesn't work correctly, by calling the 3D spr/map functions directly with the right parameters.
  2. You can do things that the original Instant 3D can't do, like having objects that hover into the air.

I've added a little tutorial of converting a 2D game to 3D to illustrate how this works, at the bottom of this post.

Obviously this "snippet" is still very limited, compared to a general purpose 3D library say. You can't use it to create an FPS or a flight simulator. But I think it's a lot easier to use - start with a 2D game, drop it in, and fix up the bits that don't come out right. And you can still do some cool looking 3D stuff with it.

Here's the updated snippet:

-- instant 3d+!

 -- parameters
  vanish={x=64,y=0}, -- vanishing pt
  d=128,             -- screen dist in pixels
  near=1,            -- near plane z
  camyoff=32,        -- added to cam y pos
  camheight=32       -- camera height

 -- save 2d versions

 -- 3d camera position
 local cam={x=0,y=0,z=0}

 -- is 3d mode enabled?

 -- helper functions

 -- screen to camera space
 local function s2c(x,y,z)
  return x-cam.x,y-cam.y,z-cam.z

 -- perspective projection
 local function proj(x,y,z)
  if -y>=p3d.near then
   local scale=p3d.d/-y
   return x*scale+p3d.vanish.x,-z*scale+p3d.vanish.y,scale

 -- screen to projected
 local function s2p(x,y,z)
  local x,y,z=s2c(x,y,z)
  return proj(x,y,z)

 -- 3d drawing fns
 function sspr3d(sx,sy,sw,sh,x,y,z,w,h,fx,fy)
  w=w or sw
  h=h or sh
  local px,py,scale=s2p(x,y,z)

  if(not scale)return
  local pw,ph=w*scale,h*scale

  -- sub pixel stuff
  local x0,x1=flr(px),flr(px+pw)
  local y0,y1=flr(py),flr(py+ph)

  if(not z)return
  -- convert to equivalent sspr() call
  w=(w or 1)*8
  h=(h or 1)*8
  local sx,sy=flr(n%16)*8,flr(n/16)*8

 function map3d(cx,cy,x,y,z,w,h,lyr)
  if(not h)return

  -- near/far corners
  local fx,fy,fz=s2c(x,y,z)
  local nx,ny,nz=s2c(x,y+h*8,z)

  -- clip

  -- project
  local npx,npy,nscale=proj(nx,ny,nz)
  local fpx,fpy,fscale=proj(fx,fy,fz)

  if npy<fpy then
   local tx,ty,ts=npx,npy,nscale

  -- clamp

  -- rasterise
  local py=flr(npy)
  while py>=fpy do

   -- floor plane intercept
   local g=(py-p3d.vanish.y)/p3d.d
   local d=-nz/g  

   -- map coords
   local mx,my=cx,(-fy-d)/8+cy

   -- project to get left/right
   local lpx,lpy,lscale=proj(nx,-d,nz)
   local rpx,rpy,rscale=proj(nx+w*8,-d,nz)

   -- delta x
   local dx=w/(rpx-lpx)

   -- sub-pixel correction
   local l,r=flr(lpx+0.5)+1,flr(rpx+0.5)

   -- render


 function map3dupright(cx,cy,x,y,z,w,h,lyr)
  if(not h)return
  local px,py,scale=s2p(x,y,z)
  if(not scale)return

  local pw,ph=w*8*scale,h*8*scale

  -- texture step
  local dx,dy=w/pw,h/ph
  local mx,my=cx+0.0625,cy+0.0625

  -- sub pixel stuff
  local x0,x1=flr(px),flr(px+pw)
  local y0,y1=flr(py),flr(py+ph)

  if(x0>=x1 or y0>=y1)return

  for y=y0,y1-1 do

 function camera3d(x,y,z)

 -- "instant 3d" wrapper functions
 local function icamera(x,y)
  cam.x=(x or 0)+64
  cam.y=(y or 0)+128+p3d.camyoff

 local function isspr(sx,sy,sw,sh,x,y,w,h,fx,fy)
  z=h or sh

 local function ispr(n,x,y,w,h,fx,fy)
  z=(h or 1)*8

 local function imap(cx,cy,x,y,w,h,lyr)
  cx=cx or 0
  cy=cy or 0
  x=x or 0
  y=y or 0
  w=w or 128
  h=h or 64

 function go3d()

 function go2d()

 -- defaults

-- enable 3d mode

As before, to use it, just copy it into your 2D program. It should behave exactly the same.
There's one new feature, in that you can toggle between 2D and 3D in the Pico-8 menu.

You can also do it in code using




which might be useful for 2D title screens etc.

Taking it further

The basics are the same as before, but you can now - with a little bit of work - take your games a bit further by making use of explicit 2D and 3D commands, rather than leaving it up to the snippet to guess your intent.

To illustrate this, I made a little 2D cart to convert into 3D.

Cart #instant3dplus-0 | 2020-05-16 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This is a simple little game where you're a bouncing ball that collects coins. It's not finished, but is enough to demonstrate the process. The game is already a little bit 3D in that the ball and coins also have a height, and objects can move in front and behind each other, so it has to sort their positions and draw them from back to front.

Dropping the snippet into this program has... mixed results.

As you can see, it's kind of 3D, but it has some issues:

  • The ball doesn't always bounce straight up. In fact if you look closely it's actually staying on the ground and just bounces away and back again.
  • The coins aren't raised up properly either.
  • The metallic struts are flat on the ground, rather than standing up.
  • Likewise the gratings on top are also flat on the ground.
  • The 3 lives are displayed in the wrong place.

Obviously the snippet doesn't know exactly what we're trying to achieve, but fortunately we can help it out.

With a little bit of work we can make it look like this:

3D functions

We can fix up the ball using an explicit 3D function. The snippet provides explicit 3D functions spr3d, sspr3d and map3d. They have the same parameters as the standard functions, except there's a Z parameter immediately after the X and Y screen parameters.

They use a 3D coordinate system where:

  • The X axis is to the right
  • The Y axis is out of the screen (towards you)
  • The Z axis is up

This keeps X and Y consistent with the "Instant 3D" logic, where instead of moving up the screen as Y decreases, objects move away from you. The new Z parameter allows us to also specify the height.

