GrTessellator: fix for points which become non-finite on AA stroking.

If input points are near-infinite, they may become inf or NaN when
stroked.  Before converting the results of intersection from double
to float, clamp them to the [-FLT_MAX/FLT_MAX] range.

BUG=798679

Change-Id: I7d61130dd26147a9b7cfd38aa96567e3867b5c3e
Reviewed-on: https://skia-review.googlesource.com/90983
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index 34be6f75e4..3e90046b8f 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -16,6 +16,7 @@
 #include "SkPointPriv.h"
 #include "SkTDPQueue.h"
 
+#include <algorithm>
 #include <stdio.h>
 
 /*
@@ -282,6 +283,10 @@ inline void round(SkPoint* p) {
     p->fY = SkScalarRoundToScalar(p->fY * SkFloatToScalar(4.0f)) * SkFloatToScalar(0.25f);
 }
 
+inline SkScalar double_to_clamped_scalar(double d) {
+    return SkDoubleToScalar(std::min((double) SK_ScalarMax, std::max(d, (double) -SK_ScalarMax)));
+}
+
 // A line equation in implicit form. fA * x + fB * y + fC = 0, for all points (x, y) on the line.
 struct Line {
     Line(double a, double b, double c) : fA(a), fB(b), fC(c) {}
@@ -320,9 +325,9 @@ struct Line {
         if (denom == 0.0) {
             return false;
         }
-        double scale = 1.0f / denom;
-        point->fX = SkDoubleToScalar((fB * other.fC - other.fB * fC) * scale);
-        point->fY = SkDoubleToScalar((other.fA * fC - fA * other.fC) * scale);
+        double scale = 1.0 / denom;
+        point->fX = double_to_clamped_scalar((fB * other.fC - other.fB * fC) * scale);
+        point->fY = double_to_clamped_scalar((other.fA * fC - fA * other.fC) * scale);
         round(point);
         return true;
     }