Ensure SkPictureImageFilter::onFilterImage doesn't double-convert color

Consider the following sequence of events:
1. SkPictureImageFilter::onFilterImage creates a local canvas, wraps it
   in a SkColorSpaceXformCanvas, and passed to...
2. SkPictureImageFilter::drawPictureAtLocalResolution creates a local
   canvas (localCanvas) wraps that in a SkColorSpaceXformCanvas, draws
   the picture to it, doing sRGB->fColorSpace conversion
3. We then call makeImageSnapshot to produce a SkSpecialImage, localImg,
   which is not tagged with any color space.
4. When the draw that localImg to the passed-in SkColorSpaceXformCanvas,
   which then performs sRGB->fColorSpace conversion a second time.

We now have performed color conversion twice.

One fix for this would be to have the image produced by the call to
localSurface->makeImageSnapshot() be tagged with fColorSpace. This is
somewhat involved.

The less invasive fix is to remove the SkColorSpaceXformCanvas in
SkPictureImageFilter::onFilterImage, and push it down into the two
branches, SkPictureImageFilter::drawPictureAtLocalResolution and
SkPictureImageFilter::drawPictureAtDeviceResolution.

BUG=728332

Change-Id: If2aa32e18ad660b3e361f1d90845eeb8555fe404
Reviewed-on: https://skia-review.googlesource.com/18282
Reviewed-by: Matt Sarett <msarett@google.com>
Reviewed-by: Christopher Cameron <ccameron@google.com>
Commit-Queue: Christopher Cameron <ccameron@google.com>

1 files changed, 7 insertions, 9 deletions

diff --git a/src/effects/SkPictureImageFilter.cpp b/src/effects/SkPictureImageFilter.cpp
index 3c59e5e109..2a863542fe 100644
--- a/src/effects/SkPictureImageFilter.cpp
+++ b/src/effects/SkPictureImageFilter.cpp
@@ -131,15 +131,6 @@ sk_sp<SkSpecialImage> SkPictureImageFilter::onFilterImage(SkSpecialImage* source
 
     SkCanvas* canvas = surf->getCanvas();
     SkASSERT(canvas);
-
-    std::unique_ptr<SkCanvas> xformCanvas = nullptr;
-    if (fColorSpace) {
-        // Only non-null in the case where onMakeColorSpace() was called.  This instructs
-        // us to do the color space xform on playback.
-        xformCanvas = SkCreateColorSpaceXformCanvas(canvas, fColorSpace);
-        canvas = xformCanvas.get();
-    }
-
     canvas->clear(0x0);
 
     if (kDeviceSpace_PictureResolution == fPictureResolution ||
@@ -162,6 +153,13 @@ sk_sp<SkImageFilter> SkPictureImageFilter::onMakeColorSpace(SkColorSpaceXformer*
 void SkPictureImageFilter::drawPictureAtDeviceResolution(SkCanvas* canvas,
                                                          const SkIRect& deviceBounds,
                                                          const Context& ctx) const {
+    std::unique_ptr<SkCanvas> xformCanvas = nullptr;
+    if (fColorSpace) {
+        // Only non-null in the case where onMakeColorSpace() was called.  This instructs
+        // us to do the color space xform on playback.
+        xformCanvas = SkCreateColorSpaceXformCanvas(canvas, fColorSpace);
+        canvas = xformCanvas.get();
+    }
     canvas->translate(-SkIntToScalar(deviceBounds.fLeft), -SkIntToScalar(deviceBounds.fTop));
     canvas->concat(ctx.ctm());
     canvas->drawPicture(fPicture);