Dither.hx

package fx;

class Dither extends flixel.system.FlxAssets.FlxShader
{
	@:glFragmentSource('
		#pragma header
		
		const float scale = 2.0;
		
		float checker(vec2 coord)
		{
			return mod(floor(coord.x / scale) + floor(coord.y / scale), 2.0);
		}
		
		vec4 pixelColor(vec2 coord)
		{
			return texture2D(bitmap, coord / openfl_TextureSize);
		}
		
		vec4 bigPixelCenterColor(vec2 coord)
		{
			return pixelColor(coord + vec2(scale / 2.0, scale / 2.0));
		}
		
		vec2 bigPixelTopLeft(vec2 coord)
		{
			return vec2(coord.x - mod(coord.x, scale), coord.y - mod(coord.y, scale));
		}
		
		void main()
		{
			vec2 topLeft = bigPixelTopLeft(openfl_TextureCoordv * openfl_TextureSize);
			gl_FragColor = bigPixelCenterColor(topLeft);
			gl_FragColor.w = floor(gl_FragColor.w) * checker(topLeft);
		}
	')
	
	public function new() { super(); }
}
// meanwhile in my state
package;

import fx.Dither;

import flixel.FlxCamera;
import flixel.FlxG;
import flixel.FlxSprite;

import openfl.filters.ShaderFilter;

class MenuState extends flixel.FlxState
{
    override public function create()
    {
        FlxCamera.defaultCameras = [FlxG.camera];
        var shaderCam = new FlxCamera();
        shaderCam.setFilters([new ShaderFilter(new Dither())]);
        shaderCam.bgColor = 0;
        FlxG.cameras.add(shaderCam);

        var sprite = new MySprite();
        sprite.camera = shaderCam;
        add(sprite);
    }
}