keep SVG arcs axis aligned

Computing the arc width introduces rounding errors that cause the
arc to exceed 1/4 circle and cause integer anchored arcs to start
outside their marks. A round rect may lose convexity as a result.

Check if arcTo() inputs are integers and arc is 90 degrees;
if so, output conics which are axis-aligned on integers as well.

This is triggered when using SVG to represent a round rect.

Possible future enhancements are recorded in bug.skia.org/7383

R=reed@google.com,djsollen@google.com
Change-Id: I6609456fcefabcda6c9560a044533ecb5cda2d31
Reviewed-on: https://skia-review.googlesource.com/79423
Reviewed-by: Derek Sollenberger <djsollen@google.com>
Commit-Queue: Derek Sollenberger <djsollen@google.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/PathTest.cpp b/tests/PathTest.cpp
index b275342e2d..b36179000f 100644
--- a/tests/PathTest.cpp
+++ b/tests/PathTest.cpp
@@ -4915,3 +4915,31 @@ DEF_TEST(NonFinitePathIteration, reporter) {
 
     REPORTER_ASSERT(reporter, verbs == 0);
 }
+
+DEF_TEST(AndroidArc, reporter) {
+    const char* tests[] = {
+        "M50,0A50,50,0,0 1 100,50 L100,85 A15,15,0,0 1 85,100 L50,100 A50,50,0,0 1 50,0z",
+        "M50,0L92,0 A8,8,0,0 1 100,8 L100,92 A8,8,0,0 1 92,100 L8,100"
+            " A8,8,0,0 1 0,92 L 0,8 A8,8,0,0 1 8,0z",
+        "M50 0A50 50,0,1,1,50 100A50 50,0,1,1,50 0"
+    };
+    for (auto test : tests) {
+        SkPath aPath;
+        SkAssertResult(SkParsePath::FromSVGString(test, &aPath));
+        SkASSERT(aPath.isConvex());
+        for (SkScalar scale = 1; scale < 1000; scale *= 1.1f) {
+            SkPath scalePath = aPath;
+            SkMatrix matrix;
+            matrix.setScale(scale, scale);
+            scalePath.transform(matrix);
+            SkASSERT(scalePath.isConvex());
+        }
+        for (SkScalar scale = 1; scale < .001; scale /= 1.1f) {
+            SkPath scalePath = aPath;
+            SkMatrix matrix;
+            matrix.setScale(scale, scale);
+            scalePath.transform(matrix);
+            SkASSERT(scalePath.isConvex());
+        }
+    }
+}