Bug 1603629 - fix dominant-baseline hanging and mathematical r=jfkthame

Differential Revision: https://phabricator.services.mozilla.com/D88877

layout/reftests/svg/reftest.list

@@ -485,6 +485,7 @@ random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-layout-05.svg text-
 fuzzy-if(cocoaWidget&&layersGPUAccelerated,0-1,0-3) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-layout-06.svg text-layout-06-ref.svg # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-layout-07.svg text-layout-07-ref.svg # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-layout-08.svg text-layout-08-ref.svg # Bug 1392106
+random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-layout-09.svg pass.svg # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-scale-01.svg text-scale-01-ref.svg # Bug 1392106
 fuzzy-if(skiaContent,0-2,0-1000) random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-scale-02.svg text-scale-02-ref.svg # Bug 1392106
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == text-scale-03.svg text-scale-03-ref.svg # Bug 1392106

layout/reftests/svg/text-layout-09.svg

@@ -0,0 +1,51 @@
+<svg width="100%" height="100%" xmlns="http://www.w3.org/2000/svg" class="reftest-wait">
+
+  <foreignObject><canvas xmlns="http://www.w3.org/1999/xhtml" id="canvas"/></foreignObject>
+
+  <rect width="100%" height="100%" fill="lime"/>
+
+  <g fill="red">
+    <text dominant-baseline="hanging" x="70" y="70">hanging</text>
+    <text dominant-baseline="mathematical" x="70" y="140">mathematical</text>
+  </g>
+
+  <g fill="lime">
+    <text id="hanging" x="70" y="70" dy="0">hanging</text>
+    <text id="mathematical" x="70" y="140" dy="0">mathematical</text>
+  </g>
+
+  <style><![CDATA[
+  text {
+    font: bold 30px Verdana, Helvetica, Arial, sans-serif;
+  }
+  ]]></style>
+  <script>
+  function cover(element) {
+    let rect = document.createElementNS("http://www.w3.org/2000/svg", "rect");
+    let bbox = element.getBBox(); 
+    rect.x.baseVal.value = bbox.x;
+    rect.y.baseVal.value = bbox.y;
+    rect.width.baseVal.value = bbox.width;
+    rect.height.baseVal.value = bbox.height;
+    element.parentElement.appendChild(rect);
+  }
+  onload = function() {
+    const canvas = document.getElementById('canvas');
+    const ctx = canvas.getContext('2d');
+    ctx.font = 'bold 30px Verdana, Helvetica, Arial, sans-serif';
+
+    let text = 'h';
+    let textMetrics = ctx.measureText(text);
+
+    let hanging = document.getElementById("hanging");
+    hanging.dy.baseVal[0].value = textMetrics.actualBoundingBoxAscent * 1.1;
+    cover(hanging);
+
+    let mathematical = document.getElementById("mathematical");
+    mathematical.dy.baseVal[0].value = textMetrics.actualBoundingBoxAscent / 2 * 1.4;
+    cover(mathematical);
+
+    document.documentElement.removeAttribute('class');
+  }
+  </script>
+</svg>

layout/svg/SVGTextFrame.cpp

@@ -286,6 +286,7 @@ static nscoord GetBaselinePosition(nsTextFrame* aFrame, gfxTextRun* aTextRun,
 
   switch (aDominantBaseline) {
     case StyleDominantBaseline::Hanging:
+      return metrics.mAscent * 0.2;
     case StyleDominantBaseline::TextBeforeEdge:
       return writingMode.IsVerticalRL() ? metrics.mAscent + metrics.mDescent
                                         : 0;
@@ -308,8 +309,9 @@ static nscoord GetBaselinePosition(nsTextFrame* aFrame, gfxTextRun* aTextRun,
                                         : metrics.mAscent + metrics.mDescent;
 
     case StyleDominantBaseline::Central:
-    case StyleDominantBaseline::Mathematical:
       return (metrics.mAscent + metrics.mDescent) / 2.0;
+    case StyleDominantBaseline::Mathematical:
+      return metrics.mAscent / 2.0;
   }
 
   MOZ_ASSERT_UNREACHABLE("unexpected dominant-baseline value");