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chromium / chromium / src / 79ddf9920ca3221b5a6c8f5bca3252a5b0bec769 / . / third_party / WebKit / Source / platform / fonts
tree: 93956f6b8bdc94b7bf3f37275e247db3f9b79e73 [path history] [tgz]
  1. android/
  2. linux/
  3. mac/
  4. opentype/
  5. shaping/
  6. skia/
  7. win/
  8. AcceptLanguagesResolver.cpp
  9. AcceptLanguagesResolver.h
  10. AcceptLanguagesResolverTest.cpp
  11. AlternateFontFamily.h
  12. CharacterRange.h
  13. CustomFontData.h
  14. FallbackListCompositeKey.h
  15. Font.cpp
  16. Font.h
  17. FontBaseline.h
  18. FontCache.cpp
  19. FontCache.h
  20. FontCacheClient.h
  21. FontCacheKey.h
  22. FontCacheMemoryDumpProvider.cpp
  23. FontCacheMemoryDumpProvider.h
  24. FontCacheTest.cpp
  25. FontCustomPlatformData.cpp
  26. FontCustomPlatformData.h
  27. FontData.cpp
  28. FontData.h
  29. FontDataCache.cpp
  30. FontDataCache.h
  31. FontDataForRangeSet.cpp
  32. FontDataForRangeSet.h
  33. FontDescription.cpp
  34. FontDescription.h
  35. FontDescriptionTest.cpp
  36. FontFaceCreationParams.h
  37. FontFallbackIterator.cpp
  38. FontFallbackIterator.h
  39. FontFallbackList.cpp
  40. FontFallbackList.h
  41. FontFallbackPriority.cpp
  42. FontFallbackPriority.h
  43. FontFamily.cpp
  44. FontFamily.h
  45. FontFamilyNames.json5
  46. FontMetrics.h
  47. FontOrientation.h
  48. FontPlatformData.cpp
  49. FontPlatformData.h
  50. FontPlatformDataTest.cpp
  51. FontSelector.h
  52. FontSmoothingMode.h
  53. FontTest.cpp
  54. FontTraits.h
  55. FontVariantNumeric.h
  56. FontWidthVariant.h
  57. GenericFontFamilySettings.cpp
  58. GenericFontFamilySettings.h
  59. GenericFontFamilySettingsTest.cpp
  60. Glyph.h
  61. GlyphMetricsMap.h
  62. LocaleInFonts.md
  63. OrientationIterator.cpp
  64. OrientationIterator.h
  65. OrientationIteratorTest.cpp
  66. README.md
  67. ScriptRunIterator.cpp
  68. ScriptRunIterator.h
  69. ScriptRunIteratorTest.cpp
  70. SegmentedFontData.cpp
  71. SegmentedFontData.h
  72. SimpleFontData.cpp
  73. SimpleFontData.h
  74. SmallCapsIterator.cpp
  75. SmallCapsIterator.h
  76. SmallCapsIteratorTest.cpp
  77. SymbolsIterator.cpp
  78. SymbolsIterator.h
  79. SymbolsIteratorTest.cpp
  80. TextRenderingMode.h
  81. TypesettingFeatures.h
  82. UnicodeRangeSet.cpp
  83. UnicodeRangeSet.h
  84. UnicodeRangeSetTest.cpp
  85. UTF16TextIterator.cpp
  86. UTF16TextIterator.h
  87. VDMXParser.cpp
  88. VDMXParser.h
  89. WebFontDecoder.cpp
  90. WebFontDecoder.h
third_party/WebKit/Source/platform/fonts/README.md

Blink's Text Stack

This README serves as an documentation entry point of Blink's text stack.

This README can be viewed in formatted form here.

Overview

Blink's text stack covers those functional parts of the layout engine that process CSS-styled HTML text. From source document to visual output this rougly comprises the following stages:

Mapping CSS Style to Font Objects

TODO(drott): Describe steps from ComputedStyle, FontBuilder to FontDescription and Font objects.

