[WIP] Add Context to SkDrawLooper.

include/core/SkDrawLooper.h

 
 /*
  * Copyright 2011 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkDrawLooper_DEFINED
 #define SkDrawLooper_DEFINED
 
 #include "SkFlattenable.h"
 
+#define kDrawLooperContextStorageLongCount    (sizeof(void*) + sizeof(int))

[Dominik Grewe, 2014/02/07 11:57:15]

It's not particularly nice to hardcode the size of the largest DrawContext
subclass, but I'm not sure if we want to include the header for that class here
(and the class is currently private).

[reed1, 2014/02/07 14:46:02]

1. I think callers have to be able to survive subclasses that require more
storage than we provided.
2. I agree that I *don't* want to make any public promises about the max-size of
internal subclasses.

I vote to remove this define.

[Dominik Grewe, 2014/02/07 16:59:17]

I'll move it into the cpp files instead.

+
 class SkCanvas;
 class SkPaint;
 struct SkRect;
 class SkString;
 
 /** \class SkDrawLooper
     Subclasses of SkDrawLooper can be attached to a SkPaint. Where they are,
     and something is drawn to a canvas with that paint, the looper subclass will
     be called, allowing it to modify the canvas and/or paint for that draw call.
     More than that, via the next() method, the looper can modify the draw to be
     invoked multiple times (hence the name loop-er), allow it to perform effects
     like shadows or frame/fills, that require more than one pass.
 */
 class SK_API SkDrawLooper : public SkFlattenable {
 public:
     SK_DECLARE_INST_COUNT(SkDrawLooper)
 
     /**
-     *  Called right before something is being drawn. This will be followed by
-     *  calls to next() until next() returns false.
+     *  Holds state during a draw. Users call next() until it returns false. The
+     *  final call to next() will also delete the context.
+     *
+     *  Subclasses of SkDrawLooper should create a subclass of this object to
+     *  hold state specific to their subclass.
      */
-    virtual void init(SkCanvas*) = 0;
+    class SK_API DrawContext {
+    public:
+        DrawContext() {}
+        virtual ~DrawContext() {}
+
+        /**
+         *  Called in a loop (after init()). Each time true is returned, the
+         *  object is drawn (possibly with a modified canvas and/or paint). When
+         *  false is finally returned, drawing for the object stops. When the
+         *  context is no longer in use, call cleanup().
+         *
+         *  On each call, the paint will be in its original state, but the
+         *  canvas will be as it was following the previous call to next() or
+         *  init().
+         *
+         *  The implementation must ensure that, when next() finally returns
+         *  false, that the canvas has been restored to the state it was
+         *  initially, before init() was first called.
+         */
+        virtual bool next(SkCanvas* canvas, SkPaint* paint) = 0;
+
+        void cleanup(void* storage);

[Dominik Grewe, 2014/02/07 11:57:15]

I've added this so the user is in charge of when to free the memory. This is
required for canComputeFastBounds below, which may finish before next() returns
false.

+    };
 
     /**
-     *  Called in a loop (after init()). Each time true is returned, the object
-     *  is drawn (possibly with a modified canvas and/or paint). When false is
-     *  finally returned, drawing for the object stops.
+     *  Called right before something is being drawn. Returns a DrawContext
+     *  whose next() method should be called until it returns false.
      *
-     *  On each call, the paint will be in its original state, but the canvas
-     *  will be as it was following the previous call to next() or init().
-     *
-     *  The implementation must ensure that, when next() finally returns false,
-     *  that the canvas has been restored to the state it was initially, before
-     *  init() was first called.
+     *  Pass a pointer to pre-allocated memory to avoid dynamic memory
+     *  allocation.
      */
-    virtual bool next(SkCanvas*, SkPaint* paint) = 0;
+    virtual DrawContext* init(SkCanvas*, void* storage, size_t storageSize)
+        const = 0;
+
 
     /**
      * The fast bounds functions are used to enable the paint to be culled early
      * in the drawing pipeline. If a subclass can support this feature it must
      * return true for the canComputeFastBounds() function.  If that function
      * returns false then computeFastBounds behavior is undefined otherwise it
      * is expected to have the following behavior. Given the parent paint and
      * the parent's bounding rect the subclass must fill in and return the
      * storage rect, where the storage rect is with the union of the src rect
      * and the looper's bounding rect.
      */
     virtual bool canComputeFastBounds(const SkPaint& paint);
     virtual void computeFastBounds(const SkPaint& paint,
                                    const SkRect& src, SkRect* dst);
 
     SkDEVCODE(virtual void toString(SkString* str) const = 0;)
     SK_DEFINE_FLATTENABLE_TYPE(SkDrawLooper)
 
 protected:
     SkDrawLooper() {}
     SkDrawLooper(SkReadBuffer& buffer) : INHERITED(buffer) {}
 
 private:
     typedef SkFlattenable INHERITED;
 };
 
 #endif