An attempt of porting a triangle rasterizer (http://forum.devmaster.net/t/advanced-rasterization/6145) to pico-8

trifill.hx

static function trifill(x1:Fixed, y1:Fixed, x2:Fixed, y2:Fixed, x3:Fixed, y3:Fixed) {
	var dx12 = x1 - x2;
	var dx23 = x2 - x3;
	var dx31 = x3 - x1;
	//
	var dy12 = y1 - y2;
	var dy23 = y2 - y3;
	var dy31 = y3 - y1;
	//
	var minx = min(x1, min(x2, x3));
	var maxx = max(x1, max(x2, x3));
	var miny = min(y1, min(y2, y3));
	var maxy = max(y1, max(y2, y3));
	//
	var c1 = dy12 * x1 - dx12 * y1;
	var c2 = dy23 * x2 - dx23 * y2;
	var c3 = dy31 * x3 - dx31 * y3;
	//
	if (dy12 < 0 || (dy12 == 0 && dx12 > 0)) c1 += 1;
	if (dy23 < 0 || (dy23 == 0 && dx23 > 0)) c2 += 1;
	if (dy31 < 0 || (dy31 == 0 && dx31 > 0)) c3 += 1;
	//
	var cy1 = c1 + dx12 * miny - dy12 * minx;
	var cy2 = c2 + dx23 * miny - dy23 * minx;
	var cy3 = c3 + dx31 * miny - dy31 * minx;
	//
	for (y in flr(miny) ... flr(maxy)) {
		var cx1 = cy1;
		var cx2 = cy2;
		var cx3 = cy3;
		for (x in flr(minx) ... flr(maxx)) {
			if (cx1 > 0 && cx2 > 0 && cx3 > 0) {
				pset(x, y);
			}
			cx1 -= dy12;
			cx2 -= dy23;
			cx3 -= dy31;
		}
		cy1 += dx12;
		cy2 += dx23;
		cy3 += dx31;
	}
}

trifill.lua

function trifill(x1, y1, x2, y2, x3, y3)
	local dx12 = x1 - x2
	local dx23 = x2 - x3
	local dx31 = x3 - x1
	local dy12 = y1 - y2
	local dy23 = y2 - y3
	local dy31 = y3 - y1
	local minx = min(x1, min(x2, x3))
	local maxx = max(x1, max(x2, x3))
	local miny = min(y1, min(y2, y3))
	local maxy = max(y1, max(y2, y3))
	local c1 = dy12 * x1 - dx12 * y1
	local c2 = dy23 * x2 - dx23 * y2
	local c3 = dy31 * x3 - dx31 * y3
	if dy12 < 0 or dy12 == 0 and dx12 > 0 then
		c1 += 1
	end
	if dy23 < 0 or dy23 == 0 and dx23 > 0 then
		c2 += 1
	end
	if dy31 < 0 or dy31 == 0 and dx31 > 0 then
		c3 += 1
	end
	local cy1 = c1 + dx12 * miny - dy12 * minx
	local cy2 = c2 + dx23 * miny - dy23 * minx
	local cy3 = c3 + dx31 * miny - dy31 * minx
	for y = flr(miny), flr(maxy) - 1 do
		local cx1 = cy1
		local cx2 = cy2
		local cx3 = cy3
		for x = flr(minx), flr(maxx) - 1 do
			if cx1 > 0 and cx2 > 0 and cx3 > 0 then
				pset(x, y)
			end
			cx1 -= dy12
			cx2 -= dy23
			cx3 -= dy31
		end
		cy1 += dx12
		cy2 += dx23
		cy3 += dx31
	end
end