Font Matching

TODO(drott): Describe font matching against system fonts in platform specific implementations as well as matching against web fonts in FontStyleMatcher.

Word Cache

TODO(drott,eae): Describe at which level the word cache hooks in, how the cache keys are calculated and its approach of word and CJK segmentation.

Run Segmentation

TODO(drott): Describe purpose and run segmentation approach of RunSegmenter.

Text Shaping

The low level shaping implementation is in shaping/HarfBuzzShaper.h and shaping/HarfBuzzShaper.cpp

Shaping text runs is split into several stages: Run segmentation, shaping the initial segment, identify shaped and non-shaped sequences of the shaping result, and processing sub-runs by trying to shape them with a fallback font until the last resort font is reached.

If caps formatting is requested, an additional lowercase/uppercase segmentation stage is required. In this stage, OpenType features in the font are matched against the requested formatting and formatting is synthesized as required by the CSS Level 3 Fonts Module.

Below we will go through one example - for simplicity without caps formatting - to illustrate the process: The following is a run of vertical text to be shaped. After run segmentation in RunSegmenter it is split into 4 segments. The segments indicated by the segementation results showing the script, orientation information and small caps handling of the individual segment. The Japanese text at the beginning has script “Hiragana”, does not need rotation when laid out vertically and does not need uppercasing when small caps is requested.

0 い
1 ろ
2 は USCRIPT_HIRAGANA,
    OrientationIterator::OrientationKeep,
    SmallCapsIterator::SmallCapsSameCase

3 a
4 ̄ (Combining Macron)
5 a
6 A USCRIPT_LATIN,
    OrientationIterator::OrientationRotateSideways,
    SmallCapsIterator::SmallCapsUppercaseNeeded

7 い
8 ろ
9 は USCRIPT_HIRAGANA,
     OrientationIterator::OrientationKeep,
     SmallCapsIterator::SmallCapsSameCase

Let's assume the CSS for this text run is as follows: font-family: "Heiti SC", Tinos, sans-serif; where Tinos is a web font, defined as a composite font, with two sub ranges, one for Latin U+00-U+FF and one unrestricted unicode-range.

FontFallbackIterator provides the shaper with Heiti SC, then Tinos of the restricted unicode-range, then the unrestricted full unicode-range Tinos, then a system sans-serif.

The initial segment 0-2 to the shaper, together with the segmentation properties and the initial Heiti SC font. Characters 0-2 are shaped successfully with Heiti SC. The next segment, 3-5 is passed to the shaper. The shaper attempts to shape it with Heiti SC, which fails for the Combining Macron. So the shaping result for this segment would look similar to this.

Glyphpos: 0 1 2 3
Cluster:  0 0 2 3
Glyph:    a x a A (where x is .notdef)

Now in the extractShapeResults() step we notice that there is more work to do, since Heiti SC does not have a glyph for the Combining Macron combined with an a. So, this cluster together with a Todo item for switching to the next font is put into HolesQueue.

After shaping the initial segment, the remaining items in the HolesQueue are processed, picking them from the head of the queue. So, first, the next font is requested from the FontFallbackIterator. In this case, Tinos (for the range U+00-U+FF) comes back. Shaping using this font, assuming it is subsetted, fails again since there is no combining mark available. This triggers requesting yet another font. This time, the Tinos font for the full range. With this, shaping succeeds with the following HarfBuzz result:

Glyphpos 0 1 2 3
Cluster: 0 0 2 3
Glyph:   a ◌̄ a A (with glyph coordinates placing the ◌̄ above the first a)

Now this sub run is successfully processed and can be appended to ShapeResult. A new ShapeResult::RunInfo is created. The logic in ShapeResult::insertRun then takes care of merging the shape result into the right position the vector of RunInfos in ShapeResult.

Shaping then continues analogously for the remaining Hiragana Japanese sub-run, and the result is inserted into ShapeResult as well.

Font Fallback

TODO(drott): Describe when font fallback is invoked, and how FontFallbackIterator cycles through fallback fonts during shaping.