Add sk_sp helpers and switch Blink SkShader clients to the new APIs

third_party/WebKit/Source/platform/graphics/skia/SkiaUtils.h

 /*
  * Copyright (c) 2006,2007,2008, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 20 matching lines @@
 // All of the functions in this file should move to new homes and this file should be deleted.
 
 #ifndef SkiaUtils_h
 #define SkiaUtils_h
 
 #include "platform/PlatformExport.h"
 #include "platform/graphics/GraphicsTypes.h"
 #include "platform/graphics/Image.h"
 #include "platform/transforms/AffineTransform.h"
 #include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkRefCnt.h"
 #include "wtf/MathExtras.h"
 
 namespace blink {
 
 class GraphicsContext;
 
 SkXfermode::Mode PLATFORM_EXPORT WebCoreCompositeToSkiaComposite(CompositeOperator, WebBlendMode = WebBlendModeNormal);
 CompositeOperator PLATFORM_EXPORT compositeOperatorFromSkia(SkXfermode::Mode);
 WebBlendMode PLATFORM_EXPORT blendModeFromSkia(SkXfermode::Mode);
 
@@ skipping 68 matching lines @@
 void drawPlatformFocusRing(const PrimitiveType&, SkCanvas*, SkColor, int width);
 
 // TODO(fmalita): remove in favor of direct SrcRectConstraint use.
 inline SkCanvas::SrcRectConstraint WebCoreClampingModeToSkiaRectConstraint(Image::ImageClampingMode clampMode)
 {
     return clampMode == Image::ClampImageToSourceRect
         ? SkCanvas::kStrict_SrcRectConstraint
         : SkCanvas::kFast_SrcRectConstraint;
 }
 
+// Skia's smart pointer APIs are preferable over their legacy raw pointer counterparts.
+// The following helpers ensure interoperability between Skia's SkRefCnt wrapper sk_sp<T> and
+// Blink's RefPtr<T>/PassRefPtr<T>.
+//
+//   - adoptSkSp(sk_sp<T>):      adopts an sk_sp into a PassRefPtr (to be used when transferring
+//                               ownership from Skia to Blink).
+//   - toSkSp(PassRefPtr<T>):    releases a PassRefPtr into a sk_sp (to be used when transferring
+//                               ownership from Blink to Skia).
+//   - toSkSp(const RefPtr<T>&): shares a RefPtr as a new sk_sp (to be used when sharing
+//                               ownership).
+//
+// General guidelines
+//
+// When receiving ref counted objects from Skia:
+//
+//   1) use sk_sp-based Skia factories if available (e.g. SkShader::MakeFoo() instead of
+//      SkShader::CreateFoo())
+//
+//   2) use sk_sp<T> locals for temporary objects (to be immediately transferred back to Skia)
+//
+//   3) use RefPtr<T>/PassRefPtr<T> for objects to be retained in Blink, use
+//      adoptSkSp(sk_sp<T>) to convert
+//
+// When passing ref counted objects to Skia:
+//
+//   1) use sk_sk-based Skia APIs when available (e.g. SkPaint::setShader(sk_sp<SkShader>)
+//      instead of SkPaint::setShader(SkShader*))
+//
+//   2) if the object ownership is being passed to Skia, use std::move(sk_sp<T>) or
+//      toSkSp(PassRefPtr<T>) to transfer without refcount churn
+//
+//   3) if the object ownership is shared with Skia (Blink retains a reference), use
+//      toSkSp(const RefPtr<T>&)
+//
+// Example (creating a SkShader and setting it on SkPaint):
+//
+// a) legacy/old style
+//
+//     RefPtr<SkShader> shader = adoptRef(SkShader::CreateFoo(...));
+//     paint.setShader(shader.get());
+//
+//  (Note: the legacy approach introduces refcount churn as Skia grabs a ref while Blink is
+//   temporarily holding on to its own)
+//
+// b) new style, ownership transferred
+//
+//     // using Skia smart pointer locals
+//     sk_sp<SkShader> shader = SkShader::MakeFoo(...);
+//     paint.setShader(std::move(shader));
+//
+//     // using Blink smart pointer locals
+//     RefPtr<SkShader> shader = adoptSkSp(SkShader::MakeFoo(...));
+//     paint.setShader(toSkSp(shader.release());
+//
+//     // using no locals
+//     paint.setShader(SkShader::MakeFoo(...));
+//
+// c) new style, shared ownership
+//
+//     RefPtr<SkShader> m_shader = adoptSkSp(SkShader::MakeFoo(...));

[jbroman, 2016/03/17 17:19:13]

super-nit: maybe remove m_ as this doesn't look like it's a member in this
example?

[f(malita), 2016/03/17 18:04:42]

Done.

+//     paint.setShader(toSkSp(m_shader));
+//
+template <typename T> PassRefPtr<T> adoptSkSp(sk_sp<T> sp)
+{
+    return adoptRef(sp.release());
+}
+
+template <typename T> sk_sp<T> toSkSp(PassRefPtr<T> ref)
+{
+    return sk_sp<T>(ref.leakRef());
+}
+
+template <typename T> sk_sp<T> toSkSp(const RefPtr<T>& ref)
+{
+    return toSkSp(PassRefPtr<T>(ref));
+}
+
 } // namespace blink
 
 #endif  // SkiaUtils_h