text: // Copyright 2013 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  #ifndef SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_H_
  #define SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_H_
  
  #include <stdint.h>
  
  #include "base/compiler_specific.h"
  #include "base/macros.h"
  #include "base/memory/ref_counted.h"
  #include "skia/ext/platform_device.h"
  
  typedef struct _cairo_surface cairo_surface_t;
  
  // -----------------------------------------------------------------------------
  // Image byte ordering on Linux:
  //
  // Pixels are packed into 32-bit words these days. Even for 24-bit images,
  // often 8-bits will be left unused for alignment reasons. Thus, when you see
  // ARGB as the byte order you have to wonder if that's in memory order or
  // little-endian order. Here I'll write A.R.G.B to specifiy the memory order.
  //
  // GdkPixbuf's provide a nice backing store and defaults to R.G.B.A order.
  // They'll do the needed byte swapping to match the X server when drawn.
  //
  // Skia can be controled in skia/include/corecg/SkUserConfig.h (see bits about
  // SK_R32_SHIFT). For Linux we define it to be ARGB in registers. For little
  // endian machines that means B.G.R.A in memory.
  //
  // The image loaders are controlled in
  // webkit/port/platform/image-decoders/ImageDecoder.h (see setRGBA). These are
  // also configured for ARGB in registers.
  //
  // Cairo's only 32-bit mode is ARGB in registers.
  //
  // X servers commonly have a 32-bit visual with xRGB in registers (since they
  // typically don't do alpha blending of drawables at the user level. Composite
  // extensions aside.)
  //
  // We don't use GdkPixbuf because its byte order differs from the rest. Most
  // importantly, it differs from Cairo which, being a system library, is
  // something that we can't easily change.
  // -----------------------------------------------------------------------------
  
  namespace skia {
  
  class ScopedPlatformPaint;
  
  // -----------------------------------------------------------------------------
  // This is the Linux bitmap backing for Skia. We create a Cairo image surface
  // to store the backing buffer. This buffer is BGRA in memory (on little-endian
  // machines).
  //
  // For now we are also using Cairo to paint to the Drawables so we provide an
  // accessor for getting the surface.
  //
  // This is all quite ok for test_shell. In the future we will want to use
  // shared memory between the renderer and the main process at least. In this
  // case we'll probably create the buffer from a precreated region of memory.
  // -----------------------------------------------------------------------------
  class BitmapPlatformDevice : public SkBitmapDevice, public PlatformDevice {
   public:
    // Create a BitmapPlatformDeviceLinux from an already constructed bitmap;
    // you should probably be using Create(). This may become private later if
    // we ever have to share state between some native drawing UI and Skia, like
    // the Windows and Mac versions of this class do.
    //
    // This object takes ownership of @cairo.
    BitmapPlatformDevice(const SkBitmap& other, cairo_t* cairo);
    ~BitmapPlatformDevice() override;
  
    // Constructs a device with size |width| * |height| with contents initialized
    // to zero. |is_opaque| should be set if the caller knows the bitmap will be
    // completely opaque and allows some optimizations.
    static BitmapPlatformDevice* Create(int width, int height, bool is_opaque);
  
    // This doesn't take ownership of |data|. If |data| is NULL, the contents
    // of the device are initialized to 0.
    static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                        uint8_t* data);
  
   protected:
    SkBaseDevice* onCreateDevice(const CreateInfo&, const SkPaint*) override;
  
   private:
    // Overridden from PlatformDevice:
    cairo_t* BeginPlatformPaint(const SkMatrix& transform,
                                const SkIRect& clip_bounds) override;
  
    static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
                                        cairo_surface_t* surface);
  
    // Loads the current transform and clip into the context.
    void LoadConfig(const SkMatrix& transform, const SkIRect& clip_bounds);
  
    // Graphics context used to draw into the surface.
    cairo_t* cairo_;
  
    // True when there is a transform or clip that has not been set to the
    // context.  The context is retrieved for every text operation, and the
    // transform and clip do not change as much. We can save time by not loading
    // the clip and transform for every one.
    bool config_dirty_;
  
    DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
    friend class ScopedPlatformPaint;
  };
  
  }  // namespace skia
  
  #endif  // SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_H_
  