Bug 1796648 - Drop any SVG table from downloaded fonts if OpenType-SVG rendering is disabled. r=gfx-reviewers,lsalzman

This makes e.g. https://nabla.typearture.com/ perform VASTLY better on macOS if OT-SVG is preffed off;
without it, we get bogged down in Core Text internally parsing all the SVG when all we want are the
TrueType outlines.

Differential Revision: https://phabricator.services.mozilla.com/D159888

gfx/thebes/gfxOTSUtils.h

@@ -102,23 +102,18 @@ class MOZ_STACK_CLASS gfxOTSContext : public ots::OTSContext {
     // Whether to preserve color bitmap glyphs
     mKeepColorBitmaps =
         StaticPrefs::gfx_downloadable_fonts_keep_color_bitmaps();
+    // Whether to preserve SVG glyphs (which can be expensive in Core Text,
+    // so better to drop them if we're not going to render them anyhow).
+    mKeepSVG = StaticPrefs::gfx_font_rendering_opentype_svg_enabled();
   }
 
   virtual ots::TableAction GetTableAction(uint32_t aTag) override {
-    // Preserve Graphite and SVG tables,
-    // and possibly OTL and Variation tables (depending on prefs)
+    // Pass through or validate OTL and Variation tables, depending on prefs.
     if ((!mCheckOTLTables && (aTag == TRUETYPE_TAG('G', 'D', 'E', 'F') ||
                               aTag == TRUETYPE_TAG('G', 'P', 'O', 'S') ||
                               aTag == TRUETYPE_TAG('G', 'S', 'U', 'B')))) {
       return ots::TABLE_ACTION_PASSTHRU;
     }
-    if (aTag == TRUETYPE_TAG('S', 'V', 'G', ' ')) {
-      return ots::TABLE_ACTION_PASSTHRU;
-    }
-    if (mKeepColorBitmaps && (aTag == TRUETYPE_TAG('C', 'B', 'D', 'T') ||
-                              aTag == TRUETYPE_TAG('C', 'B', 'L', 'C'))) {
-      return ots::TABLE_ACTION_PASSTHRU;
-    }
     auto isVariationTable = [](uint32_t aTag) -> bool {
       return aTag == TRUETYPE_TAG('a', 'v', 'a', 'r') ||
              aTag == TRUETYPE_TAG('c', 'v', 'a', 'r') ||
@@ -135,6 +130,14 @@ class MOZ_STACK_CLASS gfxOTSContext : public ots::OTSContext {
     if (!gfxPlatform::HasVariationFontSupport() && isVariationTable(aTag)) {
       return ots::TABLE_ACTION_DROP;
     }
+    // Preserve SVG table if OpenType-SVG rendering is enabled.
+    if (aTag == TRUETYPE_TAG('S', 'V', 'G', ' ')) {
+      return mKeepSVG ? ots::TABLE_ACTION_PASSTHRU : ots::TABLE_ACTION_DROP;
+    }
+    if (mKeepColorBitmaps && (aTag == TRUETYPE_TAG('C', 'B', 'D', 'T') ||
+                              aTag == TRUETYPE_TAG('C', 'B', 'L', 'C'))) {
+      return ots::TABLE_ACTION_PASSTHRU;
+    }
     return ots::TABLE_ACTION_DEFAULT;
   }
 
@@ -169,6 +172,7 @@ class MOZ_STACK_CLASS gfxOTSContext : public ots::OTSContext {
   bool mCheckOTLTables;
   bool mCheckVariationTables;
   bool mKeepColorBitmaps;
+  bool mKeepSVG;
 };
 
 #endif /* GFX_OTS_UTILS_H */

layout/reftests/text-svgglyphs/reftest.list

@@ -1,9 +1,9 @@
 defaults pref(gfx.font_rendering.opentype_svg.enabled,true)
 
-pref(gfx.font_rendering.opentype_svg.enabled,false) != svg-glyph-basic.svg svg-glyph-basic-ref.svg
+pref(gfx.font_rendering.opentype_svg.enabled,false) != svg-glyph-basic-disabled.svg svg-glyph-basic-ref.svg
 fuzzy(0-1,0-200) == svg-glyph-basic.svg svg-glyph-basic-ref.svg
 == svg-glyph-invalid-ids.svg svg-glyph-invalid-ids-ref.svg
-pref(gfx.font_rendering.opentype_svg.enabled,false) != svg-glyph-positioning.svg svg-glyph-positioning-ref.svg
+pref(gfx.font_rendering.opentype_svg.enabled,false) != svg-glyph-positioning-disabled.svg svg-glyph-positioning-ref.svg
 fuzzy(0-2,0-350) == svg-glyph-positioning.svg svg-glyph-positioning-ref.svg
 == svg-glyph-html.html svg-glyph-html-ref.svg
 == svg-glyph-direct.svg svg-glyph-direct-ref.svg

layout/reftests/text-svgglyphs/svg-glyph-basic-disabled.svg

@@ -0,0 +1,27 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <style type="text/css">
+    <![CDATA[
+      @font-face {
+        font-family: "Liberation";
+        /* For testing with the pref disabled, add a query to the font URL
+           to avoid cache confusion between enabled/disabled. */
+        src:url(resources/svg.woff?disabled);
+      }
+      text
+      {
+        font-family: Liberation;
+        font-size: 200px;
+        stroke: black;
+      }
+    ]]>
+  </style>
+  <!--
+      Test that SVG glyphs are being drawn instead of TrueType glyphs
+      Also testing that this does not happen if the
+      gfx.font_rendering.opentype_svg.enabled preference is set to true.
+  -->
+  <!-- glyphid -->
+  <text x="0" y="200">
+  L
+  </text>
+</svg>

layout/reftests/text-svgglyphs/svg-glyph-positioning-disabled.svg

@@ -0,0 +1,25 @@
+<svg xmlns="http://www.w3.org/2000/svg">
+  <style type="text/css">
+    <![CDATA[
+      @font-face {
+        font-family: "Liberation";
+        /* For testing with the pref disabled, add a query to the font URL
+           to avoid cache confusion between enabled/disabled. */
+        src:url(resources/svg.woff?disabled);
+      }
+      text
+      {
+        font-family: Liberation;
+        font-size: 200px;
+        stroke: black;
+      }
+    ]]>
+  </style>
+  <!--
+      Test that we're rendering in the right place in the middle of a
+      text run
+  -->
+  <text x="0" y="200">
+  LLL
+  </text>
+</svg>