The ball drawing code looks like this:

  elseif thing.typ=="player" then

The sspr() call draws the shadow, which looks correct already, so it doesn't need to change.
The spr() call draws the ball, based on the thing.x,-.y and -.height variables. The game stores the position of bottom center of the ball, so it has to subtract 4 and 8 to get the top left corner for spr().
We can change it to an explicit 3D call as follows:


We're still specifying the top left corner, but now it's in 3D.

The coin code is similar:

  if thing.typ=="coin" then

Once again we change the spr call to an spr3d:


With 3D positions supplied, the ball and coins now bounce/float above the ground properly.

Upright maps

Next we can address the red metal structs. Currently they are lying flat on the ground instead of standing up straight.
The "instant 3D" snippet assumes everything drawn with "spr"/"sspr" is upright, and everything drawn with "map" is flat on the ground. However the struts are drawn using map(), so that they can be composed of multiple sprites.
So we need to tell the game to draw them upright.

map3d won't help in this case. We can use it to draw them higher up, but they will still be lying flat, not standing upright. So to help with this the snippet provides an alternative "map3dupright" function.

The strut drawing code is:

  elseif thing.typ=="strut" then

We can change the map call to a map3dupright like this:


Once again it has the same parameters as "map", except there's a Z parameter immediately after the X and Y.
The struts are 40 pixels high, so we set the Z (i.e. the height) to 40, to specify the top left corner position.

With this in place, the struts now stand upright.

Cart #instant3dplus-1 | 2020-05-16 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

3D parameters

Now that objects are above the ground they often disappear above the top of the screen.
This is due to the camera height, and the "vanishing point" of the 3D projection, which is currently set to the top of the screen.

We can easily fix this by changing the 3D parameters.
The default parameters are in the snippet:

 -- parameters
  vanish={x=64,y=0}, -- vanishing pt
  d=128,             -- screen dist in pixels
  near=1,            -- near plane z
  camyoff=32,        -- added to cam y pos
  camheight=32       -- camera height

We can move the vanishing point into the center of the screen by adding a line to the _init function:


Moving the vanishing point is like rotating the camera upwards slightly. Now we can easily see everything.
In fact we can even move the camera down a little and nearer to the ball:


3D map coordinates

Now we'll fix the metal grates. These are supposed to sit on top of the struts.
The grates are rendered as a single map, much like the floor. We need to tell the game to draw that map above the ground.

This time map3d is the correct function to use.

The existing code looks like this.

 -- roof map

The 3D code is quite similar:

 -- roof map

Once again we have a new Z parameter after the X and Y, which we set to 40 to move it up into the air.

In the 2D version the grates are drawn last, as because they are above everything. However in the 3D version they actually need to be drawn before the ball, coins and struts to get the correct ordering.
So the line should be moved up immediately after the "map" call that draws the floor.

2D drawing

The last thing to fix is the lives display. Lives are displayed as 3 balls, but they are drawn in the wrong place, because the "instant 3D" logic is trying to position them in 3D.

In this case we really just want to draw them in 2D.

Fortunately the snippet saves the original 2D functions as "spr2d", "sspr2d" and "map2d", so we can call them directly if we need to.

The life drawing code looks like this:

-- overlay
for i=1,player.lives do

Simply change the "spr" to "spr2d" and we're done.

2D/3D code

Adding the various 3D calls makes the game look correct in 3D now. But if you switch it back to 2D (via the pause menu) it now looks broken.

One solution is to simply remove the "menuitem" calls from the snippet and disable mode switching. This is perfectly valid if the game is only supposed to be 3D.

But if you really do want the 2D option, it is still possible. The snippet includes a variable "is3d" which is set to true in 3D mode. Before calling any 3D function, check it to ensure you are actually in 3D mode. If not, perform the original 2D call instead. For example:

if is3d then

Here's the final cart with 2D and 3D mode support.

Cart #instant3dplus-2 | 2020-05-16 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Other bits

That's the gist of how to use it. There are a couple of functions I've missed, like camera3d (sets the 3D camera position explicitly, rather than inferring it from the 2D position and height/y-offset parameters), and a pset3d/pset2d which should do what you'd expect.

Feel free to throw me any questions you have.


** Update 1: Fix spr() when drawing larger than 1x1 sprites

P#76690 2020-05-17 00:58 ( Edited 2020-05-18 23:56)

I often find myself declaring a lot of arrays/object literals that are essentially just data. No computation involved.
For example:

-- background types

It's a useful way to create flexible, extendable systems.

Unfortunately it quickly chews through the token count.

So I was wondering what people's views were of changing the token counting rules around such object literals? - say 1 token per object literal.

They would have to be restricted in order to qualify for a reduced token count, i.e. data only, no computation, functions etc, similar to how JSON is a restricted subset of JavaScript.
The compiler could either detect this automatically, or possibly a new "data only literal" syntax could be introduced.

I feel like this probably aligns with the PICO-8 principals, as it's arguably data rather than code, and you still have the compressed size limit. It seems like a much cleaner solution than the string shredding/JSON parsing workarounds that are currently used.

P#76530 2020-05-14 02:15

Variable inspector window

Debugging carts with "print" and "printh" can be cumbersome, so I made a little snippet to help.
It adds a little window where you can view variables and drill down into them.

To use it, add the snippet somewhere into your program:


    poke(0x5f2d, 1)

    -- watched variables
    local vars,emp={},true

    -- window state
    local exp=false

    -- text cursor
    local x,y

    -- scrollbar
    local sy=0 
    local sdrag

    -- mouse state
    local mx,my,mb,pb,click,mw

    function clicked(x,y,w,h)
        return click and mx>=x and mx<x+w and my>=y and my<y+h

    function butn(txt,x,y,c)
        return clicked(x,y,4,6)

    -- convert value into something easier to traverse and inspect
    function inspect(v,d)
        d=d or 0
        local t=type(v)  
        if t=="table" then
            if(d>5)return "[table]"
            local props={}
            for key,val in pairs(v) do
            return {
        elseif t=="string" then
            return chr(34)..v..chr(34)
        elseif t=="boolean" then
            return v and "true" or "false"
        elseif t=="nil" or t=="function" or t=="thread" then
            return "["..t.."]"
            return ""..v

    function drawvar(var,name)
        if type(var)=="string" then     

            -- expand button
            if(butn(var.expand and "-" or "+",x,y,7))var.expand=not var.expand

