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..e1544c52db4df894acce69c19114e9e8ca14fd75
--- /dev/null
+++ b/include/core/SkRasterCanvasLayerAllocator.h
@@ -0,0 +1,90 @@
+/*
+ * 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 "SkSurfaceProps.h"
+#include "SkRefCnt.h"
+
+class SkCanvas;
+class SkPaint;
+
+/**
+ * Base class to encapsulate platform-specific bitmap allocations.
+ *
+ * TBD: in subclass destructors do we expect them to tear down
+ * all the bitmaps and contexts they've set up that haven't already
+ * been freed?
+ *
+ * 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.
+ *
+ * On Mac, we might allocate space ourselves, passing it to both
+ * bitmap.setPixels() and CGBitmapContextCreate(). Keeps a map from
+ * data -> CGContextRef.
+ */
+
+class SkRasterCanvasLayerAllocator : public SkRefCnt {
+public:
+    SkRasterCanvasLayerAllocator();
+    virtual ~SkRasterCanvasLayerAllocator();
+
+    /**
+     * Attempt to allocate a new raster canvas with backing managed by
+     * this object. Returns nullptr on failure.
+     * TODO(tomhudson): is this the correct place to insert initialData?
+     */
+    SkCanvas* CreateCanvas(const SkImageInfo& info,

[f(malita), 2016/09/16 13:39:01]

nit: non-static -> "createCanvas()"?

Also, would it make sense to return a sk_sp<SkCanvas> instead of raw ptr?

[tomhudson, 2016/09/28 21:23:57]

Done.

Although it's really a weird member function, since it returns a thing that
takes unique ownership of the object. There's probably a saner way of
constructing these things.

+                           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.

[reed1, 2016/09/16 13:15:00]

// What is "buffer"?

I wonder if it would help document things if we had some alias types...

typedef void* NativeContext;
typedef void* LayerBuffer;  // not sure what to name this guy

+     * 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;
+
+    /**
+     * Perform any OS-dependent synchronization necessary to

[reed1, 2016/09/16 13:15:00]

// When is this called?

[tomhudson, 2016/09/28 21:23:57]

Acknowledged.

+     * guarantee that both Skia and the backing agree on the
+     * state of all pixels.
+     */
+    virtual void flush(void* buffer) = 0;
+
+    /**
+     * Cleans up as necessary an allocated buffer and its matching
+     * native context.

[reed1, 2016/09/16 13:15:00]

// When is this called?

[tomhudson, 2016/09/28 21:23:57]

Acknowledged.

+     */
+    virtual void free(void* buffer) = 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.
+     */
+    virtual void* allocateLayer(const SkImageInfo& info, size_t* rowBytes,
+                                void* initialData = nullptr) = 0;
+
+    friend class SkBitmapDevice;
+};
+
+#endif