support external raster handles

draft CL for chrome: https://codereview.chromium.org/2618323005/

BUG=skia:

Change-Id: I5dbcd700818776a9f62f1e10723d2efcc248dc44
Reviewed-on: https://skia-review.googlesource.com/6406
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 86 insertions, 0 deletions

diff --git a/include/core/SkRasterHandleAllocator.h b/include/core/SkRasterHandleAllocator.h
new file mode 100644
index 0000000000..62796cb62a
--- /dev/null
+++ b/include/core/SkRasterHandleAllocator.h
@@ -0,0 +1,86 @@
+/*
+ * 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 SkRasterHandleAllocator_DEFINED
+#define SkRasterHandleAllocator_DEFINED
+
+#include "SkImageInfo.h"
+
+class SkCanvas;
+class SkMatrix;
+
+/**
+ *  If a client wants to control the allocation of raster layers in a canvas, it should subclass
+ *  SkRasterHandleAllocator. This allocator performs two tasks:
+ *      1. controls how the memory for the pixels is allocated
+ *      2. associates a "handle" to a private object that can track the matrix/clip of the SkCanvas
+ *
+ *  This example allocates a canvas, and defers to the allocator to create the base layer.
+ *
+ *      std::unique_ptr<SkCanvas> canvas = SkRasterHandleAllocator::MakeCanvas(
+ *              SkImageInfo::Make(...),
+ *              skstd::make_unique<MySubclassRasterHandleAllocator>(...),
+ *              nullptr);
+ *
+ *  If you have already allocated the base layer (and its handle, release-proc etc.) then you
+ *  can pass those in using the last parameter to MakeCanvas().
+ *
+ *  Regardless of how the base layer is allocated, each time canvas->saveLayer() is called,
+ *  your allocator's allocHandle() will be called.
+ */
+class SK_API SkRasterHandleAllocator {
+public:
+    virtual ~SkRasterHandleAllocator() {}
+
+    // The value that is returned to clients of the canvas that has this allocator installed.
+    typedef void* Handle;
+
+    struct Rec {
+        // When the allocation goes out of scope, this proc is called to free everything associated
+        // with it: the pixels, the "handle", etc. This is passed the pixel address and fReleaseCtx.
+        void    (*fReleaseProc)(void* pixels, void* ctx);
+        void*   fReleaseCtx;    // context passed to fReleaseProc
+        void*   fPixels;        // pixels for this allocation
+        size_t  fRowBytes;      // rowbytes for these pixels
+        Handle  fHandle;        // public handle returned by SkCanvas::accessTopRasterHandle()
+    };
+
+    /**
+     *  Given a requested info, allocate the corresponding pixels/rowbytes, and whatever handle
+     *  is desired to give clients access to those pixels. The rec also contains a proc and context
+     *  which will be called when this allocation goes out of scope.
+     *
+     *  e.g.
+     *      when canvas->saveLayer() is called, the allocator will be called to allocate the pixels
+     *      for the layer. When canvas->restore() is called, the fReleaseProc will be called.
+     */
+    virtual bool allocHandle(const SkImageInfo&, Rec*) = 0;
+
+    /**
+     *  Clients access the handle for a given layer by calling SkCanvas::accessTopRasterHandle().
+     *  To allow the handle to reflect the current matrix/clip in the canvs, updateHandle() is
+     *  is called. The subclass is responsible to update the handle as it sees fit.
+     */
+    virtual void updateHandle(Handle, const SkMatrix&, const SkIRect&) = 0;
+
+    /**
+     *  This creates a canvas which will use the allocator to manage pixel allocations, including
+     *  all calls to saveLayer().
+     *
+     *  If rec is non-null, then it will be used as the base-layer of pixels/handle.
+     *  If rec is null, then the allocator will be called for the base-layer as well.
+     */
+    static std::unique_ptr<SkCanvas> MakeCanvas(std::unique_ptr<SkRasterHandleAllocator>,
+                                                const SkImageInfo&, const Rec* rec = nullptr);
+
+private:
+    friend class SkBitmapDevice;
+
+    Handle allocBitmap(const SkImageInfo&, SkBitmap*);
+};
+
+#endif