// 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 "base/basictypes.h"
#include "base/compiler_specific.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 {
// -----------------------------------------------------------------------------
// 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);
virtual ~BitmapPlatformDevice();
// 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);
// Performs the same construction as Create.
// Other ports require a separate construction routine because Create does not
// initialize the bitmap to 0.
static BitmapPlatformDevice* CreateAndClear(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);
// Overridden from SkBaseDevice:
virtual void setMatrixClip(const SkMatrix& transform, const SkRegion& region,
const SkClipStack&) OVERRIDE;
// Overridden from PlatformDevice:
virtual cairo_t* BeginPlatformPaint() OVERRIDE;
virtual void DrawToNativeContext(PlatformSurface surface, int x, int y,
const PlatformRect* src_rect) OVERRIDE;
protected:
virtual SkBaseDevice* onCreateDevice(const SkImageInfo& info,
Usage usage) OVERRIDE;
private:
static BitmapPlatformDevice* Create(int width, int height, bool is_opaque,
cairo_surface_t* surface);
// Sets the transform and clip operations. This will not update the Cairo
// context, but will mark the config as dirty. The next call of LoadConfig
// will pick up these changes.
void SetMatrixClip(const SkMatrix& transform, const SkRegion& region);
// Loads the current transform and clip into the context.
void LoadConfig();
// 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_;
// Translation assigned to the context: we need to keep track of this
// separately so it can be updated even if the context isn't created yet.
SkMatrix transform_;
// The current clipping
SkRegion clip_region_;
DISALLOW_COPY_AND_ASSIGN(BitmapPlatformDevice);
};
} // namespace skia
#endif // SKIA_EXT_BITMAP_PLATFORM_DEVICE_CAIRO_H_