Track the region where text is painted.

Source/core/platform/graphics/Font.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Holger Hans Peter Freyther
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 36 matching lines @@
 class FloatRect;
 class FontData;
 class FontMetrics;
 class FontPlatformData;
 class FontSelector;
 class GlyphBuffer;
 class GraphicsContext;
 class RenderText;
 class TextLayout;
 class TextRun;
+struct TextRunPaintInfo;
 
 struct GlyphData;
 
 struct GlyphOverflow {
     GlyphOverflow()
         : left(0)
         , right(0)
         , top(0)
         , bottom(0)
         , computeBounds(false)
@@ skipping 23 matching lines @@
     bool operator!=(const Font& other) const { return !(*this == other); }
 
     const FontDescription& fontDescription() const { return m_fontDescription; }
 
     int pixelSize() const { return fontDescription().computedPixelSize(); }
     float size() const { return fontDescription().computedSize(); }
 
     void update(PassRefPtr<FontSelector>) const;
 
     enum CustomFontNotReadyAction { DoNotPaintIfFontNotReady, UseFallbackIfFontNotReady };
-    void drawText(GraphicsContext*, const TextRun&, const FloatPoint&, int from = 0, int to = -1, CustomFontNotReadyAction = DoNotPaintIfFontNotReady) const;
-    void drawEmphasisMarks(GraphicsContext*, const TextRun&, const AtomicString& mark, const FloatPoint&, int from = 0, int to = -1) const;
+    void drawText(GraphicsContext*, const TextRunPaintInfo&, const FloatPoint&, CustomFontNotReadyAction = DoNotPaintIfFontNotReady) const;
+    void drawEmphasisMarks(GraphicsContext*, const TextRunPaintInfo&, const AtomicString& mark, const FloatPoint&) const;
 
     float width(const TextRun&, HashSet<const SimpleFontData*>* fallbackFonts = 0, GlyphOverflow* = 0) const;
     float width(const TextRun&, int& charsConsumed, String& glyphName) const;
 
     PassOwnPtr<TextLayout> createLayout(RenderText*, float xPos, bool collapseWhiteSpace) const;
     static void deleteLayout(TextLayout*);
     static float width(TextLayout&, unsigned from, unsigned len, HashSet<const SimpleFontData*>* fallbackFonts = 0);
 
     int offsetForPosition(const TextRun&, float position, bool includePartialGlyphs) const;
     FloatRect selectionRectForText(const TextRun&, const FloatPoint&, int h, int from = 0, int to = -1) const;
@@ skipping 54 matching lines @@
     enum CodePath { Auto, Simple, Complex, SimpleWithGlyphOverflow };
     CodePath codePath(const TextRun&) const;
     static CodePath characterRangeCodePath(const LChar*, unsigned) { return Simple; }
     static CodePath characterRangeCodePath(const UChar*, unsigned len);
     
 private:
     enum ForTextEmphasisOrNot { NotForTextEmphasis, ForTextEmphasis };
 
     // Returns the initial in-stream advance.
     float getGlyphsAndAdvancesForSimpleText(const TextRun&, int from, int to, GlyphBuffer&, ForTextEmphasisOrNot = NotForTextEmphasis) const;
-    void drawSimpleText(GraphicsContext*, const TextRun&, const FloatPoint&, int from, int to) const;
-    void drawEmphasisMarksForSimpleText(GraphicsContext*, const TextRun&, const AtomicString& mark, const FloatPoint&, int from, int to) const;
-    void drawGlyphs(GraphicsContext*, const SimpleFontData*, const GlyphBuffer&, int from, int to, const FloatPoint&) const;
-    void drawGlyphBuffer(GraphicsContext*, const TextRun&, const GlyphBuffer&, const FloatPoint&) const;
-    void drawEmphasisMarks(GraphicsContext*, const TextRun&, const GlyphBuffer&, const AtomicString&, const FloatPoint&) const;
+    void drawSimpleText(GraphicsContext*, const TextRunPaintInfo&, const FloatPoint&) const;
+    void drawEmphasisMarksForSimpleText(GraphicsContext*, const TextRunPaintInfo&, const AtomicString& mark, const FloatPoint&) const;
+    void drawGlyphs(GraphicsContext*, const SimpleFontData*, const GlyphBuffer&, int from, int to, const FloatPoint&, const FloatRect& textRect) const;

[bungeman-chromium, 2013/05/06 19:30:43]

Any reason why this is just a FloatRect?

