Method blend_sub_pin

core/src/processing/core/PImage.java:2466–2478

Subtract O = MAX(0, D - S)

(int dst, int src)

   * O = MAX(0, D - S)
   */
  private static int blend_sub_pin(int dst, int src) {
    int a = src >>> 24;

    int s_a = a + (a >= 0x7F ? 1 : 0);

    int rb = ((src & RB_MASK)    * s_a >>> 8);
    int gn = ((src & GREEN_MASK) * s_a >>> 8);

    return min((dst >>> 24) + a, 0xFF) << 24 |
        max((dst & RED_MASK)   - (rb & RED_MASK), 0) |
        max((dst & GREEN_MASK) - (gn & GREEN_MASK), 0) |
        max((dst & BLUE_MASK)  - (rb & BLUE_MASK), 0);
  }


  /**