Line data    Source code

       1             : #define R16_BITS     5
       2             : #define G16_BITS     6
       3             : #define B16_BITS     5
       4             : 
       5             : #define R16_SHIFT    (B16_BITS + G16_BITS)
       6             : #define G16_SHIFT    (B16_BITS)
       7             : #define B16_SHIFT    0
       8             : 
       9             : #define MASK 0xff
      10             : #define ONE_HALF 0x80
      11             : 
      12             : #define A_SHIFT 8 * 3
      13             : #define R_SHIFT 8 * 2
      14             : #define G_SHIFT 8
      15             : #define A_MASK 0xff000000
      16             : #define R_MASK 0xff0000
      17             : #define G_MASK 0xff00
      18             : 
      19             : #define RB_MASK 0xff00ff
      20             : #define AG_MASK 0xff00ff00
      21             : #define RB_ONE_HALF 0x800080
      22             : #define RB_MASK_PLUS_ONE 0x10000100
      23             : 
      24             : #define ALPHA_8(x) ((x) >> A_SHIFT)
      25             : #define RED_8(x) (((x) >> R_SHIFT) & MASK)
      26             : #define GREEN_8(x) (((x) >> G_SHIFT) & MASK)
      27             : #define BLUE_8(x) ((x) & MASK)
      28             : 
      29             : // This uses the same dithering technique that Skia does.
      30             : // It is essentially preturbing the lower bit based on the
      31             : // high bit
      32           0 : static inline uint16_t dither_32_to_16(uint32_t c)
      33             : {
      34           0 :     uint8_t b = BLUE_8(c);
      35           0 :     uint8_t g = GREEN_8(c);
      36           0 :     uint8_t r = RED_8(c);
      37           0 :     r = ((r << 1) - ((r >> (8 - R16_BITS) << (8 - R16_BITS)) | (r >> R16_BITS))) >> (8 - R16_BITS);
      38           0 :     g = ((g << 1) - ((g >> (8 - G16_BITS) << (8 - G16_BITS)) | (g >> G16_BITS))) >> (8 - G16_BITS);
      39           0 :     b = ((b << 1) - ((b >> (8 - B16_BITS) << (8 - B16_BITS)) | (b >> B16_BITS))) >> (8 - B16_BITS);
      40           0 :     return ((r << R16_SHIFT) | (g << G16_SHIFT) | (b << B16_SHIFT));
      41             : }
      42             : 
      43           0 : static inline uint16_t dither_8888_to_0565(uint32_t color, pixman_bool_t toggle)
      44             : {
      45             :     // alternate between a preturbed truncation and a regular truncation
      46           0 :     if (toggle) {
      47           0 :         return dither_32_to_16(color);
      48             :     } else {
      49           0 :         return convert_8888_to_0565(color);
      50             :     }
      51             : }