[alokp, 2013/05/06 20:39:54]

I do not understand. If you mean why drawGlyphs does not use TextRunPaintInfo,
it is because the parameters for this function refers to the GlyphBuffer and not
TextRun.

[bungeman-chromium, 2013/05/06 21:02:31]

Hmmm... I see. The use case I had in mind meant passing this sort of information
potentially all the way down to Skia. This would allow the knowledge of glyph =>
character mappings to be pushed all the way down to the drawText call so that
PDF/XPS could save the mapping. Just passing a FloatRect here somewhat defeats
the purpose of the suggestion. Perhaps such a use case needs to be plumbed in
some other way (potentially somehow adding such information to the GlyphBuffer
directly).

On the other hand perhaps this isn't an impossible issue as this is just the
simple text path, the complex text path does get the full info.

[alokp, 2013/05/06 22:12:34]

Yes. Extra information could either be added directly to GlyphBuffer or to a
GlyphBuffer wrapper. The textRect parameter could then be moved to GlyphBuffer
wrapper.
 

+    void drawGlyphBuffer(GraphicsContext*, const TextRunPaintInfo&, const GlyphBuffer&, const FloatPoint&) const;
+    void drawEmphasisMarks(GraphicsContext*, const TextRunPaintInfo&, const GlyphBuffer&, const AtomicString&, const FloatPoint&) const;
     float floatWidthForSimpleText(const TextRun&, HashSet<const SimpleFontData*>* fallbackFonts = 0, GlyphOverflow* = 0) const;
     int offsetForPositionForSimpleText(const TextRun&, float position, bool includePartialGlyphs) const;
     FloatRect selectionRectForSimpleText(const TextRun&, const FloatPoint&, int h, int from, int to) const;
 
     bool getEmphasisMarkGlyphData(const AtomicString&, GlyphData&) const;
 
     static bool canReturnFallbackFontsForComplexText();
     static bool canExpandAroundIdeographsInComplexText();
 
     // Returns the initial in-stream advance.
     float getGlyphsAndAdvancesForComplexText(const TextRun&, int from, int to, GlyphBuffer&, ForTextEmphasisOrNot = NotForTextEmphasis) const;
-    void drawComplexText(GraphicsContext*, const TextRun&, const FloatPoint&, int from, int to) const;
-    void drawEmphasisMarksForComplexText(GraphicsContext*, const TextRun&, const AtomicString& mark, const FloatPoint&, int from, int to) const;
+    void drawComplexText(GraphicsContext*, const TextRunPaintInfo&, const FloatPoint&) const;
+    void drawEmphasisMarksForComplexText(GraphicsContext*, const TextRunPaintInfo&, const AtomicString& mark, const FloatPoint&) const;
     float floatWidthForComplexText(const TextRun&, HashSet<const SimpleFontData*>* fallbackFonts = 0, GlyphOverflow* = 0) const;
     int offsetForPositionForComplexText(const TextRun&, float position, bool includePartialGlyphs) const;
     FloatRect selectionRectForComplexText(const TextRun&, const FloatPoint&, int h, int from, int to) const;
 
     friend struct WidthIterator;
     friend class SVGTextRunRenderingContext;
 
 public:
     // Useful for debugging the different font rendering code paths.
     static void setCodePath(CodePath);
@@ skipping 128 matching lines @@
 
 }
 
 namespace WTF {
 
 template <> void deleteOwnedPtr<WebCore::TextLayout>(WebCore::TextLayout*);
 
 }
 
 #endif