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<body><span class="vcard"><a class="email" href="mailto:simon.fraser@apple.com" title="Simon Fraser (smfr) <simon.fraser@apple.com>"> <span class="fn">Simon Fraser (smfr)</span></a>
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<a class="bz_bug_link
bz_status_NEW "
title="NEW - Compositing layer is too large when inner element has a blur that is within bounds"
href="https://bugs.webkit.org/show_bug.cgi?id=155288">bug 155288</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Depends on</td>
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<td>81239
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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - Compositing layer is too large when inner element has a blur that is within bounds"
href="https://bugs.webkit.org/show_bug.cgi?id=155288#c1">Comment # 1</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - Compositing layer is too large when inner element has a blur that is within bounds"
href="https://bugs.webkit.org/show_bug.cgi?id=155288">bug 155288</a>
from <span class="vcard"><a class="email" href="mailto:simon.fraser@apple.com" title="Simon Fraser (smfr) <simon.fraser@apple.com>"> <span class="fn">Simon Fraser (smfr)</span></a>
</span></b>
<pre>For the first square:
renderer().style().filterOutsets().expandRect(unionBounds);
is adding 28px on each side for the 10px blur. This comes from outsetSizeForBlur() which has this comment:
// We take the half kernel size and multiply it with three, because we run box blur three times.
The kernel size is 19x19, which is computed by:
unsigned size = std::max<unsigned>(2, static_cast<unsigned>(floorf(value * gaussianKernelFactor() + 0.5f)));
where gaussianKernelFactor() returns 1.87997127
This is emulating the suggested approximation the SVG spec <<a href="https://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement">https://www.w3.org/TR/SVG/filters.html#feGaussianBlurElement</a>></pre>
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