            -- name
            print(name,x+4,y,12) y+=6

            -- content
            if var.expand then
                for key,val in pairs(var.props) do

    function copyuistate(src,dst)
        if type(src)=="table" and type(dst)=="table" then
            for key,val in pairs(src.props) do

    function watch(var,name)
        name=name or "[var]"
        local p,i=vars[name],inspect(var)

    function clear()

    function draw(dx,dy,w,h)
        dx=dx or 0
        dy=dy or 48
        w=w or 128-dx
        h=h or 128-dy

        -- collapsed mode
        if not exp then

        -- window
        x=dx+2 y=dy+2-sy

        -- read mouse
        click=mb and not pb and mx>=dx and mx<dx+w and my>=dy and my<dy+h

        if exp then     

            -- variables                            
            for k,v in pairs(vars) do

            -- scrollbar
            local sh=y+sy-dy
            if sh>h then
                local sx=dx+w-4
                local by=sy/sh*h+dy
                local bh=h/sh*h
                rectfill(sx,by,dx+w,by+bh-1,sdrag and 12 or 6)
                if click and mx>=sx then
                    if my<by then
                    elseif my>by+bh then
                if sdrag then 
                if(not mb)sdrag=nil

            -- clear btn

        -- expand/collapse btn
        if(butn(exp and "-" or "+",dx+w-10,dy,14))exp=not exp

        -- draw mouse ptr

    function show()
        while exp do

    function prnt(v,name)

            return emp
            return exp

There are a few different ways to use it.

Global variables

You can view global variables when your program is paused by typing:


The window will popup and run until you click "-" at the top right to exit it.
Note: If you press "Esc" to exit the inspection window, and try to resume your game with "resume", it will resume the popup window instead! To avoid this, use the "-" button.

Local variables

To view a local variable inside a function you need to add code to that function to capture it.

dbg.watch(myvariable,"my variable")

This will capture it's value and add it to your variable list. The second parameter is the name. You can add multiple variables so long as they all have different names. Calling dbg.watch again with the same name causes it to replace the previous value.

To view your captured variables, pause your program by pressing Esc, and type:


Be aware that the variable inspector window shows the variable's value at the time dbg.watch() was executed. If the variable has been changed since, the changes will not show in the inspector. (This is deliberate.)

Displaying variables while the program is running

If you want to run the inspector window directly in your program, add:


to your _draw() function.

You can optionally specify the window position (x,y,width,height), e.g.


By default the window displays collapsed, until you click the "+" button.

Remember you still need to capture variables with "dbg.watch()", otherwise the window will be empty.

Pausing while the inspector is open

The game will continue running while the inspector window is open.
If you'd prefer it to pause the game, you can add:


to the top of your "_update" function.


returns true when the window is expanded or false when collapsed.
You can also force it open with:


or collapse it with:


For example, to invoke the editor from the Pico-8 built in menu:


Performance considerations

This snippet works by traversing your variables and building a "snapshot" tree structure. If you capture large variables every frame you might get some slow down, due to the traversal and possibly the Lua garbage collector cleaning up snapshots from previous frames. So make sure to remove your dbg.watch() calls when you want your program to run fast again.

P#76213 2020-05-09 02:37 ( Edited 2020-05-09 03:04)

Turn your 2D game into a 3D game!

That's 50% extra D!
100% guaranteed to work, sometimes, if you're lucky.
Simply paste this into the top of your 2D game, and be the envy of all your 2D coding friends!!!1!1

(OK, I'll stop now.)

This works best for top down games like "Pic-oh mummy!" by @Hokutoy, "Pakutto boy" by @Konimiru (both pictured)
Admittedly it's more of a gimmick/experiment - the result isn't very playable due to not being able to see the whole play area.

I mainly just wanted to see if it would work :)

  return (x-_.cx)-64,_.ch,128-(y-_.cy)
  local scale=_.d/z
  return x*scale+64,y*scale+_.ymid,scale

 _.cx=x or 0
 _.cy=(y or 0)+_.cyoff


 local wx,wy,wz=_.s2w(x,y)
 local px,py=_.proj(wx,wy,wz)

 local wx,wy,wz=_.s2w(x,y)
 local px,py,scale=_.proj(wx,wy,wz)

 w=w or sw
 h=h or sh
 local wx,wy,wz=_.s2w(x+w/2,y+h)
 local px,py,scale=_.proj(wx,wy,wz)
 local pw,ph=w*scale,h*scale

 -- sub pixel stuff
 local x0,x1=flr(px-pw/2),flr(px+pw/2)
 local y0,y1=flr(py-ph),flr(py)


 if(not n or not x or not y)return
 -- convert to equivalent sspr() call
 w=(w or 1)*8
 h=(h or 1)*8
 local sx,sy=flr(n%16)*8,flr(n/16)*8

 cx=cx or 0
 cy=cy or 0
 x=x or 0
 y=y or 0
 w=w or 128
 h=h or 64

 -- near/far corners
    local fx,fy,fz=_.s2w(x,y)
    local nx,ny,nz=_.s2w(x,y+h*8)

 -- clip

 -- project
 local npx,npy,nscale=_.proj(nx,ny,nz)
 local fpx,fpy,fscale=_.proj(fx,fy,fz)

 -- clamp

 -- rasterise
 local py=flr(npy)
 while py>=fpy do

  -- floor plane intercept
        local g=(py-_.ymid)/_.d
        local z=_.ch/g      

        -- map coords
        local mx,my=cx,(fz-z)/8+cy

        -- project to get left/right
        local lpx,lpy,lscale=_.proj(nx,ny,z)
        local rpx,rpy,rscale=_.proj(nx+w*8,ny,z)

        -- delta x
        local dx=w/(rpx-lpx)

        -- sub-pixel correction
        local l,r=flr(lpx+0.5)+1,flr(rpx+0.5)

  -- render


EDIT 1: adjusted near plane to avoid numeric overflow. Defaults for omitted map() parameters.
EDIT 2: also 3Dise sspr, pset and circ
EDIT 3: sub-pixel logic
EDIT 4: add map() layer parameter. fix gaps between adjacent sprites.

New version!

I've made a new version called Instant 3D plus! :-).
It should behave exactly like the original, but it's cleaned up quite a bit, and you can call the 3D functions directly to fix the bits that it doesn't get right automatically - or place things in exact 3D positions (like up in the air).

More details in the other post.

P#75793 2020-05-04 11:57 ( Edited 2020-05-17 01:05)

This is an older work-in-progress version! Play the completed released version here.

