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Hi,

I'm using a metatable for particles in my game. For example, when the player dies the sprite explodes in a burst of pixels. I use rnd() to off-set the player position with a random number, and as I generate a lot of different particles (based on the colors the character is composed of) I want to move the for-loop into the constructor.

Unfortunately, for some reason the randomness doesn't work when I build the for-loop inside the particle constructor. Compare these two examples:

For loop in caller function

particles={}
particle = {
    x_offset=0,
    y_offset=0,
}

function particle:new(o)

    self.__index = self

    local pi = setmetatable(o or {}, self)

    pi.x=pi.x-rnd(pi.x_offset)
    pi.y=pi.y-rnd(pi.y_offset)

    add(particles,pi)

end

function game_over()

    for i=1,6 do
        particle:new({x=p.x,y=p.y,x_offset=12,y_offset=8})
    end

end

Result: I end up with 6 particles, each with a different x and y value due to the rnd() function being passed the x_offset and y_offset values.

For loop in constructor

particles={}
particle = {
    x_offset=0,
    y_offset=0,
}

function particle:new(count,o)

    self.__index = self

    for i=1,count do
        local pi = setmetatable(o or {}, self)

        pi.x=pi.x-rnd(pi.x_offset)
        pi.y=pi.y-rnd(pi.y_offset)

        add(particles,pi)
    end
end

function game_over()

    particle:new(6,{x=p.x,y=p.y,x_offset=12,y_offset=8})

end

Result: I end up with 6 particles, but they all have the same x and y values. As if the rnd() is called only once and then applied to the other 5 iterations of the for-loop.

Questions

  1. Why does the code behave this way?
  2. What's the right pattern to apply here?
P#62086 2019-02-19 20:41

Introduction

I'm trying to implement my "map to table" conversion as proposed in my previous forum post. To this end I created two functions: one for iterating over the map and storing it in a multi-dimensional table (generate_world()) and one for iterating over that table and placing the sprites (build_world()).

Problem

I get it to nicely iterate through the map, print out the tiles it finds and (presumably) store it in a table. However, when iterating over the table things get awry. I do get it to iterate over the first dimension (when printing it returns [table]), but when iterating over the second dimension it's empty (doesn't print anything).

All help would be greatly appreciated!

Code

function generate_world()
    world={}

    t_x=0
    t_y=0
    max_x=48
    max_y=16

    print "generating world ..."
    for x=0,max_x do
        world[x]={}
        for y=0,max_y do
            sp=mget(x,y)
            if sp != 0 then
                print("tile: "..x..","..y..": "..sp)
                world[x][y] = sp
            end
        end
    end
    print "done"
end

function build_world()
    for x in all(world) do
        for y in all(x) do
            print(y)
            -- this actually never gets executed
        end
end
P#60896 2019-01-16 19:46

Hey all,

Introduction

I haven't done any development for many years and in general hardly did any game development. Now I'm getting back into it with the awesome Pico-8 and to get familiar with the engine and game dev I'm working on a platformer.

Current progress

The current status is that I have a player character, physics, a (very) basic map and some sound effects. It all works nicely and I'm currently working on items that the player can pick up (power-ups and such). Before moving forward I was hoping to learn some best practices from you all and get some feedback on my current approach.

Approach or implementing items

As I want to have rather large maps with many items I want to place items using the map editor, not by defining them manually in the code (as tweaking during play-testing would be a pita). At the same time I want the items to have some animation before they're picked up and of course an animation when they're picked up as well.

My current idea is to scan the map during _init() using mget() for these items and then add them to an array which would be scanned and updated during the game loop. The idea is to iterate over the elements in the array and use mset() to change the tiles to do the animation before they're picked up.

Then I'm using collision detection to detect whether the player is picking up an item and if so play a sound effect + run an animation.

Feedback please

  • Does the above approach make sense or is there a better way to achieve this?
  • What are the pros/cons? Are there any alternatives?
  • Wouldn't iterating over the entire map to move the items to an array be too slow?
  • Can I do the loading in chunks based on what's in view? (e.g. using the camera position)

All help is very much appreciated!

P#60881 2019-01-16 07:58

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