SVG: Increase hit-testing precision on strokes

Skia takes a precision value when generating strokes as an optimization. When rendering, we pass a value derived from the scale-factor in the CTM, but when hit-testing we were passing a hard-coded value. This worked reasonably well for solid strokes at moderate scales. However, at sufficiently high scales and especially for dashed strokes, the stroke generated for hit-testing was noticeably different from the rendered stroke. This change passes the CTM through to the hit-testing code, so that we can use the same high precision for hit testing as rendering. Bug: 964614 Change-Id: I8dfcb3ade86b9e7b63c7415baab5814ac2286ce8 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2112955 Reviewed-by: Ian Prest <iapres@microsoft.com> Reviewed-by: Philip Rogers <pdr@chromium.org> Reviewed-by: Fernando Serboncini <fserb@chromium.org> Reviewed-by: Fredrik Söderquist <fs@opera.com> Commit-Queue: Ian Prest <iapres@microsoft.com> Cr-Commit-Position: refs/heads/master@{#759761}
web-platform-tests · Apr 16, 2020 · 6ac09a5 · 6ac09a5
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diff --git a/2dcontext/path-objects/2d.path.isPointInStroke.scaleddashes.html b/2dcontext/path-objects/2d.path.isPointInStroke.scaleddashes.html
@@ -0,0 +1,40 @@
+<!DOCTYPE html>
+<!-- DO NOT EDIT! This test has been generated by /2dcontext/tools/gentest.py. -->
+<title>Canvas test: 2d.path.isPointInStroke.scaleddashes</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/2dcontext/resources/canvas-tests.js"></script>
+<link rel="stylesheet" href="/2dcontext/resources/canvas-tests.css">
+<body class="show_output">
+
+<h1>2d.path.isPointInStroke.scaleddashes</h1>
+<p class="desc">isPointInStroke() should return correct results on dashed paths at high scale factors</p>
+
+
+<p class="output">Actual output:</p>
+<canvas id="c" class="output" width="100" height="50"><p class="fallback">FAIL (fallback content)</p></canvas>
+
+<ul id="d"></ul>
+<script>
+var t = async_test("isPointInStroke() should return correct results on dashed paths at high scale factors");
+_addTest(function(canvas, ctx) {
+
+var scale = 20;
+ctx.setLineDash([10, 21.4159]); // dash from t=0 to t=10 along the circle
+ctx.scale(scale, scale);
+ctx.ellipse(6, 10, 5, 5, 0, 2*Math.PI, false);
+ctx.stroke();
+
+// hit-test the beginning of the dash (t=0)
+_assertSame(ctx.isPointInStroke(11*scale, 10*scale), true, "ctx.isPointInStroke(11*scale, 10*scale)", "true");
+// hit-test the middle of the dash (t=5)
+_assertSame(ctx.isPointInStroke(8.70*scale, 14.21*scale), true, "ctx.isPointInStroke(8.70*scale, 14.21*scale)", "true");
+// hit-test the end of the dash (t=9.8)
+_assertSame(ctx.isPointInStroke(4.10*scale, 14.63*scale), true, "ctx.isPointInStroke(4.10*scale, 14.63*scale)", "true");
+// hit-test past the end of the dash (t=10.2)
+_assertSame(ctx.isPointInStroke(3.74*scale, 14.46*scale), false, "ctx.isPointInStroke(3.74*scale, 14.46*scale)", "false");
+
+
+});
+</script>
+
diff --git a/2dcontext/tools/tests2d.yaml b/2dcontext/tools/tests2d.yaml
@@ -8646,6 +8646,27 @@
     @assert ctx.isPointInPath(NaN, NaN) === false;
 
 
+- name: 2d.path.isPointInStroke.scaleddashes
+  desc: isPointInStroke() should return correct results on dashed paths at high scale factors
+  testing:
+    - 2d.path.isPointInStroke
+  code: |
+    var scale = 20;
+    ctx.setLineDash([10, 21.4159]); // dash from t=0 to t=10 along the circle
+    ctx.scale(scale, scale);
+    ctx.ellipse(6, 10, 5, 5, 0, 2*Math.PI, false);
+    ctx.stroke();
+
+    // hit-test the beginning of the dash (t=0)
+    @assert ctx.isPointInStroke(11*scale, 10*scale) === true;
+    // hit-test the middle of the dash (t=5)
+    @assert ctx.isPointInStroke(8.70*scale, 14.21*scale) === true;
+    // hit-test the end of the dash (t=9.8)
+    @assert ctx.isPointInStroke(4.10*scale, 14.63*scale) === true;
+    // hit-test past the end of the dash (t=10.2)
+    @assert ctx.isPointInStroke(3.74*scale, 14.46*scale) === false;
+
+
 - name: 2d.drawImage.3arg
   testing:
     - 2d.drawImage.defaultsource

diff --git a/svg/shapes/scripted/stroke-dashes-hit-at-high-scale.svg b/svg/shapes/scripted/stroke-dashes-hit-at-high-scale.svg
diff --git a/svg/types/scripted/SVGGeometryElement.isPointInStroke-02.svg b/svg/types/scripted/SVGGeometryElement.isPointInStroke-02.svg