Bug 1840075 - Implement support for the OpenType BASE (baselines) table, and use it to back canvas2d TextMetrics attributes and textBaseline alignment. r=gfx-reviewers,lsalzman

Differential Revision: https://phabricator.services.mozilla.com/D181882

dom/canvas/CanvasRenderingContext2D.cpp

@@ -4317,14 +4317,6 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
     const nsAString& aRawText, float aX, float aY,
     const Optional<double>& aMaxWidth, TextDrawOperation aOp,
     ErrorResult& aError) {
-  // Approximated baselines. In an ideal world, we'd read the baseline info
-  // directly from the font (where available). Alas we currently lack
-  // that functionality. These numbers are best guesses and should
-  // suffice for now. Both are fractions of the em ascent/descent from the
-  // alphabetic baseline.
-  const double kHangingBaselineDefault = 0.8;      // fraction of ascent
-  const double kIdeographicBaselineDefault = 0.5;  // fraction of descent
-
   gfxFontGroup* currentFontStyle = GetCurrentFontStyle();
   if (NS_WARN_IF(!currentFontStyle)) {
     aError = NS_ERROR_FAILURE;
@@ -4514,12 +4506,20 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
   float offsetX = anchorX * totalWidth;
   processor.mPt.x -= offsetX;
 
+  gfx::ShapedTextFlags runOrientation =
+      (processor.mTextRunFlags & gfx::ShapedTextFlags::TEXT_ORIENT_MASK);
+  nsFontMetrics::FontOrientation fontOrientation =
+      (runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_MIXED ||
+       runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_UPRIGHT)
+          ? nsFontMetrics::eVertical
+          : nsFontMetrics::eHorizontal;
+
   // offset pt.y (or pt.x, for vertical text) based on text baseline
   gfxFloat baselineAnchor;
 
   switch (state.textBaseline) {
     case CanvasTextBaseline::Hanging:
-      baselineAnchor = fontMetrics.emAscent * kHangingBaselineDefault;
+      baselineAnchor = font->GetBaselines(fontOrientation).mHanging;
       break;
     case CanvasTextBaseline::Top:
       baselineAnchor = fontMetrics.emAscent;
@@ -4528,10 +4528,10 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
       baselineAnchor = (fontMetrics.emAscent - fontMetrics.emDescent) * .5f;
       break;
     case CanvasTextBaseline::Alphabetic:
-      baselineAnchor = 0;
+      baselineAnchor = font->GetBaselines(fontOrientation).mAlphabetic;
       break;
     case CanvasTextBaseline::Ideographic:
-      baselineAnchor = -fontMetrics.emDescent * kIdeographicBaselineDefault;
+      baselineAnchor = font->GetBaselines(fontOrientation).mIdeographic;
       break;
     case CanvasTextBaseline::Bottom:
       baselineAnchor = -fontMetrics.emDescent;
@@ -4542,11 +4542,8 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
 
   // We can't query the textRun directly, as it may not have been created yet;
   // so instead we check the flags that will be used to initialize it.
-  gfx::ShapedTextFlags runOrientation =
-      (processor.mTextRunFlags & gfx::ShapedTextFlags::TEXT_ORIENT_MASK);
   if (runOrientation != gfx::ShapedTextFlags::TEXT_ORIENT_HORIZONTAL) {
-    if (runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_MIXED ||
+    if (fontOrientation == nsFontMetrics::eVertical) {
-        runOrientation == gfx::ShapedTextFlags::TEXT_ORIENT_VERTICAL_UPRIGHT) {
       // Adjust to account for mTextRun being shaped using center baseline
       // rather than alphabetic.
       baselineAnchor -= (fontMetrics.emAscent - fontMetrics.emDescent) * .5f;
@@ -4567,10 +4564,7 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
         -processor.mBoundingBox.Y() - baselineAnchor;
     double actualBoundingBoxDescent =
         processor.mBoundingBox.YMost() + baselineAnchor;
-    double hangingBaseline =
+    auto baselines = font->GetBaselines(fontOrientation);
-        fontMetrics.emAscent * kHangingBaselineDefault - baselineAnchor;
-    double ideographicBaseline =
-        -fontMetrics.emDescent * kIdeographicBaselineDefault - baselineAnchor;
     return new TextMetrics(
         totalWidth, actualBoundingBoxLeft, actualBoundingBoxRight,
         fontMetrics.maxAscent - baselineAnchor,   // fontBBAscent
@@ -4578,9 +4572,9 @@ TextMetrics* CanvasRenderingContext2D::DrawOrMeasureText(
         actualBoundingBoxAscent, actualBoundingBoxDescent,
         fontMetrics.emAscent - baselineAnchor,    // emHeightAscent
         -fontMetrics.emDescent - baselineAnchor,  // emHeightDescent
-        hangingBaseline,
+        baselines.mHanging - baselineAnchor,
-        -baselineAnchor,  // alphabeticBaseline
+        baselines.mAlphabetic - baselineAnchor,
-        ideographicBaseline);
+        baselines.mIdeographic - baselineAnchor);
   }
 
