fix pathops fuzz failures

If a curve has the identical start and control points, the
initial or final tangent can't be trivally determined. The
perpendicular to the tangent is used to measure coincidence.

Add logic for cubics, quadratics, and conics, to use the
secondary control points or the end points if the initial
control point alone can't determine the tangent.

Add debugging (currently untriggered by exhaustive testing)
to detect zero-length tangents which are not at the curve
endpoints.

Increase the number of temporary intersecions gathered from
10 to 12 but reduce the max passed in by cubic intersection from
27 to 12. Also, add checks if the max passed exceeds the
storage allocated.

When cleaning up parallel lines, choose the intersection which
is on the end of both segments over the intersection which
is on the end of a single segment.

TBR=reed@google.com
BUG=425140,516266

Review URL: https://codereview.chromium.org/1288863004

1 files changed, 13 insertions, 1 deletions

diff --git a/tests/PathOpsOpTest.cpp b/tests/PathOpsOpTest.cpp
index 637bd042d2..fbe0116eb5 100644
--- a/tests/PathOpsOpTest.cpp
+++ b/tests/PathOpsOpTest.cpp
@@ -5153,13 +5153,25 @@ static void cubics45u(skiatest::Reporter* reporter, const char* filename) {
     testPathOp(reporter, path, pathB, kUnion_SkPathOp, filename);
 }
 
+static void fuzz38(skiatest::Reporter* reporter, const char* filename) {
+    SkPath path, pathB;
+    path.moveTo(100.34f, 303.312f);
+    path.lineTo(-1e+08, 303.312f);
+    path.lineTo(102, 310.156f);
+    path.lineTo(100.34f, 310.156f);
+    path.lineTo(100.34f, 303.312f);
+    path.close();
+    testPathOpCheck(reporter, path, pathB, kUnion_SkPathOp, filename, FLAGS_runFail);
+}
+
 static void (*skipTest)(skiatest::Reporter* , const char* filename) = 0;
-static void (*firstTest)(skiatest::Reporter* , const char* filename) = loops63i;
+static void (*firstTest)(skiatest::Reporter* , const char* filename) = 0;
 static void (*stopTest)(skiatest::Reporter* , const char* filename) = 0;
 
 #define TEST(name) { name, #name }
 
 static struct TestDesc tests[] = {
+    TEST(fuzz38),
     TEST(cubics44d),
     TEST(cubics45u),
     TEST(loops61i),