gfx/thebes/gfxColor.h

   1 /* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef GFX_COLOR_H
   7 #define GFX_COLOR_H
   8
   9 #include "mozilla/Attributes.h"  // for MOZ_ALWAYS_INLINE
  10 #include "mozilla/gfx/Types.h"   // for mozilla::gfx::SurfaceFormatBit
  11
  12 /**
  13  * Fast approximate division by 255. It has the property that
  14  * for all 0 <= n <= 255*255, GFX_DIVIDE_BY_255(n) == n/255.
  15  * But it only uses two adds and two shifts instead of an
  16  * integer division (which is expensive on many processors).
  17  *
  18  * equivalent to ((v)/255)
  19  */
  20 #define GFX_DIVIDE_BY_255(v) \
  21   (((((unsigned)(v)) << 8) + ((unsigned)(v)) + 255) >> 16)
  22
  23 /**
  24  * Fast premultiply
  25  *
  26  * equivalent to (((c)*(a))/255)
  27  */
  28 uint8_t MOZ_ALWAYS_INLINE gfxPreMultiply(uint8_t c, uint8_t a) {
  29   return GFX_DIVIDE_BY_255((c) * (a));
  30 }
  31
  32 /**
  33  * Pack the 4 8-bit channels (A,R,G,B)
  34  * into a 32-bit packed NON-premultiplied pixel.
  35  */
  36 uint32_t MOZ_ALWAYS_INLINE gfxPackedPixelNoPreMultiply(uint8_t a, uint8_t r,
  37                                                        uint8_t g, uint8_t b) {
  38   return (((a) << mozilla::gfx::SurfaceFormatBit::OS_A) |
  39           ((r) << mozilla::gfx::SurfaceFormatBit::OS_R) |
  40           ((g) << mozilla::gfx::SurfaceFormatBit::OS_G) |
  41           ((b) << mozilla::gfx::SurfaceFormatBit::OS_B));
  42 }
  43
  44 /**
  45  * Pack the 4 8-bit channels (A,R,G,B)
  46  * into a 32-bit packed premultiplied pixel.
  47  */
  48 uint32_t MOZ_ALWAYS_INLINE gfxPackedPixel(uint8_t a, uint8_t r, uint8_t g,
  49                                           uint8_t b) {
  50   if (a == 0x00)
  51     return 0x00000000;
  52   else if (a == 0xFF) {
  53     return gfxPackedPixelNoPreMultiply(a, r, g, b);
  54   } else {
  55     return ((a) << mozilla::gfx::SurfaceFormatBit::OS_A) |
  56            (gfxPreMultiply(r, a) << mozilla::gfx::SurfaceFormatBit::OS_R) |
  57            (gfxPreMultiply(g, a) << mozilla::gfx::SurfaceFormatBit::OS_G) |
  58            (gfxPreMultiply(b, a) << mozilla::gfx::SurfaceFormatBit::OS_B);
  59   }
  60 }
  61
  62 #endif /* _GFX_COLOR_H */