Cart #mot_ramps-14 | 2020-05-25 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This is a little scaled-sprite 3D graphics engine inspired by the old classic game Power Drift.
Still work in progress. Needs some basic game-play rules (laps, win/lose etc) and some difficulty balancing. But it's playable.


  • Fixed bug in saving tracks to external cart.
  • Added a little bit of steering assist to help line up the jumps.
  • Some other tweaks I forget :)

Update 2

  • 2 tracks
  • Track selector
  • Trees generate in the same place

Update 3

  • New track
  • (Slightly) better physics/collisions
  • Finish line and corner signs

Update 4

  • New larger test track
  • Performance optimisations. LOD system. More aggressive view volume culling
  • Tweaked the steering

Update 5

  • More performance tweaks

Update 6

  • More performance tweaks, thanks to @freds72
  • Updated physics to support driving upside down!
  • New track with loop-the-loop (to test driving upside down :)

Update 7

  • AI cars. WIP. No collisions yet. Difficulty will probably be scaled down a bit eventually.
  • Moved editor to separate cart.
  • I tried to draw a palm tree.

Update 8

  • Different AI car colours.
  • Fixed flip-Y logic when AI cars are upside down.

*Update 9

  • Basic car collisions
  • AI cars now steer around each other (and you)

Update 10

  • Cockpit graphics with animated front wheels.
  • Main menu
  • Race start sequence

Update 11

  • Fix wheel animation when frame rate <30
  • Fix NPC cars getting stuck on hills

Update 12

  • Lap and position displayed on screen
  • Race finishes after 5 laps
  • Note: Difficulty level logic is not hooked up yet!

Update 13

  • Hook up difficulty levels
  • First attempt at engine sounds
  • "Ramps" logo :)
P#72871 2020-02-07 12:34 ( Edited 2020-07-07 08:39)

Cart #mot_dodgeballs-1 | 2019-11-14 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

A little <560 chars game.
Press left/right to dodge between the white balls.

Vaguely inspired by "Beam rider", so there's actually 5 lanes to jump between. I ran out of chars before I could draw the lanes though :)

P#69892 2019-11-14 10:06 ( Edited 2019-11-14 10:14)

Cart #mot_imgui-2 | 2019-11-12 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

For some reason I felt like writing a little immediate-mode GUI library.

It has:

  • Labels
  • Buttons
  • Check boxes
  • Radio buttons
  • Sliders
  • Text boxes

You write into the text boxes on a little popup keyboard.

It works best with the mouse, but it can run in controller-only mode, where you move the pointer around with the direction arrows (it's pretty cumbersome though).

"Immediate mode" means you call the functions to draw the widgets in your drawing code, and it returns the user's input. It's generally easier to integrate into projects than a traditional widget UI would be, as you don't have to create and manage objects, you just draw the UI controls you need where and when you need them.

The first tab in the source is the library. The second is a little demo, that doubles as the documentation :)

UPDATE: Better looking buttons (thanks @freds72)

P#69801 2019-11-11 08:08 ( Edited 2019-11-12 07:15)

Cart #tudanawati-10 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This tutorial is part 3 of a series. View part 1 here.

And the end of part 2 we had roadside objects drawn using scaled sprites and sections of the map.

Everything so far has been flat, so in this tutorial we will add some hills and valleys.
This will require solving some overlap issues which we will solve using a clip rectangle "trick", which will in turn set us up nicely for implementing tunnels - so we'll do that too.

Defining the pitch

First we'll define the pitch of each corner with a field called "pi" (not to be mistaken for the Greek letter and mathematical constant).


This will define the gradient at the start of each corner. So a "pitch" of 1 means the ground rises 1 unit for every unit it advances forward - a 45 degree incline. Likewise -1 would be a 45 degree decline. And 0 is of course level.

For brevity we've made the pitch optional - it will default to 0 if not supplied.

To make the hills and valleys smooth the pitch will smoothly interpolate between values across each corner. We will calculate the delta to add to the pitch for each segment in the _init() method:

 -- calculate the change in pitch
 -- per segment for each corner.
 for i=1,#road do
  local corner=road[i]
  local pi=corner.pi or 0
  local nextpi=road[i%#road+1].pi or 0

The pitch delta is stored in field "dpi" (not to be confused with "dots per inch" - naming stuff is hard).


The pitch affects the vertical direction of the road as it is drawn. We actually already have a "yd" variable which is added to the y coordinate after each segment is drawn. It's just that until now the yd has always been 0, so the ground has always been flat. Now we can use it to create the hills and valleys.

First we calculate the initial value at the start of _draw()

 -- direction
 local camang=camz*road[camcnr].tu
 local xd=-camang
 local yd=road[camcnr].pi+road[camcnr].dpi*(camseg-1)
 local zd=1

This is the start value "pi" plus the delta "dpi" added for every segment the camera has traversed along the corner.

Then we add "dpi" to the "yd" after each segment is drawn, similar to how we've added the turn "tu" to "xd":

  -- turn and pitch

This is all we need to give the road a smooth rising and falling effect.

Cart #tudanawati-6 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

A note on camera movement

It's worth pointing out that the camera automatically follows the shape of the hills and valleys smoothly, without us having to write any specific code.

This works, because the camera position is skewed in the direction of the segment it is on. Back in tutorial one we implemented the skew function like this:

function skew(x,y,z,xd,yd)
 return x+z*xd,y+z*yd,z

In particular the "y+z*yd" ensures the camera moves up and down with the shape of the road.

Storing positions "unskewed" and skewing them at draw time has some advantages. Regardless of how the road turns or pitches:

  • The ground is always at y=0
  • The center of the road is always at x=0
  • The sides of the road are always at x=+/-3

This approach will also make implementing AI cars easier later on.


The hills and valleys introduce some obvious overlap issues - sprites visible through hills, far away ground being drawn in front instead of behind.

One approach to fixing this would be to change the road drawing order so that it is back-to-front as well.
This would be a perfectly valid approach (although it would require careful management to incorporate the sprites and road/ground at the same time).

However we're going to use a different approach. We're going to use clipping rectangles to prevent far away road/ground being drawn over near objects.

