skia/ext/bitmap_platform_device_linux.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef SKIA_EXT_BITMAP_PLATFORM_DEVICE_LINUX_H_
   6 #define SKIA_EXT_BITMAP_PLATFORM_DEVICE_LINUX_H_
   7
   8 #include "base/basictypes.h"
   9 #include "base/compiler_specific.h"
  10 #include "base/memory/ref_counted.h"
  11 #include "skia/ext/platform_device.h"
  12
  13 typedef struct _cairo_surface cairo_surface_t;
  14
  15 // -----------------------------------------------------------------------------
  16 // Image byte ordering on Linux:
  17 //
  18 // Pixels are packed into 32-bit words these days. Even for 24-bit images,
  19 // often 8-bits will be left unused for alignment reasons. Thus, when you see
  20 // ARGB as the byte order you have to wonder if that's in memory order or
  21 // little-endian order. Here I'll write A.R.G.B to specifiy the memory order.
  22 //
  23 // GdkPixbuf's provide a nice backing store and defaults to R.G.B.A order.
  24 // They'll do the needed byte swapping to match the X server when drawn.
  25 //
  26 // Skia can be controled in skia/include/corecg/SkUserConfig.h (see bits about
  27 // SK_R32_SHIFT). For Linux we define it to be ARGB in registers. For little
  28 // endian machines that means B.G.R.A in memory.
  29 //
  30 // The image loaders are controlled in
  31 // webkit/port/platform/image-decoders/ImageDecoder.h (see setRGBA). These are
  32 // also configured for ARGB in registers.
  33 //
  34 // Cairo's only 32-bit mode is ARGB in registers.
  35 //
  36 // X servers commonly have a 32-bit visual with xRGB in registers (since they
  37 // typically don't do alpha blending of drawables at the user level. Composite
  38 // extensions aside.)
  39 //
  40 // We don't use GdkPixbuf because its byte order differs from the rest. Most
  41 // importantly, it differs from Cairo which, being a system library, is
  42 // something that we can't easily change.
  43 // -----------------------------------------------------------------------------
  44
  45 namespace skia {
  46
  47 // -----------------------------------------------------------------------------
  48 // This is the Linux bitmap backing for Skia. We create a Cairo image surface
  49 // to store the backing buffer. This buffer is BGRA in memory (on little-endian
  50 // machines).
  51 //
  52 // For now we are also using Cairo to paint to the Drawables so we provide an
  53 // accessor for getting the surface.
  54 //
  55 // This is all quite ok for test_shell. In the future we will want to use
  56 // shared memory between the renderer and the main process at least. In this
  57 // case we'll probably create the buffer from a precreated region of memory.
  58 // -----------------------------------------------------------------------------
  59 class BitmapPlatformDevice : public SkDevice, public PlatformDevice {
  60   // A reference counted cairo surface
  61   class BitmapPlatformDeviceData;
  62
  63  public:
  64   // Create a BitmapPlatformDeviceLinux from an already constructed bitmap;
  65   // you should probably be using Create(). This may become private later if
  66   // we ever have to share state between some native drawing UI and Skia, like
  67   // the Windows and Mac versions of this class do.
  68   //
  69   // This object takes ownership of @data.
  70   BitmapPlatformDevice(const SkBitmap& other, BitmapPlatformDeviceData* data);
  71   virtual ~BitmapPlatformDevice();
  72
  73   // Constructs a device with size |width| * |height| with contents initialized
  74   // to zero. |is_opaque| should be set if the caller knows the bitmap will be
  75   // completely opaque and allows some optimizations.
  76   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
  77
  78   // Performs the same construction as Create.
  79   // Other ports require a separate construction routine because Create does not
  80   // initialize the bitmap to 0.
  81   static BitmapPlatformDevice* CreateAndClear(int width, int height,
  82                                               bool is_opaque);
  83
  84   // This doesn't take ownership of |data|. If |data| is NULL, the contents
  85   // of the device are initialized to 0.
  86   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
  87                                       uint8_t* data);
  88
  89   // Overridden from SkDevice:
  90   virtual void setMatrixClip(const SkMatrix& transform, const SkRegion& region,
  91                              const SkClipStack&) OVERRIDE;
  92
  93   // Overridden from PlatformDevice:
  94   virtual cairo_t* BeginPlatformPaint() OVERRIDE;
  95   virtual void DrawToNativeContext(PlatformSurface surface, int x, int y,
  96                                    const PlatformRect* src_rect) OVERRIDE;
  97
  98  protected:
  99   virtual SkDevice* onCreateCompatibleDevice(SkBitmap::Config, int width,
 100                                              int height, bool isOpaque,
 101                                              Usage usage) OVERRIDE;
 102
 103  private:
 104   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
 105                                       cairo_surface_t* surface);
 106
 107   scoped_refptr<BitmapPlatformDeviceData> data_;
 108
 109   DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
 110 };
 111
 112 }  // namespace skia
 113
 114 #endif  // SKIA_EXT_BITMAP_PLATFORM_DEVICE_LINUX_H_