Image filters: fix crop rect application in SkXfermodeImageFilter.

The crop rect was being incorrectly applied in SkXfermodeImageFilter:
the background and foreground bounds were having the crop rect applied
individually to them, and then unioned. The correct approach is to take
the union of their bounds, and apply the crop rect to that. (A similar
bug in SkMergeImageFilter was fixed a while back.)

This is important when applying a compositing mode
which affects pixels outside the foreground bounds
(e.g., SrcIn, SrcOut).

NOTE: this will change the results of the xfermodeimagefilter GM (new
test case).
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1842033005

Review URL: https://codereview.chromium.org/1842033005

1 files changed, 7 insertions, 15 deletions

diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index 3b186039d0..db0b5e59bb 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -64,21 +64,13 @@ bool SkXfermodeImageFilter::onFilterImageDeprecated(Proxy* proxy,
         foreground.reset();
     }
 
-    SkIRect bounds, foregroundBounds;
-    SkIRect foregroundSrcBounds = foreground.bounds();
-    foregroundSrcBounds.offset(foregroundOffset);
-    if (!applyCropRect(ctx, foregroundSrcBounds, &foregroundBounds)) {
-        foregroundBounds.setEmpty();
-        foreground.reset();
-    }
-    SkIRect backgroundSrcBounds = background.bounds();
-    backgroundSrcBounds.offset(backgroundOffset);
-    if (!applyCropRect(ctx, backgroundSrcBounds, &bounds)) {
-        bounds.setEmpty();
-        background.reset();
-    }
-    bounds.join(foregroundBounds);
-    if (bounds.isEmpty()) {
+    SkIRect foregroundBounds = foreground.bounds();
+    foregroundBounds.offset(foregroundOffset);
+    SkIRect srcBounds = background.bounds();
+    srcBounds.offset(backgroundOffset);
+    srcBounds.join(foregroundBounds);
+    SkIRect bounds;
+    if (!this->applyCropRect(ctx, srcBounds, &bounds)) {
         return false;
     }