Use geometric mean when selecting a mipmap scale
Workaround for anisotropic mipmap quality issues.
R=reed@google.com,robertphillips@google.com
BUG=skia:4863,chromium:586894
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1697423002
Review URL: https://codereview.chromium.org/1697423002
diff --git a/src/core/SkMipMap.cpp b/src/core/SkMipMap.cpp
index 7266dc6..1f69c24 100644
--- a/src/core/SkMipMap.cpp
+++ b/src/core/SkMipMap.cpp
@@ -326,8 +326,16 @@
}
SkASSERT(scaleSize.width() >= 0 && scaleSize.height() >= 0);
+
+#ifndef SK_SUPPORT_LEGACY_ANISOTROPIC_MIPMAP_SCALE
// Use the smallest scale to match the GPU impl.
const SkScalar scale = SkTMin(scaleSize.width(), scaleSize.height());
+#else
+ // Ideally we'd pick the smaller scale, to match Ganesh. But ignoring one of the
+ // scales can produce some atrocious results, so for now we use the geometric mean.
+ // (https://bugs.chromium.org/p/skia/issues/detail?id=4863)
+ const SkScalar scale = SkScalarSqrt(scaleSize.width() * scaleSize.height());
+#endif
if (scale >= SK_Scalar1 || scale <= 0 || !SkScalarIsFinite(scale)) {
return false;