source/blender/gpu/shaders/gpu_shader_2D_smooth_color_dithered_frag.glsl


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noperspective in vec4 finalColor;
out vec4 fragColor;

/* 4x4 bayer matrix prepared for 8bit UNORM precision error. */
#define P(x) (((x + 0.5) * (1.0 / 16.0) - 0.5) * (1.0 / 255.0))
const vec4 dither_mat4x4[4] = vec4[4](vec4(P(0.0), P(8.0), P(2.0), P(10.0)),
                                      vec4(P(12.0), P(4.0), P(14.0), P(6.0)),
                                      vec4(P(3.0), P(11.0), P(1.0), P(9.0)),
                                      vec4(P(15.0), P(7.0), P(13.0), P(5.0)));

void main()
{
  ivec2 tx1 = ivec2(gl_FragCoord.xy) % 4;
  ivec2 tx2 = ivec2(gl_FragCoord.xy) % 2;
  float dither_noise = dither_mat4x4[tx1.x][tx1.y];
  fragColor = finalColor + dither_noise;
}