extern number time;

extern mat4 palette;

vec4 effect(vec4 colour, Image texture, vec2 texture_coords, vec2 screen_coords)
{
	vec4 base = Texel(texture, texture_coords);
	number grey = (base.r + base.g + base.b)/3;

	vec4 swapped, next;
	if(grey < 0.25)
	{
		swapped = palette[int(mod(floor(time), 4))];
		next = palette[int(mod((floor(time) + 1), 4))];
	}
	else if(grey < 0.5)
	{
		swapped = palette[int(mod((floor(time) + 1), 4))];
		next = palette[int(mod((floor(time) + 2), 4))];
	}
	else if(grey < 0.75)
	{
		swapped = palette[int(mod((floor(time) + 2), 4))];
		next = palette[int(mod((floor(time) + 3), 4))];
	}
	else
	{
		swapped = palette[int(mod((floor(time) + 3), 4))];
		next = palette[int(mod((floor(time)), 4))];
	}
	swapped.a = next.a = 1;

 	return mix(swapped, next, time - floor(time));
}