Create a semi-stable API for capturing the state of an SkCanvas and reconstructing that state acros…

include/utils/SkCanvasStateUtils.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkCanvasStateUtils_DEFINED
+#define SkCanvasStateUtils_DEFINED
+
+#include "SkCanvas.h"
+
+class SkCanvasState;
+
+/**
+ * A set of functions that are useful for copying an SkCanvas across a library
+ * boundary where the Skia libraries on either side of the boundary may not be
+ * version identical.  The expected usage is outline below...
+ *
+ *                          Lib Boundary
+ * CaptureCanvasState(...)      |||
+ *   SkCanvas --> SkCanvasState |||
+ *                              ||| CreateFromCanvasState(...)
+ *                              |||   SkCanvasState --> SkCanvas`
+ *                              ||| Draw into SkCanvas`
+ *                              ||| Unref SkCanvas`
+ * ReleaseCanvasState(...)      |||
+ *
+ */
+namespace SkCanvasStateUtils {
+    /**
+     * Captures the current state of the canvas into an opaque ptr that is safe
+     * to pass between different instances of Skia (which may or may not be the
+     * same version). The function will return NULL in the event that one of the
+     * following conditions are true.
+     *  1) the canvas device type is not supported (currently only raster is supported)
+     *  2) the canvas clip type is not supported (currently only non-AA clips are supported)
+     *
+     * It is recommended that the original canvas also not be used until all
+     * canvases that have been created using its captured state have been dereferenced.
+     *
+     * Finally, it is important to note that any draw filters attached to the
+     * canvas are NOT currently captured.
+     *
+     * @param canvas The canvas you wish to capture the current state of.
+     * @return NULL or an opaque ptr that can be passed to CreateFromCanvasState
+     *         to reconstruct the canvas. The caller is responsible for calling
+     *         ReleaseCanvasState to free the memory associated with this state.
+     */
+    SK_API SkCanvasState* CaptureCanvasState(SkCanvas* canvas);
+
+    /**
+     * Create a new SkCanvas from the captured state of another SkCanvas. The
+     * function will return NULL in the event that one of the
+     * following conditions are true.
+     *  1) the captured state is in an unrecognized format
+     *  2) the captured canvas device type is not supported
+     *
+     * @param canvas The canvas you wish to capture the current state of.
+     * @return NULL or an SkCanvas* whose devices and matrix/clip state are
+     *         identical to the captured canvas. The caller is responsible for
+     *         calling unref on the SkCanvas.
+     */
+    SK_API SkCanvas* CreateFromCanvasState(const SkCanvasState* state);
+
+    /**
+     * Free the memory associated with the captured canvas state.  The state
+     * should not be released until all SkCanvas objects created using that
+     * state have been dereferenced.
+     *
+     * @param state The captured state you wish to dispose of.
+     */
+    SK_API void ReleaseCanvasState(SkCanvasState* state);
+};
+
+#endif