zovirl [Lexaloffle Blog Feed]

Let's learn about tables!

Thu, 28 Sep 2023 04:00:10 UTC

If you feel like you don't understand Lua's tables, I hope this post helps. I use tables all the time when I'm programming; they are super useful. Let's study them so you can use them too!

Tables can do several different things, which makes them a bit tricky. We'll start by exploring a common use: using tables to store a list of things, such as:

A hand of cards: 2♠, 3♥, Q♦, K♣, J♣
A list of monsters: Ogre, goblin, slime mold
The positions of all the black checkers: 12, 24, 20, 27

Making lists

This makes an empty list:

items={}

This makes a list with the names of some things found in a forest:

items={'tree', 'rock', 'stream'}

Now items contains 3 things; you can think of it like 3 boxes:

The first box contains 'tree', the second contains 'rock', the third contains 'stream'.

Getting items out of a list

Each box has a number, called its "index". To get the value from the first box, we do items[1] like this:

> print(items[1])
tree

We can also store the index in a variable, like this:

> current_index=1
> print(items[current_index])
tree

To pick a random item from a list, we can use rnd():

> print(rnd(items))
stream
> print(rnd(items))
tree

Changing items in a list

We can change the value stored in a box by using its index. Here's how to replace 'rock' with 'moss':

> items[2]='moss'

Length of a list

To get the number of items in a list, we use #items:

> length=#items
> print(length)
3

Here's a common way to get the last item of the list. It uses the list's length as an index:

> print(items[#items])
stream

Adding items

Items can be added to a list using add().

This adds to the end of the list:

add(items, 'mushroom') -- adds at end

This adds at the start of the list:

add(items, 'wolf', 1) -- adds at index 1

Deleting items

We can delete items by value:

del(items, 'tree')

or by index:

deli(items,2)

Looping over a list

We can access every item in a list using a for loop and all():

for item in all(items) do
 print(item)
end

That would print this:

wolf
stream
mushroom

If you need the index too, you can use a numeric for loop from 1 up to the length of the list:

for i=1,#items do
  print(i..': '..items[i])
end

That would print this:

1: wolf
2: stream
3: mushroom

Ok, that's it for lists.

Wow, that turned out longer than I expected. I also want to explore using tables to store dictionaries, but before I do, does anyone have any questions? Or feedback? Is this useful? Would it be better with more (or less) detail? Let me know what you think...

Would a "math for games" tutorial be useful? Or a collisions tutorial?

Sat, 19 Aug 2023 00:07:32 UTC

I feel like making a set of tutorial carts. What topic would help people the most?

I was thinking of a simple introduction to math for games, since that topic comes up frequently on the forums. Or maybe how to do collision detection? I see people asking about that fairly often too.

Any thoughts? Or suggestions of a topic? Would you find this useful?

Minotaur

Fri, 07 Apr 2023 03:42:59 UTC

minotaur_v1

by zovirl

[Click to Play]

King Minos has thrown you into the minotaur's labrynth! Can you kill the minotaur, rescue your fellow Athenians, and find your way out of the labrynth?

Controls:
Arrows to move.
Z to attack.

Perspective-correct texture mapping

Fri, 06 Nov 2020 05:29:03 UTC

3D texture mapping with tline (plus some other stuff, like wireframe rendering, and solid color polygon rendering). Did this as a learning project, to study old-school pre-GPU 3D graphics.

Thanks to freds72 and johanp for inspiration & example code.

texture_map_0

by zovirl

[Click to Play]

References if you want to learn.
http://www.multi.fi/~mbc/sources/fatmap2.txt
https://chrishecker.com/miscellaneous_technical_articles#perspective_texture_mapping
https://www.cs.cmu.edu/~fp/courses/graphics/pdf-color/14-raster.pdf
https://en.wikipedia.org/wiki/digital_differential_analyzer_(graphics_algorithm)
https://en.wikipedia.org/wiki/selection_sort
https://en.wikipedia.org/wiki/sutherland%e2%80%93hodgman_algorithm
Book: "Computer Graphics: Principles and Practice 2nd ed."

Anonymous inline functions don't work in tabs?

Thu, 05 Nov 2020 05:27:36 UTC

bug_anon_inline_func

by zovirl

[Click to Play]

I'm trying to use anonymous inline functions and I'm finding some weird behavior when they are on tabs.

Putting everything in tab #0 works:

x=1
function _draw()
 cls(1)
 print('x is '..x)
end

(function()
 x=2
end)()

And moving the inline function call to tab #1 works:

x=1
function _draw()
 cls(1)
 print('x is '..x)
end

-->8
(function()
 x=3
end)()

But putting an inline function call on both tab #0 and tab #1 does not work:

x=1
function _draw()
 cls(1)
 print('x is '..x)
end

(function()
 x=2
end)()

-->8
(function()
 x=3
end)()

I don't understand why. It gives this error:

runtime error line 7 tab 0
(function()
attempt to call a nil value
at line 7 (tab 0)

Why is this cart so slow on Raspberry Pi Zero?

Mon, 29 Jun 2020 00:59:33 UTC

I'm trying to figure out why this cart only runs at 10 FPS on a Raspberry Pi Zero. stat(1) returns 0.49 and stat(7) returns 30. However, the screen is only updating at 10-11 FPS. Other carts with higher stat(1) values don't show this problem, so it seems specific to something in this cart.

I can optimize to get the CPU usage down to 17%, and then the real framerate becomes acceptable. However, I'd actually like to understand why it is slow so I can work around it. (Also, I'd prefer to be able to use the whole CPU budget instead of just 17% of it!)

I assume what's happening is that the pico-8 CPU costs are optimistic for some instructions, and the actual cost on the Pi Zero hardware is higher. But which instructions?

Are there specific instructions I should be avoiding?

Are there specific types of drawing (like large map areas, or off-screen drawing) I should avoid?

Can I hook up a profiler to see what it is spending its time on?

The original raspberry pi post (https://www.lexaloffle.com/bbs/?tid=3085) says math-heavy carts run slowly. Is that still true?

Are there any performance tricks for writing carts that run well on a raspberry pi?

slow

by zovirl

[Click to Play]