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Bug 1356114 - Part 1: Change the code that optimizes away CSS border corner painting to ensure opposite sides have the same length. r=jwatt

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See https://bugzilla.mozilla.org/show_bug.cgi?id=1356114#c8
for a diagram describing the old behavior.
This commit is contained in:
Tooru Fujisawa 2017-08-06 00:26:57 +09:00
parent 75303aec29
commit a1b9a771f1
1 changed files with 58 additions and 11 deletions
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69
layout/painting/nsCSSRenderingBorders.cpp
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@ -3378,15 +3378,61 @@ nsCSSBorderRenderer::DrawBorders()
/* We have more than one pass to go. Draw the corners separately from the sides. */
/*
* If we have a 1px-wide border, the corners are going to be
* negligible, so don't bother doing anything fancy. Just extend
* the top and bottom borders to the right 1px and the left border
* to the bottom 1px. We do this by twiddling the corner dimensions,
* which causes the right to happen later on. Only do this if we have
* a 1.0 unit border all around and no border radius.
*/
// The corner is going to have negligible size if its two adjacent border
// sides are only 1px wide and there is no border radius. In that case we
// skip the overhead of painting the corner by setting the width or height
// of the corner to zero, which effectively extends one of the corner's
// adjacent border sides. We extend the longer adjacent side so that
// opposite sides will be the same length, which is necessary for opposite
// dashed/dotted sides to be symmetrical.
//
// if width > height
// +--+--------------+--+ +--------------------+
// | | | | | |
// +--+--------------+--+ +--+--------------+--+
// | | | | | | | |
// | | | | => | | | |
// | | | | | | | |
// +--+--------------+--+ +--+--------------+--+
// | | | | | |
// +--+--------------+--+ +--------------------+
//
// if width <= height
// +--+--------+--+ +--+--------+--+
// | | | | | | | |
// +--+--------+--+ | +--------+ |
// | | | | | | | |
// | | | | | | | |
// | | | | | | | |
// | | | | => | | | |
// | | | | | | | |
// | | | | | | | |
// | | | | | | | |
// +--+--------+--+ | +--------+ |
// | | | | | | | |
// +--+--------+--+ +--+--------+--+
//
// Note that if we have different border widths we could end up with
// opposite sides of different length. For example, if the left and
// bottom borders are 2px wide instead of 1px, we will end up doing
// something like:
//
// +----+------------+--+ +----+---------------+
// | | | | | | |
// +----+------------+--+ +----+------------+--+
// | | | | | | | |
// | | | | => | | | |
// | | | | | | | |
// +----+------------+--+ +----+------------+--+
// | | | | | | | |
// | | | | | | | |
// +----+------------+--+ +----+------------+--+
//
// XXX Should we only do this optimization if |allBordersSameWidth| is true?
//
// XXX In fact is this optimization even worth the complexity it adds to
// the code? 1px wide dashed borders are not overly common, and drawing
// corners for them is not that expensive.
NS_FOR_CSS_FULL_CORNERS(corner) {
const mozilla::Side sides[2] = { mozilla::Side(corner), PREV_SIDE(corner) };
@ -3394,10 +3440,11 @@ nsCSSBorderRenderer::DrawBorders()
continue;
if (mBorderWidths[sides[0]] == 1.0 && mBorderWidths[sides[1]] == 1.0) {
if (corner == eCornerTopLeft || corner == eCornerTopRight)
if (mOuterRect.Width() > mOuterRect.Height()) {
mBorderCornerDimensions[corner].width = 0.0;
else
} else {
mBorderCornerDimensions[corner].height = 0.0;
}
}
}