It will work like this:

  • We start with a clipping rectangle covering the whole screen. I.e. nothing is clipped.
  • As we draw forward, we move the bottom of the clipping rectangle up so that it does not include the road and ground we have just drawn.
  • The clipping rectangle prevents anything drawn further down the road from overlapping with what we've already drawn. Anything that would overlap will simply be clipped away.

The advantage of this method is that we can continue drawing the road as we walk forward along it. We don't have to change the algorithm too much.
It also reduces overdraw, which was important back-in-the-day on platforms that were fill-rate limited. Pico-8 drawing is fast enough that it doesn't really matter though.

To start with we define the initial clip region before the main drawing loop:

 -- current clip region
 local clp={0,0,128,128}

The "clp" array defines the left, top, right and bottom values in that order.

We reduce the clip region after drawing each segment, immediately after adding the background sprites (for reasons we'll see later):

  -- reduce clip region

The "min" function ensures that the bottom of the rectangle only ever moves up, which is important for drawing crests of hills correctly.

"setclip" is simply a helper function that sets the Pico-8 clip region for drawing:

function setclip(clp)

Putting this together we get:

Cart #tudanawati-7 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Clipping sprites

The hills are no longer see through, but now the background sprites are not being drawn correctly. The problem is the sprites are being drawn after the road, when the clipping rectangle has been reduced to cover just the sky. We could reset the clipping rectangle to cover the whole screen before drawing the sprites, which would improve things, but sprites would still be visible through the hills.

What we really need to do is draw each sprite using the clipping rectangle that was active when its segment was drawn, which we can do by storing a copy of the clip rectangle in the sprites array.

We'll add a "clp" parameter to addbgsprite:

function addbgsprite(sp,sumct,bg,side,px,py,scale,clp)


 -- add to sprite array

It's important that we create a new array and copy each of the "clp" fields individually, so that we get a snapshot of the "clp" array at that point. Referencing "clp" directly would not work, because "clp" changes as the road is drawn.

Now we update the calls in the main drawing loop to pass in the clipping rectangle:

 -- add background sprites
 addbgsprite(sp,sumct,road[cnr].bgr, 1,px,py,scale,clp)
 addbgsprite(sp,sumct,road[cnr].bgc, 0,px,py,scale,clp)

Finally we apply the clipping rectangle in drawbgsprite:

function drawbgsprite(s)

With this in place we should have hills and valleys drawn correctly, including the background sprites.

Cart #tudanawati-8 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA


For the last part of this tutorial we will implement basic tunnels. Tunnels give racing games a cool change of environment and they're just fun to drive through.

And with the clipping rectangle logic is in place they're reasonably straightforward to implement.

It's essentially an extension of the clipping logic used for the ground. But now we also reduce the top of the clipping rectangle as we draw the tunnel ceiling, and the left and right sides as we draw the tunnel walls.

We'll start by defining the tunnel in our road:




Tunnel corners are denoted by "tnl=true".

I've placed the tunnel section towards the start of the road so that it's quicker to get to for testing and debugging. (It can be moved later once everything is working correctly).

Tunnel front face

Next we'll draw the tunnel face.
We need to detect the first corner tunnel ("tnl" is set to true) where the previous corner was not a tunnel, which we can do by tracking the tunnel flag for the current corner, and the previous corner.

We set the initial value of the previous tunnel flag before the main drawing loop:

 -- previous tunnel flag
 local ptnl=road[cnr].tnl

Strictly speaking this should be set to the "tnl" property of the previous segment, but it doesn't actually make any noticeable difference for our purposes.

Inside the main loop we compare it with the current segment's tunnel flag, and draw the tunnel face at the start of the tunnel:

 -- draw tunnel face
 local tnl=road[cnr].tnl
 if tnl and not ptnl then

Note that the tunnel face will be drawn at the start of the current segment. This means we must use the previous cursor position (ppx, ppy, pscale), as cursor positions are for the end of their segment.

We also need to copy "tnl" to "ptnl" just before the loop ends, so that "ptnl" is set correctly for the next segment:

 -- track previous projected position

We will draw the tunnel face by drawing rectangles around the mouth of the tunnel.
We'll start by creating a helper function that takes the projected road position and calculates a rectangle describing the tunnel floor, ceiling and walls.

function gettunnelrect(px,py,scale)
 local w,h=6.4*scale,4*scale
 local x1=ceil(px-w/2)
 local y1=ceil(py-h)
 local x2=ceil(px+w/2)
 local y2=ceil(py)
 return x1,y1,x2,y2

The red rectangle is the "tunnel rectangle". I.e. the mouth of the tunnel.

We're allowing 6.4 units of width for the road, rather than 6, because the red and white shoulder things stick out another 0.2 units each way.
The tunnel will be 4 units high, which is low enough to make the tunnel feel claustrophobic but high enough to be above the camera.

Using this we can implement drawtunnelface:

function drawtunnelface(px,py,scale)

 -- tunnel mouth 
 local x1,y1,x2,y2=gettunnelrect(px,py,scale)

 -- tunnel wall top
 local wh=4.5*scale
 local wy=ceil(py-wh)

 -- draw faces

Essentially we're drawing a rectangle that extends from the top of the facing wall down to the top of the tunnel mouth. Then we draw two more rectangles either side of the mouth down to the ground.

The last thing we need to do is restrict the clipping rectangle to the tunnel mouth.
We'll create this function to adjust the clipping rectangle:

function cliptotunnel(px,py,scale,clp)
 local x1,y1,x2,y2=gettunnelrect(px,py,scale)

And update the tunnel face drawing code in the main drawing loop:

 -- draw tunnel face
 local tnl=road[cnr].tnl
 if tnl and not ptnl then

Now we should have a front facing tunnel wall:

Cart #tudanawati-9 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Tunnel interior

Next we need to draw the tunnel interior. This will consist of the ceiling, walls and road.

First we need to separate the road drawing code from the ground drawing code, so that we can just draw the road when inside the tunnel. We'll move the ground drawing code out into it's own function:

function drawground(y1,y2,sumct)

 -- draw ground
 local gndcol=3

And delete the "draw ground" lines from drawroad.

We'll update the drawing code in the main loop to draw the ground or tunnel interior as appropriate, then draw the road:

  -- draw ground/tunnel walls
  local sumct=getsumct(cnr,seg)
  if tnl then

  -- draw road

We draw the tunnel walls by comparing the tunnel rectangles at the start and end of the current segment.

We draw a ceiling rectangle to connect the top of each tunnel rectangle.
Then we draw wall rectangles on each side to connect the left and right sides.

