rgb-mixing.lua

-- In RGB displays, each pixel contains 3 subpixels for red, green and blue.
-- The intensity of each subpixel can be changed independently.
-- Mixing different intensities of each allows for a large range of colors.

-- In this program, we'll use a similar approach.
-- Except our RGB subpixels can only be on or off, which limits us to 8 colors.

-- We can treat a PICO-8 color index like an RGB pixel by treating the first 3
-- bits as flags for each RGB subpixel.

-- Here's where we'll implement that model.
-- We're mapping each index to a color, based on how the RGB subpixels should mix.
for i=1,8 do
  pal(i,({
         -- 0 [000] black
    8,   -- 1 [001] red
    11,  -- 2 [010] green
    10,  -- 3 [011] green + red = yellow
    140, -- 4 [100] blue
    14,  -- 5 [101] blue + red = magenta
    12,  -- 6 [110] blue + green = cyan
    7    -- 7 [111] blue + green + red = white
  })[i],1)
end

-- Draw loop!
::_::
cls()

-- Print some text in the top left.
-- 8 appears black since we used i=1,8 in the pallete code above.
?"#pico8",0,0,8

-- Iterate the three layers: red, green, blue.
for i=0,2 do
  -- Z depth factor
  k=.25+i/60+cos(t()/8)/5

  -- Iterate over the pixels of the text.
  for y=0,5,.25 do
    for x=0,23,.25 do
      if pget(x,y)>0 then
        -- Destination pixel
        u=64+(x-11)/k
        v=64+(y-3)/k

        -- So how do we mix two color indexes? It should look like:
        --   red [001] + red   [001] = red    [001]
        --   red [001] + green [010] = yellow [011]
        -- This kind of operation is called bitwise OR.
        -- In PICO-8 it's provided by the bor() function.

        -- 2^i is the color of the current layer.
        -- We want to mix this color with the color currently at the
        -- destination pixel.
        pset(u,v,bor(2^i,pget(u,v)))
      end
    end
  end
end

flip()
goto _