Bayer dithering in TIC-80

bayer.lua

local bayerMatrix = {
    0, 8, 2, 10,
    12, 4, 14, 6,
    3, 11, 1, 9,
    15, 7, 13, 5
}

function ditherPixel(x, y, col1, col2, level)
    local threshold = bayerMatrix[x % 4 + y % 4 * 4 +1] -- Remove the +1 for 0-based arrays
    return (level < threshold) and col1 % 15 or col2 % 15
end

local color1 = 0
local color2 = 1
local level = 0

function TIC()
    cls(0)
    level = level + 0.25
    if level % 15 == 0 then
        color1 = color2
        color2 = color2 + 1
    end
    
    for x=0,15 do
        for y=0,15 do
            local px = ditherPixel(x, y, color1, color2, level % 15)
            pix(x,y,px)
        end
    end

    for x=31,60 do
        for y=0,135 do
            local px = ditherPixel(x, y, color1, color2, y / (136 / 15))
            pix(x,y,px)
        end
    end
end