We'll use an alternating colour for effect.

function drawtunnelwalls(px,py,scale,ppx,ppy,pscale,sumct)

 -- colour
 local wallcol=0

 -- draw walls
 local x1,y1,x2,y2=gettunnelrect(px,py,scale)
 local px1,py1,px2,py2=gettunnelrect(ppx,ppy,pscale)


The final step is to update the reduce-clip-region logic in the main drawing loop to handle tunnels.

  -- reduce clip region
  if tnl then

And this completes our tunnel:

Cart #tudanawati-10 | 2019-11-09 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Next steps

This is the end of part 3. In part 4 we'll add some cars to overtake.

P#69744 2019-11-09 23:30 ( Edited 2019-11-10 08:29)

Cart #tudanawati-5 | 2019-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This tutorial is part 2 of a series. View part 1 here

At the end of part one we had a basic road with corners.

Next we'll add some background objects along the sides of the road. Pseudo-3D racers commonly have objects like trees, houses and signs spaced along the side of the road to make things more interesting.

Adding trees

I've added a few sprites to play with. We'll start by adding this tree along each side, every 3 segments.

Drawing is straightforward.
We can use the projected position and scale of the road at each segment to calculate the position and size of the tree to draw. Then we can pass this to the scale sprite command (sspr), and draw our tree.

For example:

if (sumct%3)==0 then
 local tx,ty=px-4.5*scale,py
 local tw,th=1.5*scale,3*scale

Will draw a 3x1.5 unit tree 4.5 units to the left of the center of the road (which is far enough to move it off the road).


Because we draw the road front-to-back, we can't just draw the trees at the same time. They must be drawn in back-to-front order so that the near trees appear in front, and it looks correct.

So instead we must create an array of tree sprites:

local sp={}

And add the position of each tree to the array inside the drawing loop:

if (sumct%3)==0 then
 -- left tree
 local tx,ty=px-4.5*scale,py
 local tw,th=1.5*scale,3*scale

 -- right tree

After the road is drawn, we have an array of tree positions in front-to-back order.
We can then loop through it backwards to draw them in back-to-front order.

for i=#sp,1,-1 do
function drawbgsprite(s)

Putting it all together we get:

Cart #tudanawati-1 | 2019-11-02 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Different background types

Now that the basic logic is working, we can extend it to support different background types.
First we need to define the background types, with enough information to position them and draw them at the correct size:

 img={8,0,16,32},   -- sprite image
 pos={1.5,0},     -- position rel 2 side of road
 siz={1.5,3},     -- size
 spc=3            -- spacing
 flpr=true            -- flip when on right hand side

Now we can assign a background type to each corner. (bgl is for the left hand side, bgr is for the right).


We'll use this information to populate the "sp" array.
We need to store a little bit more than before, like the width and height and sprite image to draw.
To keep the main loop clean we can put it in a function:

function addbgsprite(sp,sumct,bg,side,px,py,scale)
 if(not bg)return

 -- find position
 if bg.pos then

 -- calculate size
 local w,h=bg.siz[1]*scale,bg.siz[2]*scale

 -- flip horizontally?
 local flp=side>0 and bg.flpr

 -- add to sprite array

Note that the "side" parameter is -1 for objects on the left hand side and 1 for objects on the right.

We must call it from the main drawing loop. Once for the left hand side and once for the right:

addbgsprite(sp,sumct,road[cnr].bgr, 1,px,py,scale)

And finally we need to change the drawbgsprite to handle the new format:

function drawbgsprite(s)

And now we have trees and signs:

Cart #tudanawati-2 | 2019-11-02 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Tweaking sprite scaling

Just a quick tweak to the sprite scaling before we continue. Feel free to skip this section if it doesn't interest you.

You might have noticed the trees sometimes float 1 pixel above the ground.

This is due to how sspr converts its parameters into integers before drawing. The projection and scaling calculations produce position and size values with a fractional component. The sspr command simply discards the fraction and rounds down to the nearest integer, for both the position and size parameters.

I prefer for it to render the pixels between the top and bottom values. For example if a sprite has a top of 1.9 and a bottom of 5.7, I want it to render on scan lines 2,3,4 and 5. This is how the road rendering has been implemented, and it ensures that the rendered segments fit together cleanly with no gaps or overlap.

sspr however will truncate 1.9 to 1 and the height (5.7-1.9=3.8) down to 3, then render it on scan lines 1,2,3,4. So it appears one pixel higher.

But we don't have to let sspr do the rounding. We can perform our own explicit rounding and tell sspr exactly which rows and columns we want our sprite stretched over.
In this case the ceil(1.9) gives me the scan line to start drawing (line 2) and ceil(5.7) gives the scan line to stop drawing (line 6). Subtracting the two gives the number of scan lines I want covered (4), which I can pass to sspr as the height.

And the logic is similar for horizontal columns.

Here's the updated drawbgsprite:

function drawbgsprite(s)
 local x1=ceil(s.x-s.w/2)
 local x2=ceil(s.x+s.w/2)
 local y1=ceil(s.y-s.h)
 local y2=ceil(s.y)

And here's the result:

Cart #tudanawati-3 | 2019-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Bigger background objects

Scaled sprites work really well for background objects, but they can only get so big before we start to run out of Pico8 sprite space. A lot of pseudo 3D racers have nice big roadside objects like buildings and bridges to make things varied and interesting.

Pico8 has the sprite "map" where you can layout sprites to make much larger objects. So if we can scale sections of the map to the screen this would solve our problem. But Pico8 does not have a built in "scale map" command like sspr does for sprites.

Fortunately though, we can roll our own.

The idea is to loop over the map tiles and use the "mget" function to get the sprite for each position in the map. Then we can calculate its position and size on screen and use sspr to draw it.

function smap(mx,my,mw,mh,dx,dy,dw,dh)
 -- tile size on screen
 local tw,th=dw/mw,dh/mh

 -- loop over map tiles
 for y=0,mh-1 do
  for x=0,mw-1 do

   -- lookup sprite
   local s=mget(mx+x,my+y)

   -- don't draw sprite 0
   if s~=0 then

    -- sprite row and column index
    -- use to get sprite image coords
    local sc,sr=s%16,flr(s/16)      -- 16 sprites per row
    local sx,sy=sc*8,sr*8         -- 8x8 pixels per sprite

    -- sprite position on screen
    local x1=ceil(dx+x*tw)
    local y1=ceil(dy+y*th)
    local x2=ceil(dx+x*tw+tw)
    local y2=ceil(dy+y*th+th)

    -- scale sprite

mx,my,mw,mh are the map coordinates in cells. dx,dy,dw,dh are the screen coordinates to draw.
We can test this function by typing (in immediate mode):


Which should draw a scaled house across the screen.