   // If we did not actually calculate bounds, set up a simple bounding box

gfx/thebes/gfxFont.cpp

@@ -4201,6 +4201,71 @@ void gfxFont::SanitizeMetrics(gfxFont::Metrics* aMetrics,
   }
 }
 
+gfxFont::Baselines gfxFont::GetBaselines(Orientation aOrientation) {
+  // Approximated baselines for fonts lacking actual baseline data. These are
+  // fractions of the em ascent/descent from the alphabetic baseline.
+  const double kHangingBaselineDefault = 0.8;       // fraction of ascent
+  const double kIdeographicBaselineDefault = -0.5;  // fraction of descent
+
+  // If no BASE table is present, just return synthetic values immediately.
+  if (!mFontEntry->HasFontTable(TRUETYPE_TAG('B', 'A', 'S', 'E'))) {
+    // No baseline table; just synthesize them immediately.
+    const Metrics& metrics = GetMetrics(aOrientation);
+    return Baselines{
+        0.0,                                             // alphabetic
+        kHangingBaselineDefault * metrics.emAscent,      // hanging
+        kIdeographicBaselineDefault * metrics.emDescent  // ideographic
+    };
+  }
+
+  // Use harfbuzz to try to read the font's baseline metrics.
+  Baselines result{NAN, NAN, NAN};
+  hb_font_t* hbFont = gfxHarfBuzzShaper::CreateHBFont(this);
+  hb_direction_t hbDir = aOrientation == nsFontMetrics::eHorizontal
+                             ? HB_DIRECTION_LTR
+                             : HB_DIRECTION_TTB;
+  hb_position_t position;
+  unsigned count = 0;
+  auto Fix2Float = [](hb_position_t f) -> gfxFloat { return f / 65536.0; };
+  if (hb_ot_layout_get_baseline(hbFont, HB_OT_LAYOUT_BASELINE_TAG_ROMAN, hbDir,
+                                HB_OT_TAG_DEFAULT_SCRIPT,
+                                HB_OT_TAG_DEFAULT_LANGUAGE, &position)) {
+    result.mAlphabetic = Fix2Float(position);
+    count++;
+  }
+  if (hb_ot_layout_get_baseline(hbFont, HB_OT_LAYOUT_BASELINE_TAG_HANGING,
+                                hbDir, HB_OT_TAG_DEFAULT_SCRIPT,
+                                HB_OT_TAG_DEFAULT_LANGUAGE, &position)) {
+    result.mHanging = Fix2Float(position);
+    count++;
+  }
+  if (hb_ot_layout_get_baseline(
+          hbFont, HB_OT_LAYOUT_BASELINE_TAG_IDEO_EMBOX_BOTTOM_OR_LEFT, hbDir,
+          HB_OT_TAG_DEFAULT_SCRIPT, HB_OT_TAG_DEFAULT_LANGUAGE, &position)) {
+    result.mIdeographic = Fix2Float(position);
+    count++;
+  }
+  hb_font_destroy(hbFont);
+  // If we successfully read all three, we can return now.
+  if (count == 3) {
+    return result;
+  }
+
+  // Synthesize the baselines that we didn't find in the font.
+  const Metrics& metrics = GetMetrics(aOrientation);
+  if (isnan(result.mAlphabetic)) {
+    result.mAlphabetic = 0.0;
+  }
+  if (isnan(result.mHanging)) {
+    result.mHanging = kHangingBaselineDefault * metrics.emAscent;
+  }
+  if (isnan(result.mIdeographic)) {
+    result.mIdeographic = kIdeographicBaselineDefault * metrics.emDescent;
+  }
+
+  return result;
+}
+
 // Create a Metrics record to be used for vertical layout. This should never
 // fail, as we've already decided this is a valid font. We do not have the
 // option of marking it invalid (as can happen if we're unable to read

gfx/thebes/gfxFont.h

@@ -1624,6 +1624,13 @@ class gfxFont {
     return *mVerticalMetrics;
   }
 
+  struct Baselines {
+    gfxFloat mAlphabetic;
+    gfxFloat mHanging;
+    gfxFloat mIdeographic;
+  };
+  Baselines GetBaselines(Orientation aOrientation);
+
   /**
    * We let layout specify spacing on either side of any
    * character. We need to specify both before and after

gfx/thebes/gfxOTSUtils.h

@@ -134,6 +134,10 @@ class MOZ_STACK_CLASS gfxOTSContext : public ots::OTSContext {
     if (aTag == TRUETYPE_TAG('S', 'V', 'G', ' ')) {
       return mKeepSVG ? ots::TABLE_ACTION_PASSTHRU : ots::TABLE_ACTION_DROP;
     }
+    // Preserve BASE table; harfbuzz will sanitize it before using.
+    if (aTag == TRUETYPE_TAG('B', 'A', 'S', 'E')) {
+      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;

modules/libpref/init/StaticPrefList.yaml

@@ -4200,7 +4200,7 @@
 
 - name: dom.textMetrics.baselines.enabled
   type: RelaxedAtomicBool
-  value: false
+  value: true
   mirror: always
 
