Use visual runs and save ShapeResults in TextMetrics #46833
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A previous CL implemented `TextMetrics::getSelectionRects()` by saving the logical runs produced by `BidiParagraph`. This approach can fail when the direction of text in the canvas is set directly with `ctx.direction`, as the visual order of the runs (and therefore the correct selection rects) can change without modifying the order in which the logical runs are processed. This change uses `BidiParagraph::GetVisualRuns()` instead, to iterate the runs in the visual order. To calculate selection rects from these runs, it is necessary to save the starting x position and character offset in the input string. Additionally, in order to avoid shaping the text over and over again, the `ShapeResult` cache is only generated the first time the new method is called. A new struct was created to hold the information needed for each run. We defer the actual shaping of its `ShapeResult` as to not significantly affect the performance of `ctx.measureText()`. Bug: 341213359 Change-Id: Iba4c461cddafa3d00d309f9a48e848b75ca84ff6
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A previous CL implemented
TextMetrics::getSelectionRects()by savingthe logical runs produced by
BidiParagraph. This approach can failwhen the direction of text in the canvas is set directly with
ctx.direction, as the visual order of the runs (and therefore thecorrect selection rects) can change without modifying the order in which
the logical runs are processed.
This change uses
BidiParagraph::GetVisualRuns()instead, to iterate theruns in the visual order. To calculate selection rects from these runs,
it is necessary to save the starting x position and character offset in
the input string.
Additionally, in order to avoid shaping the text over and over again,
the
ShapeResultcache is only generated the first time the new methodis called. A new struct was created to hold the information needed for
each run. We defer the actual shaping of its
ShapeResultas to notsignificantly affect the performance of
ctx.measureText().Bug: 341213359
Change-Id: Iba4c461cddafa3d00d309f9a48e848b75ca84ff6
Reviewed-on: https://chromium-review.googlesource.com/5593278
WPT-Export-Revision: 0a3e301c2c0cff2d7c47916821618ed3ce428e3a