Armed with our new function, we can add some houses to our map. This takes a little bit of plumbing.

First we define a background type for it:

 mp={0,0,8,5},           -- map image (x,y,w,h in tiles)

And add some houses to the end of our road:


We need to copy the "mp" property when we write the entry into the "sp" sprite array, in the "addbgsprite" function:

 -- add to sprite array

The last step is to update "drawbgsprite" to call our smap function when it receives a sprite with an "mp" property:

function drawbgsprite(s)
 if s.mp then
  local x1=ceil(s.x-s.w/2)
  local x2=ceil(s.x+s.w/2)
  local y1=ceil(s.y-s.h)
  local y2=ceil(s.y)

Putting it all together gives:

Cart #tudanawati-4 | 2019-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

It should be kept in mind that scaling a map results in a lot of sspr calls. Our 8x5 tile house has 40 sprites to draw (well really 38, as it skips the blank top left and right tiles). A larger building could have 100,200 or more.
So it's worth keeping an eye on the CPU usage to make sure Pico-8 isn't going to max out, and maybe space larger objects out a bit more.
Having said that, we're still only at 17% CPU tops, so Pico-8 definitely has the ability to handle a decent amount of scenery.

Bridges and beams

To finish off let's add some metal beams for the player to drive underneath. This will be a centered background object, which means it's technically in the middle of the road. However because the beam object is wider than the road and is essentially bridge shaped, the camera will drive through/underneath it, instead of crashing into it.

We have most of what we need already. We'll define a background type:


And add it to our road, using "bgc" to indicate it's a centered background object.


In the main drawing loop, we'll add another call to "addbgsprite" for centered objects:

 -- add background sprites
 addbgsprite(sp,sumct,road[cnr].bgr, 1,px,py,scale)
 addbgsprite(sp,sumct,road[cnr].bgc, 0,px,py,scale)

By passing 0 as the "side" parameter we cancel out any horizontal positioning, so that it ends up in the middle of the road.

And that's all we need to do:

Cart #tudanawati-5 | 2019-11-05 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Next steps

And that's it for part 2. Part 3 is about creating hills and tunnels.

P#69550 2019-11-05 10:08 ( Edited 2019-11-09 23:32)

Cart #ywosahuru-3 | 2020-05-21 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Reposting this in carts, because it's as finished as it's ever going to be :-).

This is a little SDF ray marcher I've been playing with.
It renders two randomly placed spheres and a torus above a checker-board plane in different colours. Often one of them is reflective.

The code is ugly as heck, and the specular highlights are completely wrong, but it occasionally spits out something pretty imo.

Update: Changed to use sqrt() again, as it's much more accurate in v0.2.0

P#69517 2019-10-31 07:24 ( Edited 2020-05-21 09:26)

Cart #yijebofuse-0 | 2019-10-29 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

I felt like ray marching a signed distance field in PICO-8.
(Don't ask me why..).

P#69443 2019-10-29 10:12

Cart #tudanawati-0 | 2019-10-27 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Pseudo 3D racing games are fun. They have a cool retro arcade feel, with a good sense of speed, and can run on low end hardware. Plus they're pretty straightforward to implement - and satisfying.

There are lots of different ways to write a pseudo 3D racer, but I'm just going to show you how I do it.
This is the method I used for Loose Gravel, and can render corners, hills, tunnels and background sprites in an efficient manner. It doesn't need any 3D drawing hardware, just basic 2D rectangles, lines, scaled sprites and rectangular clip regions. Pico-8 can do all of these.

Defining the road

The road is made out of "corners" (for our purposes we will call straight bits "corners" as well). Corners need to curve in the direction the road turns, so we will simulate this by building them out of smaller straight "segments".

We can define the track as an array of these corners.


Each corner has a segment count "ct" and a value indicating how much the direction turns between each segment "tu".
So tu=0 creates a straight piece, tu=1 will turn to the right, -1 left etc.

For simplicity we'll ignore hills and valleys for now.

Drawing the road

We will draw the road by walking a 3D "cursor" along it and drawing the road at each point.
We'll define the cursor like this:

local x,y,z=0,1,1

We will start drawing the road slightly in front (z=1) and below (y=1) the camera position.
Note: I use x=right, y=down, z=into the screen as my coordinate system. I find this easiest to work with, having x and y in the same direction as on the screen and keeping z coordinates positive.

The direction of the road is another 3D vector:

local xd,yd,zd=0,0,1

So initially the road will point straight forward (zd=1).
The direction will be added to the cursor's 3D position to move from the current segment to the start of the next. To keep the maths simple we're using segments of length 1.

We also need to track which corner and segment we are drawing:

local cnr,seg=1,1

The main drawing loop will draw 30 segments of the road from the starting position, as follows:

  • Draw the road at the current position
  • Move to the next position in 3D space
  • Adjust the direction based on how the road turns
  • Advance to the next segment (and corner if applicable)

Putting this together, gives us something like this:

Cart #tadirutora-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Click "code" up above to view the code.

It's just a static boring line for now, but the basic logic is there. I was pretty vague about what "draw the road" means so we're just drawing a line to the x and z coordinates of the "cursor" for now.

We can see that the road goes straight for a bit then turns to the left as it moves down the screen.
We're "adjusting the direction" by adding the turn amount for the current corner to the X coordinate of our direction vector:


which means we're actually skewing the road rather than rotating it. This is part of the "pseudo" in our pseudo 3D - the difference is if we were using proper rotation the road would eventually turn around and start coming back towards us - if it turned far enough - whereas with skewing it just keeps stretching out more and more horizontally.
Although less realistic, skewing is much simpler to implement, and means that the road will always face away from the camera, which makes drawing things in the right order a lot simpler. And as long as the corners aren't too sharp it's an acceptable approximation.