 - name: dom.textMetrics.emHeight.enabled

testing/web-platform/meta/html/canvas/element/drawing-text-to-the-canvas/2d.text.measure.baselines.html.ini

@@ -1,5 +0,0 @@
-[2d.text.measure.baselines.html]
-  expected:
-    if (os == "android") and fission: [TIMEOUT, OK]
-  [Testing baselines]
-    expected: FAIL

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.baseline.default.html.ini

@@ -1,3 +0,0 @@
-[2d.text.baseline.default.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.baseline.invalid.html.ini

@@ -1,3 +0,0 @@
-[2d.text.baseline.invalid.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.baseline.valid.html.ini

@@ -1,3 +0,0 @@
-[2d.text.baseline.valid.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.alphabetic.html.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.alphabetic.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.bottom.html.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.bottom.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.hanging.html.ini

@@ -1,5 +0,0 @@
-[2d.text.draw.baseline.hanging.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Canvas test: 2d.text.draw.baseline.hanging]
-    expected: FAIL

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.ideographic.html.ini

@@ -1,5 +0,0 @@
-[2d.text.draw.baseline.ideographic.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]
-  [Canvas test: 2d.text.draw.baseline.ideographic]
-    expected: FAIL

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.middle.html.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.middle.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/text-styles/2d.text.draw.baseline.top.html.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.top.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/element/the-canvas-state/2d.state.saverestore.textBaseline.html.ini

@@ -1,3 +0,0 @@
-[2d.state.saverestore.textBaseline.html]
-  expected:
-    if (os == "android") and fission: [OK, TIMEOUT]

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.draw.baseline.hanging.html.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.hanging.html]
-  [OffscreenCanvas test: 2d.text.draw.baseline.hanging]
-    expected: FAIL

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.draw.baseline.hanging.worker.js.ini

@@ -1,3 +0,0 @@
-[2d.text.draw.baseline.hanging.worker.html]
-  [2d]
-    expected: FAIL

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.draw.baseline.ideographic.html.ini

@@ -1,5 +0,0 @@
-[2d.text.draw.baseline.ideographic.html]
-  expected:
-    if (os == "android") and fission: TIMEOUT
-  [OffscreenCanvas test: 2d.text.draw.baseline.ideographic]
-    expected: FAIL

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.draw.baseline.ideographic.worker.js.ini

@@ -1,4 +0,0 @@
-[2d.text.draw.baseline.ideographic.worker.html]
-  [2d]
-    expected: FAIL
-

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.measure.baselines.html.ini

@@ -1,4 +0,0 @@
-[2d.text.measure.baselines.html]
-  [Testing baselines for OffscreenCanvas]
-    expected: FAIL
-

testing/web-platform/meta/html/canvas/offscreen/text/2d.text.measure.baselines.worker.js.ini

@@ -1,4 +0,0 @@
-[2d.text.measure.baselines.worker.html]
-  [Testing baselines for OffscreenCanvas]
-    expected: FAIL
-

testing/web-platform/meta/html/dom/idlharness.https.html.ini

@@ -33,9 +33,6 @@ prefs: [dom.security.featurePolicy.experimental.enabled:true, dom.security.featu
   [CanvasRenderingContext2D interface: document.createElement("canvas").getContext("2d") must inherit property "getContextAttributes()" with the proper type]
     expected: FAIL
 
-  [TextMetrics interface: attribute ideographicBaseline]
-    expected: FAIL
-
   [VideoTrackList interface object length]
     expected: FAIL
 
@@ -186,9 +183,6 @@ prefs: [dom.security.featurePolicy.experimental.enabled:true, dom.security.featu
   [AudioTrack interface: attribute kind]
     expected: FAIL
 
-  [TextMetrics interface: attribute hangingBaseline]
-    expected: FAIL
-
   [VideoTrackList interface: existence and properties of interface prototype object]
     expected: FAIL
 
@@ -201,9 +195,6 @@ prefs: [dom.security.featurePolicy.experimental.enabled:true, dom.security.featu
   [VideoTrackList interface: existence and properties of interface prototype object's @@unscopables property]
     expected: FAIL
 
-  [TextMetrics interface: attribute alphabeticBaseline]
-    expected: FAIL
-
   [VideoTrackList interface: attribute length]
     expected: FAIL
 

testing/web-platform/meta/html/dom/idlharness.worker.js.ini

@@ -2,21 +2,12 @@
   [TextMetrics interface: attribute emHeightAscent]
     expected: FAIL
 
-  [TextMetrics interface: attribute ideographicBaseline]
-    expected: FAIL
-
   [OffscreenCanvasRenderingContext2D interface: attribute imageSmoothingQuality]
     expected: FAIL
 
   [TextMetrics interface: attribute emHeightDescent]
     expected: FAIL
 
-  [TextMetrics interface: attribute hangingBaseline]
-    expected: FAIL
-
-  [TextMetrics interface: attribute alphabeticBaseline]
-    expected: FAIL
-
   [ImageData interface: attribute colorSpace]
     expected: FAIL