WIP RasterCanvasLayerAllocator experiment 2

include/core/SkRasterCanvasLayerAllocator.h

Index: include/core/SkRasterCanvasLayerAllocator.h
diff --git a/include/core/SkRasterCanvasLayerAllocator.h b/include/core/SkRasterCanvasLayerAllocator.h
new file mode 100644
index 0000000000000000000000000000000000000000..7c9a868d358474d2d488a7c09859da04c30a87bd
--- /dev/null
+++ b/include/core/SkRasterCanvasLayerAllocator.h
@@ -0,0 +1,91 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkRasterCanvasLayerAllocator_DEFINED
+#define SkRasterCanvasLayerAllocator_DEFINED
+
+#include "SkImageInfo.h"
+#include "SkRefCnt.h"
+#include "SkSurfaceProps.h"
+
+class SkBaseDevice;
+class SkCanvas;
+
+/**
+ * Base class to encapsulate platform-specific bitmap allocations.
+ *
+ * Bitmaps may outlive this allocator object, so callbacks must be
+ * used to make sure they get torn down as required by the platform;
+ * see SkManagedBitmapDevice for a minimal implementation.
+ *
+ * Implementations must track the pairings between the buffer allocated
+ * and the matching native context.
+ *
+ * For example, on Windows one might create an HBITMAP (using
+ * CreateDIBSection() with a BITMAPINFOHEADER) and call
+ * SkBitmap::installPixels() to point to the same pixels (ppvBits).
+ * Keeps a map from ppvBits -> HBITMAP or HDC.
+ *
+ * On Mac, we might allocate space ourselves, passing it to both
+ * bitmap.setPixels() and CGBitmapContextCreate(). Keeps a map from
+ * data -> CGContextRef.
+ */
+
+class SK_API SkRasterCanvasLayerAllocator {
+public:
+    SkRasterCanvasLayerAllocator();
+    virtual ~SkRasterCanvasLayerAllocator();
+
+    /**
+     * Attempt to allocate a new raster canvas with backing managed by
+     * this object. Returns nullptr on failure. If allocation is successful,
+     * the canvas takes ownership of this allocator.
+     * The optional parameter initialData is implementation-specific
+     * pixel data to be used as or copied into the backing.
+     */
+    sk_sp<SkCanvas> createCanvas(const SkImageInfo& info,
+                                 const SkSurfaceProps& props,
+                                 void* initialData = nullptr);
+
+    /**
+     * Returns the native context for the buffer after making sure that its
+     * clip and transform are in sync between native and Skia representations.
+     * This graphics-system-specific management structure is treated as
+     * opaque.
+     * Should return nullptr if passed nullptr.
+     */
+    virtual void* getNativeContext(void* buffer,
+                                   const SkMatrix& transform,
+                                   const SkIRect& clip_bounds) = 0;
+
+protected:
+    /**
+     * Allocates a buffer with native-context-specific methods.
+     * Takes implementation-specific pointer to initial data.
+     * Sets rowBytes; returns a pointer to raw pixel memory which
+     * must be able to be passed to SkBitmap::installPixels(),
+     * or nullptr on failure.
+     * Also sets |deallocator| to a function which must be called
+     * when this layer is released, with |deallocatorPayload| as its
+     * argument.
+     */
+    virtual void* allocateLayer(const SkImageInfo& info, size_t* rowBytes,
+                                void (**deallocator)(void*),
+                                void** deallocatorPayload,
+                                void* initialData = nullptr) = 0;
+
+    /**
+     * Builds a Skia device by calling allocateLayer().
+     */
+    SkBaseDevice* makeDevice(const SkImageInfo& info,
+                             const SkSurfaceProps& props,
+                             void* initialData = nullptr);
+
+    friend class SkBitmapDevice;  // for makeDevice()
+};
+
+#endif