Add some additional checks for shadow generation

Change-Id: I4dae4173ad879827e4e1fa3ad12aa0447d1df252
Reviewed-on: https://skia-review.googlesource.com/110360
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

include/core/SkPoint3.h

@@ -107,6 +107,24 @@ struct SK_API SkPoint3 {
         fZ -= v.fZ;
     }
 
+    /** Returns true if fX, fY, and fZ are measurable values.
+
+     @return  true for values other than infinities and NaN
+     */
+    bool isFinite() const {
+        SkScalar accum = 0;
+        accum *= fX;
+        accum *= fY;
+        accum *= fZ;
+
+        // accum is either NaN or it is finite (zero).
+        SkASSERT(0 == accum || SkScalarIsNaN(accum));
+
+        // value==value will be true iff value is not NaN
+        // TODO: is it faster to say !accum or accum==accum?
+        return !SkScalarIsNaN(accum);
+    }
+
     /** Returns the dot product of a and b, treating them as 3D vectors
     */
     static SkScalar DotProduct(const SkPoint3& a, const SkPoint3& b) {

src/utils/SkShadowTessellator.cpp

@@ -177,6 +177,12 @@ void SkBaseShadowTessellator::handleLine(const SkMatrix& m, SkPoint* p) {
 
 void SkBaseShadowTessellator::handleQuad(const SkPoint pts[3]) {
 #if SK_SUPPORT_GPU
+    // check for degeneracy
+    SkVector v0 = pts[1] - pts[0];
+    SkVector v1 = pts[2] - pts[0];
+    if (SkScalarNearlyZero(v0.cross(v1))) {
+        return;
+    }
     // TODO: Pull PathUtils out of Ganesh?
     int maxCount = GrPathUtils::quadraticPointCount(pts, kQuadTolerance);
     fPointBuffer.setReserve(maxCount);
@@ -277,7 +283,7 @@ bool SkBaseShadowTessellator::setTransformedHeightFunc(const SkMatrix& ctm) {
         };
     } else {
         SkMatrix ctmInverse;
-        if (!ctm.invert(&ctmInverse)) {
+        if (!ctm.invert(&ctmInverse) || !ctmInverse.isFinite()) {
             return false;
         }
         // multiply by transpose

src/utils/SkShadowUtils.cpp

@@ -535,6 +535,11 @@ void SkShadowUtils::DrawShadow(SkCanvas* canvas, const SkPath& path, const SkPoi
     canvas->private_draw_shadow_rec(path, rec);
 }
 
+static bool validate_rec(const SkDrawShadowRec& rec) {
+    return rec.fLightPos.isFinite() && rec.fZPlaneParams.isFinite() &&
+           SkScalarIsFinite(rec.fLightRadius);
+}
+
 void SkBaseDevice::drawShadow(const SkPath& path, const SkDrawShadowRec& rec) {
     auto drawVertsProc = [this](const SkVertices* vertices, SkBlendMode mode, const SkPaint& paint,
                                 SkScalar tx, SkScalar ty) {
@@ -543,6 +548,10 @@ void SkBaseDevice::drawShadow(const SkPath& path, const SkDrawShadowRec& rec) {
         this->drawVertices(vertices, mode, paint);
     };
 
+    if (!validate_rec(rec)) {
+        return;
+    }
+
     SkMatrix viewMatrix = this->ctm();
     SkAutoDeviceCTMRestore adr(this, SkMatrix::I());