Font metrics, version 1

Source/core/html/canvas/CanvasRenderingContext2D.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2007 Alp Toker <alp@atoker.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008 Dirk Schulze <krit@webkit.org>
  * Copyright (C) 2010 Torch Mobile (Beijing) Co. Ltd. All rights reserved.
  * Copyright (C) 2012, 2013 Intel Corporation. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
@@ skipping 2142 matching lines @@
 void CanvasRenderingContext2D::strokeText(const String& text, float x, float y, float maxWidth)
 {
     drawTextInternal(text, x, y, false, maxWidth, true);
 }
 
 PassRefPtr<TextMetrics> CanvasRenderingContext2D::measureText(const String& text)
 {
     FontCachePurgePreventer fontCachePurgePreventer;
     RefPtr<TextMetrics> metrics = TextMetrics::create();
     canvas()->document().updateStyleIfNeeded();
-    metrics->setWidth(accessFont().width(TextRun(text)));
+    const Font& font = accessFont();
+    const TextRun textRun(text);
+    FloatRect textBounds = font.selectionRectForText(textRun, FloatPoint(), font.fontDescription().computedSize(), 0, -1, true);
+
+    // x direction
+    metrics->setWidth(font.width(textRun));
+    metrics->setActualBoundingBoxLeft(-textBounds.x());
+    metrics->setActualBoundingBoxRight(textBounds.maxX());
+
+    // y direction
+    const FontMetrics& fontMetrics = font.fontMetrics();
+    const float ascent = fontMetrics.floatAscent();
+    const float descent = fontMetrics.floatDescent();
+    const float baselineY = getFontBaseline(fontMetrics);
+
+    metrics->setFontBoundingBoxAscent(ascent - baselineY);
+    metrics->setFontBoundingBoxDescent(descent + baselineY);
+    metrics->setActualBoundingBoxAscent(-textBounds.y() - baselineY);
+    metrics->setActualBoundingBoxDescent(textBounds.maxY() + baselineY);
+
+    // Note : top/bottom and ascend/descend are currently the same, so there's no difference
+    //        between the EM box's top and bottom and the font's ascend and descend
+    metrics->setEmHeightAscent(0);
+    metrics->setEmHeightDescent(0);
+
+    metrics->setHangingBaseline(-0.8f * ascent + baselineY);
+    metrics->setAlphabeticBaseline(baselineY);
+    metrics->setIdeographicBaseline(descent + baselineY);
     return metrics.release();
 }
 
 static void replaceCharacterInString(String& text, WTF::CharacterMatchFunctionPtr matchFunction, const String& replacement)
 {
     const size_t replacementLength = replacement.length();
     size_t index = 0;
     while ((index = text.find(matchFunction, index)) != kNotFound) {
         text.replace(index, 1, replacement);
         index += replacementLength;
@@ skipping 36 matching lines @@
 
     // FIXME: Need to turn off font smoothing.
 
     RenderStyle* computedStyle = canvas()->computedStyle();
     TextDirection direction = computedStyle ? computedStyle->direction() : LTR;
     bool isRTL = direction == RTL;
     bool override = computedStyle ? isOverride(computedStyle->unicodeBidi()) : false;
 
     TextRun textRun(normalizedText, 0, 0, TextRun::AllowTrailingExpansion, direction, override, true, TextRun::NoRounding);
     // Draw the item text at the correct point.
-    FloatPoint location(x, y);
-    switch (state().m_textBaseline) {
-    case TopTextBaseline:
-    case HangingTextBaseline:
-        location.setY(y + fontMetrics.ascent());
-        break;
-    case BottomTextBaseline:
-    case IdeographicTextBaseline:
-        location.setY(y - fontMetrics.descent());
-        break;
-    case MiddleTextBaseline:
-        location.setY(y - fontMetrics.descent() + fontMetrics.height() / 2);
-        break;
-    case AlphabeticTextBaseline:
-    default:
-         // Do nothing.
-        break;
-    }
+    FloatPoint location(x, y + getFontBaseline(fontMetrics));
 
     float fontWidth = font.width(TextRun(normalizedText, 0, 0, TextRun::AllowTrailingExpansion, direction, override));
 
     useMaxWidth = (useMaxWidth && maxWidth < fontWidth);
     float width = useMaxWidth ? maxWidth : fontWidth;
 
     TextAlign align = state().m_textAlign;
     if (align == StartTextAlign)
         align = isRTL ? RightTextAlign : LeftTextAlign;
     else if (align == EndTextAlign)
@@ skipping 53 matching lines @@
 
 const Font& CanvasRenderingContext2D::accessFont()
 {
     // This needs style to be up to date, but can't assert so because drawTextInternal
     // can invalidate style before this is called (e.g. drawingContext invalidates style).
     if (!state().m_realizedFont)
         setFont(state().m_unparsedFont);
     return state().m_font;
 }
 
+int CanvasRenderingContext2D::getFontBaseline(const FontMetrics& fontMetrics) const
+{
+    switch (state().m_textBaseline) {
+    case TopTextBaseline:
+        return fontMetrics.ascent();
+    case HangingTextBaseline:
+        // According to http://wiki.apache.org/xmlgraphics-fop/LineLayout/AlignmentHandling
+        // "FOP (Formatting Objects Processor) puts the hanging baseline at 80% of the ascender height"
+        return (fontMetrics.ascent() * 4) / 5;

[sugoi1, 2014/01/31 21:56:05]

I modified the hanging baseline from "ascent" to "0.8 * ascent", in accordance
with the standard.

+    case BottomTextBaseline:
+    case IdeographicTextBaseline:
+        return -fontMetrics.descent();
+    case MiddleTextBaseline:
+        return -fontMetrics.descent() + fontMetrics.height() / 2;
+    case AlphabeticTextBaseline:
+    default:
+        // Do nothing.
+        break;
+    }
+    return 0;
+}
+
 blink::WebLayer* CanvasRenderingContext2D::platformLayer() const
 {
     return canvas()->buffer() ? canvas()->buffer()->platformLayer() : 0;
 }
 
 bool CanvasRenderingContext2D::imageSmoothingEnabled() const
 {
     return state().m_imageSmoothingEnabled;
 }
 
@@ skipping 106 matching lines @@
     const int focusRingWidth = 5;
     const int focusRingOutline = 0;
     c->drawFocusRing(path, focusRingWidth, focusRingOutline, focusRingColor);
 
     c->restore();
 
     didDraw(dirtyRect);
 }
 
 } // namespace WebCore