glsl color blending algorithm

• multiply:

  result = base * blend;

• screen:

  result = vec4(1.0) - ((vec4(1.0) - blend) * (vec4(1.0) - base));

• darken:

  result = min ( blend , base ) ;

• lighten:

  result = max( blend, base );

• difference:

  result = abs( base - blend );

• negation:

  result = vec4(1.0) - abs( vec4(1.0) - base - blend );

• exclusion:

  result = base + blend - (2.0*base*blend);

• overlay:

  # per channel: if (base < 0.5) { result = 2.0 * base * blend; } else { result = vec4(1.0) - 2.0 * (vec4(1.0) - blend) * (vec4(1.0) - base); }

• hard light:

  # per channel: if (blend < 0.5) { result = 2.0 * base * blend; } else { result = vec4(1.0) - 2.0 * (vec4(1.0) - blend) * (vec4(1.0) - base); }

• soft light:

  # per channel: if (blend < 0.5) { result = 2.0 * base * blend + base*base - 2.0 * base*base*blend; } else { result = 2.0 * sqrt(base) * blend - sqrt(base) + 2.0 * base - 2.0 * base*blend; }

• dodge:

  result = base / (vec4(1.0) - blend);

• burn:

  result = vec4(1.0) - (vec4(1.0) - base) / blend;