Improve line breaking performance for complex text
https://bugs.webkit.org/show_bug.cgi?id=83045
Patch by Ned Holbrook <nholbrook@apple.com> on 2012-08-27
Reviewed by Darin Adler.
Currently RenderBlock::LineBreaker::nextLineBreak assumes that measuring individual words is as cheap
as free. This is not the case when dealing with complex text, which benefits from laying out as much
text as possible and by reusing that layout when feasible: by doing so this patch improves line
breaking by 25% as measured with a simple test app.
The bulk of this change is modifying ComplexTextController::advance, which previously required the
text offset to be strictly increasing and assumed unidirectional text; now it supports random seeking
in a naive fashion (by restarting to the beginning) and traverses glyphs in logical order. In the
latter case, the presence of any non-LTR runs triggers the population of a mapping from logical to
visual run indices. Finally, a new flag has been added which inhibits glyph advances from being split
across ligatures (thus causing spurious line breaks).
A ComplexTextController and its associated TextRun and Font are encapsulated in a TextLayout object,
which is instantiated as an opaque object via functions that are no-ops unless building for Mac. A
static member function (isNeeded) checks to see whether a TextRun is complex, in order to avoid
needless instantiation. It also bails if tabs would be enabled since positional effects are not yet
handled in this mode.
No behavioral changes are expected due to this change, so no new tests.
* platform/graphics/Font.cpp:
(WTF): Define deleteOwnedPtr for TextLayout as calling through destroyLayout; relying on operator delete is not workable as the class does not exist on all platforms.
(WTF::WebCore::TextLayout):
(WebCore): Implement no-op TextLayout wrappers for non-Mac platforms.
(WebCore::Font::createLayout):
(WebCore::Font::deleteLayout):
(WebCore::Font::width):
* platform/graphics/Font.h:
(WebCore): Add forward declarations for RenderText and TextLayout.
(Font): Add functions for dealing with pointer to TextLayout implementation.
(WTF): Declare deleteOwnedPtr for TextLayout.
* platform/graphics/mac/ComplexTextController.cpp:
(TextLayout): An instance of this class corresponds to a ComplexTextController for a particular TextRun.
(WebCore::TextLayout::isNeeded): Used by wrapper to avoid instantiation when complex layout is not required.
(WebCore::TextLayout::TextLayout):
(WebCore::TextLayout::width):
(WebCore::TextLayout::fontWithNoWordSpacing): Helper function to allow initialization of member variable.
(WebCore::TextLayout::constructTextRun): Ditto.
(WebCore): Implement real TextLayout wrappers for Mac.
(WebCore::Font::createLayout):
(WebCore::Font::deleteLayout):
(WebCore::Font::width):
(WebCore::ComplexTextController::ComplexTextController): Initialize m_ltrOnly and reserve initial capacity for m_runIndices.
(WebCore::ComplexTextController::indexOfCurrentRun): Return (visual) m_complexTextRuns index corresponding to (logical) m_currentRun, lazily constructing m_runIndices if needed.
(WebCore::ComplexTextController::incrementCurrentRun): Return next m_complexTextRuns index in logical order.
(WebCore::ComplexTextController::advance): Allow restarting, support for bidi reordering, and option to measure only whole glyphs rather than dividing advances.
(WebCore::ComplexTextController::adjustGlyphsAndAdvances): Clear m_ltrOnly on detecting a RTL run.
* platform/graphics/mac/ComplexTextController.h:
(ComplexTextController): Add m_ltrOnly indicating no bidi reordering, and m_runIndices mapping from runs (logical order) to m_complexTextRuns (visual order).
(WebCore::ComplexTextController::ComplexTextRun::indexBegin):
(WebCore::ComplexTextController::ComplexTextRun::isLTR):
(ComplexTextRun): Add helper functions returning values pertinent to individual runs as opposed to the entire containing line.
(WebCore::ComplexTextController::stringBegin): Return first string index.
(WebCore::ComplexTextController::stringEnd): Return one past last string index.
* platform/graphics/mac/ComplexTextControllerCoreText.mm: Initialize m_indexBegin and m_ltr.
(WebCore::ComplexTextController::ComplexTextRun::ComplexTextRun): Initialize m_indexBegin and m_ltr.
* rendering/RenderBlock.h:
(RenderTextInfo): Add single mapping from RenderText to LazyLineBreakIterator and (possibly null) TextLayout since they are recreated under the same circumstances.
* rendering/RenderBlockLineLayout.cpp:
(WebCore::RenderBlock::RenderTextInfo::RenderTextInfo): Make non-inline to avoid compilation errors.
(WebCore::RenderBlock::RenderTextInfo::~RenderTextInfo): Ditto.
(WebCore::RenderBlock::layoutRunsAndFloatsInRange): Allow RenderTextInfo to be reused across calls to nextLineBreak.
(WebCore::textWidth): Use TextLayout when supplied for measuring.
(WebCore::RenderBlock::LineBreaker::nextLineBreak):
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@126763 268f45cc-cd09-0410-ab3c-d52691b4dbfc
8 files changed
