skia/ext/bitmap_platform_device_cairo.h

   1 // Copyright 2013 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_CAIRO_H_
   6 #define SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_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 SkBitmapDevice, public PlatformDevice {
  60  public:
  61   // Create a BitmapPlatformDeviceLinux from an already constructed bitmap;
  62   // you should probably be using Create(). This may become private later if
  63   // we ever have to share state between some native drawing UI and Skia, like
  64   // the Windows and Mac versions of this class do.
  65   //
  66   // This object takes ownership of @cairo.
  67   BitmapPlatformDevice(const SkBitmap& other, cairo_t* cairo);
  68   ~BitmapPlatformDevice() override;
  69
  70   // Constructs a device with size |width| * |height| with contents initialized
  71   // to zero. |is_opaque| should be set if the caller knows the bitmap will be
  72   // completely opaque and allows some optimizations.
  73   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
  74
  75   // Performs the same construction as Create.
  76   // Other ports require a separate construction routine because Create does not
  77   // initialize the bitmap to 0.
  78   static BitmapPlatformDevice* CreateAndClear(int width, int height,
  79                                               bool is_opaque);
  80
  81   // This doesn't take ownership of |data|. If |data| is NULL, the contents
  82   // of the device are initialized to 0.
  83   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
  84                                       uint8_t* data);
  85
  86   // Overridden from SkBaseDevice:
  87   void setMatrixClip(const SkMatrix& transform,
  88                      const SkRegion& region,
  89                      const SkClipStack&) override;
  90
  91   // Overridden from PlatformDevice:
  92   cairo_t* BeginPlatformPaint() override;
  93
  94  protected:
  95   SkBaseDevice* onCreateDevice(const CreateInfo&, const SkPaint*) override;
  96
  97  private:
  98   static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
  99                                       cairo_surface_t* surface);
 100
 101   // Sets the transform and clip operations. This will not update the Cairo
 102   // context, but will mark the config as dirty. The next call of LoadConfig
 103   // will pick up these changes.
 104   void SetMatrixClip(const SkMatrix& transform, const SkRegion& region);
 105
 106   // Loads the current transform and clip into the context.
 107   void LoadConfig();
 108
 109   // Graphics context used to draw into the surface.
 110   cairo_t* cairo_;
 111
 112   // True when there is a transform or clip that has not been set to the
 113   // context.  The context is retrieved for every text operation, and the
 114   // transform and clip do not change as much. We can save time by not loading
 115   // the clip and transform for every one.
 116   bool config_dirty_;
 117
 118   // Translation assigned to the context: we need to keep track of this
 119   // separately so it can be updated even if the context isn't created yet.
 120   SkMatrix transform_;
 121
 122   // The current clipping
 123   SkRegion clip_region_;
 124
 125   DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
 126 };
 127
 128 }  // namespace skia
 129
 130 #endif  // SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_H_