From 5f570eddfa914f30495661869d3edf404f6f811e Mon Sep 17 00:00:00 2001
From: Robert Longson <longsonr@gmail.com>
Date: Sat, 10 Jan 2015 22:17:57 +0000
Subject: [PATCH] Bug 1117514 - lines with zero length dashes are not rendered.
 r=jwatt

---
 dom/svg/SVGContentUtils.cpp                   | 20 +++++++++++++++----
 ...ke-linecap-round-w-zero-length-segs-01.svg |  8 ++++++++
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/dom/svg/SVGContentUtils.cpp b/dom/svg/SVGContentUtils.cpp
index dee47cb5befb..9fef9b3bb731 100644
--- a/dom/svg/SVGContentUtils.cpp
+++ b/dom/svg/SVGContentUtils.cpp
@@ -138,12 +138,24 @@ GetStrokeDashData(SVGContentUtils::AutoStrokeOptions* aStrokeOptions,
     totalLengthOfGaps += origTotalLengthOfDashes;
   }
 
-  if (totalLengthOfDashes <= 0 || totalLengthOfGaps <= 0) {
-    if (totalLengthOfGaps > 0 && totalLengthOfDashes <= 0) {
-      return eNoStroke;
-    }
+  // Stroking using dashes is much slower than stroking a continuous line
+  // (see bug 609361 comment 40), and much, much slower than not stroking the
+  // line at all. Here we check for cases when the dash pattern causes the
+  // stroke to essentially be continuous or to be nonexistent in which case
+  // we can avoid expensive stroking operations (the underlying platform
+  // graphics libraries don't seem to optimize for this).
+  if (totalLengthOfDashes <= 0 && totalLengthOfGaps <= 0) {
+    return eNoStroke;
+  }
+  if (totalLengthOfGaps <= 0) {
     return eContinuousStroke;
   }
+  // We can only return eNoStroke if the value of stroke-linecap isn't
+  // adding caps to zero length dashes.
+  if (totalLengthOfDashes <= 0 &&
+      aStyleSVG->mStrokeLinecap == NS_STYLE_STROKE_LINECAP_BUTT) {
+    return eNoStroke;
+  }
 
   if (aContextPaint && aStyleSVG->mStrokeDashoffsetFromObject) {
     aStrokeOptions->mDashOffset = Float(aContextPaint->GetStrokeDashOffset());
diff --git a/layout/reftests/svg/stroke-linecap-round-w-zero-length-segs-01.svg b/layout/reftests/svg/stroke-linecap-round-w-zero-length-segs-01.svg
index 19059b6ccfa4..475b536ef4d9 100644
--- a/layout/reftests/svg/stroke-linecap-round-w-zero-length-segs-01.svg
+++ b/layout/reftests/svg/stroke-linecap-round-w-zero-length-segs-01.svg
@@ -144,4 +144,12 @@ path.coverer {
     <path class="coverer" d="M20,20 L30,30 M70,70 L80,80"/>
   </g>
 
+  <!-- Column 5: test stroke-dasharray -->
+
+  <g transform="translate(525,25)">
+    <circle cy="0" r="8"/>
+    <circle cy="40" r="8"/>
+    <circle cy="80" r="8"/>
+    <path class="circles-expected" d="M0,0v81" stroke-dasharray="0 40" />
+  </g>
 </svg>