Bug 781731 - Speed up shadows by using tee surface to avoid doing a read back. r=jrmuizel

content/canvas/src/nsCanvasRenderingContext2DAzure.cpp

@@ -311,7 +311,7 @@ public:
     transform._32 -= mTempRect.y;
       
     mTarget =
-      mCtx->mTarget->CreateSimilarDrawTarget(IntSize(int32_t(mTempRect.width), int32_t(mTempRect.height)),
+      mCtx->mTarget->CreateShadowDrawTarget(IntSize(int32_t(mTempRect.width), int32_t(mTempRect.height)),
                                              FORMAT_B8G8R8A8);
 
     if (!mTarget) {

gfx/2d/2D.h

@@ -727,6 +727,15 @@ public:
   virtual TemporaryRef<DrawTarget>
     CreateSimilarDrawTarget(const IntSize &aSize, SurfaceFormat aFormat) const = 0;
 
+  /*
+   * Create a draw target optimized for drawing a shadow.
+   */
+  virtual TemporaryRef<DrawTarget>
+    CreateShadowDrawTarget(const IntSize &aSize, SurfaceFormat aFormat) const
+  {
+    return CreateSimilarDrawTarget(aSize, aFormat);
+  }
+
   /*
    * Create a path builder with the specified fillmode.
    *

gfx/2d/DrawTargetCairo.cpp

@@ -11,6 +11,7 @@
 #include "ScaledFontBase.h"
 
 #include "cairo.h"
+#include "cairo-tee.h"
 #include <string.h>
 
 #include "Blur.h"
@@ -391,19 +392,11 @@ DrawTargetCairo::DrawSurfaceWithShadow(SourceSurface *aSurface,
   Float height = aSurface->GetSize().height;
  
   SourceSurfaceCairo* source = static_cast<SourceSurfaceCairo*>(aSurface);
-  cairo_surface_t* surf = source->GetSurface();
- 
-  cairo_surface_t* blursurf = cairo_image_surface_create(CAIRO_FORMAT_A8,
-                                                         width,
-                                                         height);
-
-  cairo_t* ctx = cairo_create(blursurf);
-  cairo_set_source_surface(ctx, surf, 0, 0);
-  cairo_new_path(ctx);
-  cairo_rectangle(ctx, 0, 0, width, height);
-  cairo_fill(ctx);
-  cairo_destroy(ctx);
+  cairo_surface_t* sourcesurf = source->GetSurface();
+  cairo_surface_t* blursurf = cairo_tee_surface_index(sourcesurf, 0);
+  cairo_surface_t* surf = cairo_tee_surface_index(sourcesurf, 1);
  
+  MOZ_ASSERT(cairo_surface_get_type(blursurf) == CAIRO_SURFACE_TYPE_IMAGE);
   Rect extents(0, 0, width, height);
   AlphaBoxBlur blur(cairo_image_surface_get_data(blursurf),
                     extents,
@@ -444,7 +437,6 @@ DrawTargetCairo::DrawSurfaceWithShadow(SourceSurface *aSurface,
   }
 
   cairo_restore(mContext);
-  cairo_surface_destroy(blursurf);
 }
 
 void
@@ -799,6 +791,40 @@ DrawTargetCairo::InitAlreadyReferenced(cairo_surface_t* aSurface, const IntSize&
   return true;
 }
 
+TemporaryRef<DrawTarget>
+DrawTargetCairo::CreateShadowDrawTarget(const IntSize &aSize, SurfaceFormat aFormat) const
+{
+  cairo_surface_t* similar = cairo_surface_create_similar(cairo_get_target(mContext),
+                                                          GfxFormatToCairoContent(aFormat),
+                                                          aSize.width, aSize.height);
+
+  if (cairo_surface_status(similar)) {
+    return nullptr;
+  }
+
+  cairo_surface_t* blursurf = cairo_image_surface_create(CAIRO_FORMAT_A8,
+                                                         aSize.width,
+                                                         aSize.height);
+
+  if (cairo_surface_status(blursurf)) {
+    return nullptr;
+  }
+
+  cairo_surface_t* tee = cairo_tee_surface_create(blursurf);
+  cairo_surface_destroy(blursurf);
+  if (cairo_surface_status(tee)) {
+    cairo_surface_destroy(similar);
+    return nullptr;
+  }
+
+  cairo_tee_surface_add(tee, similar);
+  cairo_surface_destroy(similar);
+
+  RefPtr<DrawTargetCairo> target = new DrawTargetCairo();
+  target->InitAlreadyReferenced(tee, aSize);
+  return target;
+}
+
 bool
 DrawTargetCairo::Init(cairo_surface_t* aSurface, const IntSize& aSize)
 {

gfx/2d/DrawTargetCairo.h

@@ -115,6 +115,8 @@ public:
     CreateSourceSurfaceFromNativeSurface(const NativeSurface &aSurface) const;
   virtual TemporaryRef<DrawTarget>
     CreateSimilarDrawTarget(const IntSize &aSize, SurfaceFormat aFormat) const;
+  virtual TemporaryRef<DrawTarget>
+    CreateShadowDrawTarget(const IntSize &aSize, SurfaceFormat aFormat) const;
 
   virtual TemporaryRef<GradientStops>
     CreateGradientStops(GradientStop *aStops,