do reject vertical lines if they are outside of the clip

Bug: skia:7981
Change-Id: Icae11ac2934bc6db5a5c3ad0f17aaf615efa2fe5
Reviewed-on: https://skia-review.googlesource.com/149291
Auto-Submit: Mike Reed <reed@google.com>
Commit-Queue: Cary Clark <caryclark@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>

src/core/SkLineClipper.cpp

@@ -137,10 +137,12 @@ bool SkLineClipper::IntersectLine(const SkPoint src[2], const SkRect& clip,
     }
 
     // check for quick-reject in X again, now that we may have been chopped
-    if ((tmp[index1].fX <= clip.fLeft || tmp[index0].fX >= clip.fRight) &&
-        tmp[index0].fX < tmp[index1].fX) {
-        // only reject if we have a non-zero width
-        return false;
+    if ((tmp[index1].fX <= clip.fLeft || tmp[index0].fX >= clip.fRight)) {
+        // usually we will return false, but we don't if the line is vertical and coincident
+        // with the clip.
+        if (tmp[0].fX != tmp[1].fX || tmp[0].fX < clip.fLeft || tmp[0].fX > clip.fRight) {
+            return false;
+        }
     }
 
     if (tmp[index0].fX < clip.fLeft) {

tests/ClipperTest.cpp

@@ -156,3 +156,14 @@ DEF_TEST(Clipper, reporter) {
     test_edgeclipper();
     test_hairclipping(reporter);
 }
+
+#include "SkLineClipper.h"
+
+DEF_TEST(LineClipper_skbug_7981, r) {
+    SkPoint src[] = {{ -5.77698802E+17f, -1.81758057E+23f}, {38127, 2}};
+    SkPoint dst[2];
+    SkRect clip = { -32767, -32767, 32767, 32767 };
+
+    SkLineClipper::IntersectLine(src, clip, dst);
+}
+