abort blur if the sigma is too small

Bug: oss-fuzz:6375
Change-Id: I8f21ea05b44f2ed6fdcdfe2573ac9415f238d833
Reviewed-on: https://skia-review.googlesource.com/107784
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Herb Derby <herb@google.com>

1 files changed, 33 insertions, 0 deletions

diff --git a/tests/BlurTest.cpp b/tests/BlurTest.cpp
index d8d917fe8f..29c44d7886 100644
--- a/tests/BlurTest.cpp
+++ b/tests/BlurTest.cpp
@@ -10,6 +10,7 @@
 #include "SkBlurDrawLooper.h"
 #include "SkCanvas.h"
 #include "SkColorFilter.h"
+#include "SkColorPriv.h"
 #include "SkEmbossMaskFilter.h"
 #include "SkLayerDrawLooper.h"
 #include "SkMaskFilterBase.h"
@@ -669,3 +670,35 @@ DEF_TEST(EmbossPerlinCrash, reporter) {
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////
+#include "SkSurface.h"
+#include "sk_pixel_iter.h"
+
+DEF_TEST(BlurZeroSigma, reporter) {
+    auto surf = SkSurface::MakeRasterN32Premul(20, 20);
+    SkPaint paint;
+    paint.setAntiAlias(true);
+
+    const SkIRect ir = { 5, 5, 15, 15 };
+    const SkRect r = SkRect::Make(ir);
+
+    const SkScalar sigmas[] = { 0, SkBits2Float(1) };
+    // if sigma is zero (or nearly so), we need to draw correctly (unblurred) and not crash
+    // or assert.
+    for (auto sigma : sigmas) {
+        paint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle, sigma));
+        surf->getCanvas()->drawRect(r, paint);
+
+        sk_tool_utils::PixelIter iter(surf.get());
+        SkIPoint  loc;
+        while (const SkPMColor* p = (const SkPMColor*)iter.next(&loc)) {
+            if (ir.contains(loc.fX, loc.fY)) {
+                // inside the rect we draw (opaque black)
+                REPORTER_ASSERT(reporter, *p == SkPackARGB32(0xFF, 0, 0, 0));
+            } else {
+                // outside the rect we didn't draw at all, no blurred edges
+                REPORTER_ASSERT(reporter, *p == 0);
+            }
+        }
+    }
+}
+