allow div-by-zero in shadow utils

Bug: oss-fuzz:6665
Change-Id: I5cbe02bf574d849340c85c0964d92ece45daac1f
Reviewed-on: https://skia-review.googlesource.com/129932
Commit-Queue: Mike Reed <reed@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Auto-Submit: Mike Reed <reed@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>

1 files changed, 10 insertions, 3 deletions

diff --git a/src/core/SkDrawShadowInfo.h b/src/core/SkDrawShadowInfo.h
index da63a08104..d5820919ea 100644
--- a/src/core/SkDrawShadowInfo.h
+++ b/src/core/SkDrawShadowInfo.h
@@ -30,6 +30,13 @@ namespace SkDrawShadowMetrics {
 static constexpr auto kAmbientHeightFactor = 1.0f / 128.0f;
 static constexpr auto kAmbientGeomFactor = 64.0f;
 
+static inline float divide_and_pin(float numer, float denom, float min, float max) {
+    float result = SkTPin(sk_ieee_float_divide(numer, denom), min, max);
+    // ensure that SkTPin handled non-finites correctly
+    SkASSERT(result >= min && result <= max);
+    return result;
+}
+
 inline SkScalar AmbientBlurRadius(SkScalar height) {
     return height*kAmbientHeightFactor*kAmbientGeomFactor;
 }
@@ -39,15 +46,15 @@ inline SkScalar AmbientRecipAlpha(SkScalar height) {
 }
 
 inline SkScalar SpotBlurRadius(SkScalar occluderZ, SkScalar lightZ, SkScalar lightRadius) {
-    return lightRadius*SkTPin(occluderZ / (lightZ - occluderZ), 0.0f, 0.95f);
+    return lightRadius*divide_and_pin(occluderZ, lightZ - occluderZ, 0.0f, 0.95f);
 }
 
 inline void GetSpotParams(SkScalar occluderZ, SkScalar lightX, SkScalar lightY, SkScalar lightZ,
                           SkScalar lightRadius,
                           SkScalar* blurRadius, SkScalar* scale, SkVector* translate) {
-    SkScalar zRatio = SkTPin(occluderZ / (lightZ - occluderZ), 0.0f, 0.95f);
+    SkScalar zRatio = divide_and_pin(occluderZ, lightZ - occluderZ, 0.0f, 0.95f);
     *blurRadius = lightRadius*zRatio;
-    *scale = SkTPin(lightZ / (lightZ - occluderZ), 1.0f, 1.95f);
+    *scale = divide_and_pin(lightZ, lightZ - occluderZ, 1.0f, 1.95f);
     *translate = SkVector::Make(-zRatio * lightX, -zRatio * lightY);
 }