Making it 3D

The key making this 3D is called perspective projection.
This converts a 3D coordinate into a 2D screen coordinate. I won't bore you with the mathematics - there are plenty of other places you can find this information if you really want to.
The important thing is the formula, which is:

  • px=x*64/z+64
  • py=y*64/z+64

This gives a 90 degree field of view (FOV). Replacing the 64 in 64/z with a smaller value would give a wider FOV, or a larger value would give a narrower FOV. We'll stick with 64 however. The +64 moves everything into the center of the screen.

64/z is also a useful value to keep, because it is the scale factor for anything drawn at that position, such as scaled sprites, or the road width. So the project function will return this too:

function project(x,y,z)
 local scale=64/z
 return x*scale+64,y*scale+64,scale

With this we can replace the line drawing code in the main loop:

-- project
local px,py,scale=project(x,y,z)

-- draw road
local width=3*scale

The projection allows us to draw a horizontal line 6 units wide, scaled appropriately for the 3D position.
This produces something a little more like looking down a road.

Cart #gukusoggu-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Adding movement

Right now the road is static, because it is always drawn from the same position.
To get the sensation of movement we need to simulate a camera moving down the road, and draw it from the camera's position.

So we'll declare the camera:


And change "cursor" in the _draw() function to start from the camera position:

local cnr,seg=camcnr,camseg

We can use the same logic to advance the camera to the next segment as we do for the "cursor" when drawing, by moving it out into a function:

function advance(cnr,seg)
 if seg>road[cnr].ct then
 return cnr,seg

This advances to the next segment in the corner, and if necessary the next corner in the road, looping around to the first corner if required.

Then we call it from the _draw() function:

-- advance along road

And use it to advance the camera in _update():

function _update()

Putting it together we get:

Cart #sodarizetu-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

Which sort-of looks like movement, but isn't totally convincing.
The camera is moving one full segment per rendered frame, which means the segment lines are rendered at the same distance each time.
We need to move less than a full segment per rendered frame, which means we need to track the camera position relative to the current segment:


Now we can advance the camera by less than a full segment length:

function _update()
 if camz>1 then

Inside _draw() we start drawing relative to the camera position, by subtracting the camera coordinates from the starting coordinates.

local x,y,z=-camx,-camy+1,-camz+1

With these changes the forward movement feels more convincing:

Cart #fumibitub-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

But now cornering feels janky.
This is because the camera is always aligned exactly with the segment it is on, so when it moves to the next segment it snaps sharply.

To counter this we need to turn the camera smoothly towards the next segment's angle as it progresses down the current segment. We can compute this angle in _draw() as:

local camang=camz*road[camcnr].tu

Then subtract it from the initial cursor direction:

local xd,yd,zd=-camang,0,1

This gives some improvement:

Cart #kojoduyono-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

It's still not 100% though - there's still some horizontal juddering.

This can be a little tricky to understand the cause of.

The gist of it is that by turning the camera, we're skewing the first segment will be rendered. But when we calculate the cursor position relative to the camera, we're using the un-skewed camera offset. So when we draw the road forward again, the part that should pass through the camera point will actually be skewed left or right of it. This makes the camera appear to diverge from the path of the road as it moves towards the end of the segment. It then snaps back into the center when it progresses to the next segment.

To fix this issue we need to first skew the camera position in the "cursor" direction, then calculate the cursor position relative to the skewed camera position.

We'll start by creating a basic skew function:

function skew(x,y,z,xd,yd)
 return x+z*xd,y+z*yd,z

Essentially we're skewing the Z axis from (0,0,1) to (xd,yd,1).

We'll need to re-order the "cursor" setup code in _draw(), so that the direction is calculated first.
I.e. move this bit in front of the initial x,y,z calculation:

-- direction
local camang=camz*road[camcnr].tu
local xd,yd,zd=-camang,0,1

Then we can calculate the skewed camera position:

local cx,cy,cz=skew(camx,camy,camz,xd,yd)

And calculate the initial "cursor" position relative to the skewed camera:

local x,y,z=-cx,-cy+1,-cz+1

This finally gives us nice smooth camera movement:

Cart #makiybusu-0 | 2019-10-26 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

This is the core road drawing algorithm for a pseudo 3D racer.

The last step is to simply clean up the rendering so it's not just white lines on black.
With a little bit of work we can turn it into something like this:

Cart #tudanawati-0 | 2019-10-27 | Code ▽ | Embed ▽ | License: CC4-BY-NC-SA

I won't go into too much detail here - you can refer to the cartridge code for specifics - I'll just touch on a few basic points.

To draw the road we need to render a trapezium (also known as a trapezoid). Essentially we're joining the horizontal lines together and filling them in. Pico-8 doesn't have a built in trapezium drawing function, but we can roll our own by stacking 1-pixel high rectangles.

We use alternating colours to communicate speed, which is a common technique in pseudo 3D racers. The easiest way to do this is to track how many segments we are along the road as a whole. Then we can use the modulo operator (%) to determine whether we are on an odd or even segment, or every 6th segment etc, and use that to select a colour.
We pre-calculate this (as "sumct") for each corner of the road in an _init() function. This makes it easy to calculate for any corner and segment:

function getsumct(cnr,seg)
 return road[cnr].sumct+seg-1

We use this to alternate the ground colour every 3 segments.

We don't have to stop at just drawing a plain gray road. The projected positions, trapezium drawing routine and colour alternation give us the tools we need to draw other road features. So we've drawn road markings as a thin trapezium every 4 segments in the middle of the road, and shoulder barrier things on the sides of the road, alternating red and white every other segment.

With the basic rendering in place this is a good time to tweak the parameters to get the right look and feel. The following adjustments were made:

  • Moved the road start point to (0,2,2) in front of the camera
  • Reduced the corner "tu" values, as the corners were too sharp
  • Increased the movement speed from 0.1 to 0.3

Next steps

This feels like a good place to leave the first tutorial.

In part 2 we'll cover drawing roadside objects (and overhead objects) using scaled sprites.

P#69343 2019-10-27 02:03 ( Edited 2019-11-09 06:14)

I just noticed the += shorthand doesn't work the way I expected with comma separated values.

For example:


Sets x to 11 as expected, but y and z are set to 20 and 30 respectively, rather than 22 and 33.

Should the last line be equivalent to:



Or is there some reason I'm missing?

P#69302 2019-10-26 06:02

View Older Posts
Follow Lexaloffle:        
Generated 2020-09-22 02:16 | 0.269s | 4194k | Q:401