// VERTEX_SHADER:
// mask.glsl

void main() {
  gl_Position = u_projection * u_modelview * vec4(aPosition, 0.0, 1.0);

  vUv = vec2(aUv.x, aUv.y);
}

// FRAGMENT_SHADER:
// mask.glsl

uniform int u_mode;
uniform sampler2D u_mask;

float
luminance (vec3 color)
{
  return dot (vec3 (0.2126, 0.7152, 0.0722), color);
}

void main() {
  vec4 source = GskTexture(u_source, vUv);
  vec4 mask = GskTexture(u_mask, vUv);
  float mask_value;

  if (u_mode == 0)
    mask_value = mask.a;
  else if (u_mode == 1)
    mask_value = 1.0 - mask.a;
  else if (u_mode == 2)
    mask_value = luminance (mask.rgb);
  else if (u_mode == 3)
    mask_value = mask.a - luminance (mask.rgb);
  else
    mask_value = 0.0;

  gskSetOutputColor(vec4 (source * mask_value));
}