circles.lua

require "gd"

size = 400
cenx = 125
ceny = 275

im = gd.createPalette(size, size)
assert(im)

black = im:colorAllocate(0, 0, 0)
im:gifAnimBegin("out.gif", true, 0)

r = 100
astep = math.pi
for i = 1, 15 do
    local tim = gd.createTrueColor(size, size)
    --tim:setAntiAliased(tim:colorAllocate(0, 0, 0))
    for c = 14, 0, -1 do
        local ccenx = cenx+16*c+i
        local cceny = ceny-16*c-i
        local angles = {}
        for angle = 0, 2*math.pi, astep*math.pow(0.98, 15*c) do
            table.insert(angles, angle)
        end
        local points = {}
        for a = 1, #angles do
            table.insert(points, {
                ccenx+r*math.cos(angles[a]),
                cceny+r*math.sin(angles[a])})
        end
        local w = (380-ccenx)%256
        tim:filledPolygon(points, tim:colorAllocate(w, w, w))
        tim:polygon(points, tim:colorAllocate(0, 0, 0))
        --[[
        for p = 1, #points-1 do
            tim:line(points[p][1], points[p][2], points[p+1][1], points[p+1][2], gd.ANTI_ALIASED)
        end
        tim:line(points[#points][1], points[#points][2], points[1][1], points[1][2], gd.ANTI_ALIASED)
        --]]
    end
    astep = astep*0.98
    local ti = tim:createPaletteFromTrueColor(true, 8)
    ti:gifAnimAdd("out.gif", true, 0, 0, 5, gd.DISPOSAL_NONE)
    io.write(i.." ")
end

gd.gifAnimEnd("out.gif")