Fix some shadow issues.

* Clamp path polygon points to nearest 1/16th of a pixel to help
  with floating point issues.
* Added check for multiple contour paths.
* Return empty SkVertices for certain degenerate cases to avoid
  unnecessary blurs.
* Check iteration count in SkOffsetPolygon to avoid infinite loops.
* Add new tests to verify these.

Bug: skia:
Change-Id: Ie6ad48d2504e065dcc822609d369f90c56ef3ad3
Reviewed-on: https://skia-review.googlesource.com/136701
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

1 files changed, 75 insertions, 21 deletions

diff --git a/tests/ShadowTest.cpp b/tests/ShadowTest.cpp
index 90c1d8ffcc..07ff6dfdce 100644
--- a/tests/ShadowTest.cpp
+++ b/tests/ShadowTest.cpp
@@ -13,31 +13,40 @@
 #include "SkVertices.h"
 #include "Test.h"
 
-void tessellate_shadow(skiatest::Reporter* reporter, const SkPath& path, const SkMatrix& ctm,
-                       bool expectSuccess) {
-
-    auto heightParams = SkPoint3::Make(0, 0, 4);
+enum ExpectVerts {
+    kDont_ExpectVerts,
+    kDo_ExpectVerts
+};
 
-    auto verts = SkShadowTessellator::MakeAmbient(path, ctm, heightParams, true);
+void check_result(skiatest::Reporter* reporter, sk_sp<SkVertices> verts,
+                  ExpectVerts expectVerts, bool expectSuccess) {
     if (expectSuccess != SkToBool(verts)) {
         ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
                expectSuccess ? "succeed" : "fail");
     }
-    verts = SkShadowTessellator::MakeAmbient(path, ctm, heightParams, false);
-    if (expectSuccess != SkToBool(verts)) {
-        ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
-               expectSuccess ? "succeed" : "fail");
+    if (SkToBool(verts)) {
+        if (kDont_ExpectVerts == expectVerts && verts->vertexCount()) {
+            ERRORF(reporter, "Expected shadow tessellation to generate no vertices but it did.");
+        } else if (kDo_ExpectVerts == expectVerts && !verts->vertexCount()) {
+            ERRORF(reporter, "Expected shadow tessellation to generate vertices but it didn't.");
+        }
     }
+}
+
+void tessellate_shadow(skiatest::Reporter* reporter, const SkPath& path, const SkMatrix& ctm,
+                       const SkPoint3& heightParams, ExpectVerts expectVerts, bool expectSuccess) {
+
+    auto verts = SkShadowTessellator::MakeAmbient(path, ctm, heightParams, true);
+    check_result(reporter, verts, expectVerts, expectSuccess);
+
+    verts = SkShadowTessellator::MakeAmbient(path, ctm, heightParams, false);
+    check_result(reporter, verts, expectVerts, expectSuccess);
+
     verts = SkShadowTessellator::MakeSpot(path, ctm, heightParams, {0, 0, 128}, 128.f, false);
-    if (expectSuccess != SkToBool(verts)) {
-        ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
-               expectSuccess ? "succeed" : "fail");
-    }
+    check_result(reporter, verts, expectVerts, expectSuccess);
+
     verts = SkShadowTessellator::MakeSpot(path, ctm, heightParams, {0, 0, 128}, 128.f, false);
-    if (expectSuccess != SkToBool(verts)) {
-        ERRORF(reporter, "Expected shadow tessellation to %s but it did not.",
-               expectSuccess ? "succeed" : "fail");
-    }
+    check_result(reporter, verts, expectVerts, expectSuccess);
 }
 
 DEF_TEST(ShadowUtils, reporter) {
@@ -45,19 +54,64 @@ DEF_TEST(ShadowUtils, reporter) {
 
     SkPath path;
     path.cubicTo(100, 50, 20, 100, 0, 0);
-    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), true);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 4}, kDo_ExpectVerts, true);
+    // super high path
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 4.0e+37f},
+                      kDo_ExpectVerts, true);
 
     // This line segment has no area and no shadow.
     path.reset();
     path.lineTo(10.f, 10.f);
-    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), false);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 4}, kDont_ExpectVerts, true);
 
-    // A series of colinear line segments
+    // A series of collinear line segments
     path.reset();
     for (int i = 0; i < 10; ++i) {
         path.lineTo((SkScalar)i, (SkScalar)i);
     }
-    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), false);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 4}, kDont_ExpectVerts, true);
+
+    // ugly degenerate path
+    path.reset();
+    path.moveTo(-134217728, 2.22265153e+21f);
+    path.cubicTo(-2.33326106e+21f, 7.36298265e-41f, 3.72237738e-22f, 5.99502692e-36f,
+                 1.13631943e+22f, 2.0890786e+33f);
+    path.cubicTo(1.03397626e-25f, 5.99502692e-36f, 9.18354962e-41f, 0, 4.6142745e-37f, -213558848);
+    path.lineTo(-134217728, 2.2226515e+21f);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 9}, kDont_ExpectVerts, true);
+
+    // simple concave path (star of David)
+    path.reset();
+    path.moveTo(0.0f, -50.0f);
+    path.lineTo(14.43f, -25.0f);
+    path.lineTo(43.30f, -25.0f);
+    path.lineTo(28.86f, 0.0f);
+    path.lineTo(43.30f, 25.0f);
+    path.lineTo(14.43f, 25.0f);
+    path.lineTo(0.0f, 50.0f);
+    path.lineTo(-14.43f, 25.0f);
+    path.lineTo(-43.30f, 25.0f);
+    path.lineTo(-28.86f, 0.0f);
+    path.lineTo(-43.30f, -25.0f);
+    path.lineTo(-14.43f, -25.0f);
+// uncomment when transparent concave shadows are working
+//    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 9}, kDo_ExpectVerts, true);
+
+    // complex concave path (bowtie)
+    path.reset();
+    path.moveTo(-50, -50);
+    path.lineTo(-50, 50);
+    path.lineTo(50, -50);
+    path.lineTo(50, 50);
+    path.lineTo(-50, -50);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 9}, kDont_ExpectVerts, false);
+
+    // multiple contour path
+    path.close();
+    path.moveTo(0, 0);
+    path.lineTo(1, 0);
+    path.lineTo(0, 1);
+    tessellate_shadow(reporter, path, canvas.getTotalMatrix(), {0, 0, 9}, kDont_ExpectVerts, false);
 }
 
 void check_xformed_bounds(skiatest::Reporter* reporter, const SkPath& path, const SkMatrix& ctm) {