Correctly handle empty outer blurs.

Most blur styles approach the original mask as the sigma goes to zero.
The outer style however approaches nothing as the mask sigma goes to
zero. Handle this case correctly.

Change-Id: I14f76e144d7cfc78aeaff30ff5444a21f1e5f98b
Reviewed-on: https://skia-review.googlesource.com/128006
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>

1 files changed, 10 insertions, 2 deletions

diff --git a/src/core/SkBlurMask.cpp b/src/core/SkBlurMask.cpp
index f4fa100961..0e0d261903 100644
--- a/src/core/SkBlurMask.cpp
+++ b/src/core/SkBlurMask.cpp
@@ -110,9 +110,17 @@ bool SkBlurMask::BoxBlur(SkMask* dst, const SkMask& src, SkScalar sigma, SkBlurS
         return false;
     }
 
-
     SkMaskBlurFilter blurFilter{sigma, sigma};
-    if (blurFilter.hasNoBlur() && style != kOuter_SkBlurStyle) {
+    if (blurFilter.hasNoBlur()) {
+        // If there is no effective blur most styles will just produce the original mask.
+        // However, kOuter_SkBlurStyle will produce an empty mask.
+        if (style == kOuter_SkBlurStyle) {
+            dst->fImage = nullptr;
+            dst->fBounds = SkIRect::MakeEmpty();
+            dst->fRowBytes = dst->fBounds.width();
+            dst->fFormat = SkMask::kA8_Format;
+            return true;
+        }
         return false;
     }
     const SkIPoint border = blurFilter.blur(src, dst);