Introduce support for text-decoration-skip: ink

third_party/WebKit/Source/core/paint/TextPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/TextPainter.h"
 
 #include "core/CSSPropertyNames.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutObject.h"
 #include "core/layout/LayoutTextCombine.h"
@@ skipping 235 matching lines @@
     textRunPaintInfo.cachedTextBlob = cachedTextBlob;
     paintInternalRun<Step>(textRunPaintInfo, startOffset, endOffset);
   } else {
     if (endOffset > 0)
       paintInternalRun<Step>(textRunPaintInfo, 0, endOffset);
     if (startOffset < truncationPoint)
       paintInternalRun<Step>(textRunPaintInfo, startOffset, truncationPoint);
   }
 }
 
+void TextPainter::clipDecorationsStripe(float upper,
+                                        float stripeWidth,
+                                        float dilation) {
+  TextRunPaintInfo textRunPaintInfo(m_run);
+
+  if (!m_run.length())
+    return;
+
+  Vector<Font::TextIntercept> textIntercepts;
+  m_font.getTextIntercepts(
+      textRunPaintInfo, m_graphicsContext.deviceScaleFactor(),
+      m_graphicsContext.fillPaint(),
+      std::make_tuple(upper, upper + stripeWidth), textIntercepts);
+
+  for (auto intercept : textIntercepts) {
+    FloatPoint clipOrigin(m_textOrigin);
+    FloatRect clipRect(
+        clipOrigin + FloatPoint(intercept.m_begin, upper),
+        FloatSize(intercept.m_end - intercept.m_begin, stripeWidth));
+    clipRect.inflateX(dilation);
+    // We need to ensure the clip rectangle is covering the full underline
+    // extent. For horizontal drawing, using enclosingIntRect would be
+    // sufficient, since we can clamp to full device pixels that way. However,
+    // for vertical drawing, we have a transformation applied, which breaks the
+    // integers-equal-device pixels assumption, so vertically inflating by 1
+    // pixel makes sure we're always covering. This should only be done on the
+    // clipping rectangle, not when computing the glyph intersects.
+    clipRect.inflateY(1.0);
+    m_graphicsContext.clipOut(clipRect);
+  }
+}
+
 void TextPainter::paintEmphasisMarkForCombinedText() {
   const SimpleFontData* fontData = m_font.primaryFont();
   DCHECK(fontData);
   if (!fontData)
     return;
 
   DCHECK(m_combinedText);
   TextRun placeholderTextRun(&ideographicFullStopCharacter, 1);
   FloatPoint emphasisMarkTextOrigin(m_textBounds.x().toFloat(),
                                     m_textBounds.y().toFloat() +
                                         fontData->getFontMetrics().ascent() +
                                         m_emphasisMarkOffset);
   TextRunPaintInfo textRunPaintInfo(placeholderTextRun);
   textRunPaintInfo.bounds = FloatRect(m_textBounds);
   m_graphicsContext.concatCTM(rotation(m_textBounds, Clockwise));
   m_graphicsContext.drawEmphasisMarks(m_combinedText->originalFont(),
                                       textRunPaintInfo, m_emphasisMark,
                                       emphasisMarkTextOrigin);
   m_graphicsContext.concatCTM(rotation(m_textBounds, Counterclockwise));
 }
 
 }  // namespace blink