Implement intra-frame cacheing in image filters.

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 27b7a4c804222604d5ad2086e1bcd8481786b75f..8704de21dece27ef3548a748c5c17a5a6b563ef1 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -1258,7 +1258,9 @@ void SkCanvas::internalDrawDevice(SkBaseDevice* srcDev, int x, int y,
             SkMatrix matrix = *iter.fMatrix;
             matrix.postTranslate(SkIntToScalar(-pos.x()), SkIntToScalar(-pos.y()));
             SkIRect clipBounds = SkIRect::MakeWH(srcDev->width(), srcDev->height());
-            SkImageFilter::Context ctx(matrix, clipBounds);
+            SkImageFilter::Cache* cache = SkImageFilter::Cache::Create(2);

[reed1, 2014/04/10 21:23:26]

That '2' is mysterious to the new reviewer...

1. Why is 2 a good answer?

2. How about...

const int minChildren = 2; // answer to #1
cache = SkImageFilter::Cache::Create(minChildren);

[Stephen White, 2014/04/10 21:26:36]

2 means "cache only image filters with 2 or more children".

(In an upcoming change, I'm going to reuse this class externally with a value
other than 2.)
How about I make it the default param?

+            SkAutoUnref aur(cache);
+            SkImageFilter::Context ctx(matrix, clipBounds, cache);
             if (filter->filterImage(&proxy, src, ctx, &dst, &offset)) {
                 SkPaint tmpUnfiltered(*paint);
                 tmpUnfiltered.setImageFilter(NULL);
@@ -1298,7 +1300,9 @@ void SkCanvas::drawSprite(const SkBitmap& bitmap, int x, int y,
             SkMatrix matrix = *iter.fMatrix;
             matrix.postTranslate(SkIntToScalar(-pos.x()), SkIntToScalar(-pos.y()));
             SkIRect clipBounds = SkIRect::MakeWH(bitmap.width(), bitmap.height());
-            SkImageFilter::Context ctx(matrix, clipBounds);
+            SkImageFilter::Cache* cache = SkImageFilter::Cache::Create(2);
+            SkAutoUnref aur(cache);
+            SkImageFilter::Context ctx(matrix, clipBounds, cache);
             if (filter->filterImage(&proxy, bitmap, ctx, &dst, &offset)) {
                 SkPaint tmpUnfiltered(*paint);
                 tmpUnfiltered.setImageFilter(NULL);