initial checkin for experimenting

src/core/SkCanvasDrawable.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkCanvasDrawable_DEFINED
+#define SkCanvasDrawable_DEFINED
+
+#include "SkRefCnt.h"
+
+class SkCanvas;
+struct SkRect;
+
+/**
+ *  Base-class to capture a set of drawing commands (sent to SkCanvas). Instances of this class
+ *  need not be thread-safe, but they must be able to be used in a thread different from where
+ *  they were created.
+ */
+class SkCanvasDrawable : public SkRefCnt {

[djsollen, 2014/11/10 19:23:38]

seems that the only real use case for this is animation, but the class name or
comments don't seem to point that out.  Any other use seems like it would be an
abuse of the API.

[reed1, 2014/11/11 12:46:30]

I see it as more general. For instance, it could also be thought of as an
image-generator, much like we have for lazy decoded images. Or as a class to
implement state changes in a UI element (e.g. checked or unchecked).

+public:
+    SkCanvasDrawable();
+
+    /**
+     *  Draws into the specified content. The drawing sequence will be balanced upon return
+     *  (i.e. the saveLevel() on the canvas will match what it was when draw() was called,
+     *  and the current matrix and clip settings will not be changed.
+     */
+    void draw(SkCanvas*);
+
+    /**
+     *  Return a unique value for this instance. If two calls to this return the same value,
+     *  it is presumed that calling the draw() method will render the same thing as well.
+     *
+     *  Subclasses that change their state should call notifyDrawingChanged() to ensure that
+     *  a new value will be returned the next time it is called.
+     */
+    uint32_t getGenerationID();
+
+    /**
+     *  If the drawable knows a bounds that will contains all of its drawing, return true and
+     *  set the parameter to that rectangle. If one is not known, ignore the parameter and
+     *  return false.
+     */
+    bool getBounds(SkRect*);
+
+    void notifyDrawingChanged();

[djsollen, 2014/11/10 19:23:39]

can you add some comments on this?

[reed1, 2014/11/11 12:46:30]

Done.

[djsollen, 2014/11/11 12:53:12]

Did you forget to upload the comments? I don't see them in patch set 3?

+
+protected:
+    virtual void onDraw(SkCanvas*) = 0;

[robertphillips, 2014/11/10 19:16:35]

What do you think about having a default implementation of onGetBounds that just
returns false?

[reed1, 2014/11/10 19:20:03]

Done.

+    virtual bool onGetBounds(SkRect*) = 0;
+
+private:
+    int32_t fGenerationID;
+};
+
+#endif