Bug 1765093 - patch 3 - Also use the new gfxTextRun::GetLineHeightMetrics to optimize GetAscentAndDescentInAppUnits. r=emilio

This accelerates web-exposed SVG APIs such as getExtentOfChar() by avoiding the expensive
MeasureText() call when we're just getting the line-height metrics.

Differential Revision: https://phabricator.services.mozilla.com/D145717

gfx/thebes/gfxTextRun.cpp

@@ -845,10 +845,10 @@ gfxTextRun::Metrics gfxTextRun::MeasureText(
   return accumulatedMetrics;
 }
 
-void gfxTextRun::GetLineHeightMetrics(gfxFloat& aAscent,
+void gfxTextRun::GetLineHeightMetrics(Range aRange, gfxFloat& aAscent,
                                       gfxFloat& aDescent) const {
   Metrics accumulatedMetrics;
-  GlyphRunIterator iter(this, Range(this));
+  GlyphRunIterator iter(this, aRange);
   while (iter.NextRun()) {
     gfxFont* font = iter.GetGlyphRun()->mFont;
     auto metrics =

gfx/thebes/gfxTextRun.h

@@ -312,7 +312,11 @@ class gfxTextRun : public gfxShapedText {
                        aDrawTargetForTightBoundingBox, aProvider);
   }
 
-  void GetLineHeightMetrics(gfxFloat& aAscent, gfxFloat& aDescent) const;
+  void GetLineHeightMetrics(Range aRange, gfxFloat& aAscent,
+                            gfxFloat& aDescent) const;
+  void GetLineHeightMetrics(gfxFloat& aAscent, gfxFloat& aDescent) const {
+    GetLineHeightMetrics(Range(this), aAscent, aDescent);
+  }
 
   /**
    * Computes just the advance width for a substring.

layout/svg/SVGTextFrame.cpp

@@ -126,13 +126,7 @@ static void GetAscentAndDescentInAppUnits(nsTextFrame* aFrame,
   gfxTextRun::Range range = ConvertOriginalToSkipped(
       it, aFrame->GetContentOffset(), aFrame->GetContentLength());
 
-  // We pass in null for the PropertyProvider since letter-spacing and
-  // word-spacing should not affect the ascent and descent values we get.
-  gfxTextRun::Metrics metrics =
-      textRun->MeasureText(range, gfxFont::LOOSE_INK_EXTENTS, nullptr, nullptr);
-
-  aAscent = metrics.mAscent;
-  aDescent = metrics.mDescent;
+  textRun->GetLineHeightMetrics(range, aAscent, aDescent);
 }
 
 /**