WhyCan Forum(哇酷开发者社区)

/* Dither Tresshold for Red Channel */
static const BYTE dither_tresshold_r[64] = {
  1, 7, 3, 5, 0, 8, 2, 6,
  7, 1, 5, 3, 8, 0, 6, 2,
  3, 5, 0, 8, 2, 6, 1, 7,
  5, 3, 8, 0, 6, 2, 7, 1,

  0, 8, 2, 6, 1, 7, 3, 5,
  8, 0, 6, 2, 7, 1, 5, 3,
  2, 6, 1, 7, 3, 5, 0, 8,
  6, 2, 7, 1, 5, 3, 8, 0
};

/* Dither Tresshold for Green Channel */
static const BYTE dither_tresshold_g[64] = {
  1, 3, 2, 2, 3, 1, 2, 2,
  2, 2, 0, 4, 2, 2, 4, 0,
  3, 1, 2, 2, 1, 3, 2, 2,
  2, 2, 4, 0, 2, 2, 0, 4,

  1, 3, 2, 2, 3, 1, 2, 2,
  2, 2, 0, 4, 2, 2, 4, 0,
  3, 1, 2, 2, 1, 3, 2, 2,
  2, 2, 4, 0, 2, 2, 0, 4
};

/* Dither Tresshold for Blue Channel */
static const BYTE dither_tresshold_b[64] = {
  5, 3, 8, 0, 6, 2, 7, 1,
  3, 5, 0, 8, 2, 6, 1, 7,
  8, 0, 6, 2, 7, 1, 5, 3,
  0, 8, 2, 6, 1, 7, 3, 5,

  6, 2, 7, 1, 5, 3, 8, 0,
  2, 6, 1, 7, 3, 5, 0, 8,
  7, 1, 5, 3, 8, 0, 6, 2,
  1, 7, 3, 5, 0, 8, 2, 6
};

/* Get 16bit closest color */
BYTE closest_rb(BYTE c) { 
  return (c >> 3 << 3); /* red & blue */
}
BYTE closest_g(BYTE c) {
  return (c >> 2 << 2); /* green */
}

/* RGB565 */
WORD RGB16BIT(BYTE r, BYTE g, BYTE b) {
  return ((WORD)((r>>3)<<11)|((g>>2)<<5)|(b>>3));
}

/* Dithering by individual subpixel */
WORD dither_xy(
  int x, 
  int y, 
  BYTE r, 
  BYTE g, 
  BYTE b
){
  /* Get Tresshold Index */
  BYTE tresshold_id = ((y & 7) << 3) + (x & 7);

  r = closest_rb(
          MIN(r + dither_tresshold_r[tresshold_id], 0xff)
       );
  g = closest_g(
          MIN(g + dither_tresshold_g[tresshold_id], 0xff)
       );
  b = closest_rb(
          MIN(b + dither_tresshold_b[tresshold_id], 0xff)
       );
  return RGB16BIT(r, g, b);
}

/* Dithering Pixel from 32/24bit RGB 
*
* GetR, GetG, GetB -> Function to get individual color in pixel
*
*/
WORD dither_color_xy(int x, int y, DWORD col) {
  return dither_xy(x, y, GetR(col), GetG(col), GetB(col));
}

/* EXAMPLES */
void ExampleDither1(WORD * dest, DWORD * src, int width, int height){
  int x, y;
  for (y=0; y<height; y++){
    for (x=0; x<width; x++){
      int pos = y * width + x;
      dest[pos] = dither_color_xy(x,y,src[pos]);
    }
  }
}
void ExampleDither2(WORD * dest, BYTE * src, int width, int height){
  int x, y;
  for (y=0; y<height; y++){
    for (x=0; x<width; x++){
      int pos = y * width + x;
      dest[pos] = dither_xy(x,y,src[pos*3],src[pos*3+1],src[pos*3+2]);
    }
  }
}