Remove troublesome DCHECK() in homogenousLimitNearZero.

This DCHECK() has become more trouble than it's worth, given that there are enough edge cases that can cause it to fail in various ways. So just turn it into a code comment. Fixed: 1230937 Bug: 1224066 Change-Id: Ia66eb51771b993c760e84f204c1f2e006b633441 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3046409 Commit-Queue: David Baron <dbaron@chromium.org> Commit-Queue: Robert Flack <flackr@chromium.org> Auto-Submit: David Baron <dbaron@chromium.org> Reviewed-by: Robert Flack <flackr@chromium.org> Cr-Commit-Position: refs/heads/master@{#904586}
Denger-Network · Jul 23, 2021 · feae95a · feae95a
1 parent 0a41f34
commit feae95a
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Showing 2 changed files with 26 additions and 3 deletions.
diff --git a/cc/base/math_util.cc b/cc/base/math_util.cc
@@ -133,9 +133,11 @@ static void homogenousLimitNearZero(SkScalar a1,
   if (std::abs(a1 * w2 / w1 / a2 - 1.0f) > kStationaryPointEpsilon) {
     // t has been computed so that w is near but not at zero.
     *limit = ((1.0f - t) * a1 + t * a2) / ((1.0f - t) * w1 + t * w2);
-    DCHECK(t == 0.0f || t == 1.0f ||
-           std::abs(*limit) * 0.998f <
-               HomogeneousCoordinate::kInfiniteCoordinate);
+    // std::abs(*limit) should now be somewhere near
+    // HomogeneousCoordinate::kInfiniteCoordinate, preferably smaller than it,
+    // but there are edge cases where it will be larger (for example, if the
+    // point where a crosses 0 is very close to the point where w crosses 0),
+    // so it's hard to DCHECK() that this is the case.
   } else {
     *limit = a1 / w1;  // (== a2 / w2) && == (1.0f - t) * a1 / w1 + t * a2 / w2
   }

diff --git a/...party/blink/web_tests/external/wpt/css/css-transforms/crashtests/w-crossing-zero-001.html b/...party/blink/web_tests/external/wpt/css/css-transforms/crashtests/w-crossing-zero-001.html
@@ -0,0 +1,21 @@
+<!DOCTYPE HTML>
+<title>CSS Test (Transforms): Transform with w crossing zero</title>
+<link rel="author" title="L. David Baron" href="https://dbaron.org/">
+<link rel="author" title="Google" href="http://www.google.com/">
+<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1230937">
+<link rel="help" href="https://drafts.csswg.org/css-transforms-2/#processing-of-perspective-transformed-boxes">
+<meta name="assert" content="This should not crash.">
+
+<style>
+#outer {
+  transform-style: preserve-3d;
+}
+#inner {
+  transform: matrix3d(4,947066.75,3,-57.374,1860.6956175,97,2291.191,-8.1785,9,46.047,5.02880,7.198084,2,8,2009,3.2);
+  border: medium solid;
+}
+</style>
+<div id="outer">
+  <div id="inner">
+  </div>
+</div>