This is a well-known issue. Ideally outline size would be factored into visual overflow, but that’s a bit tricky because outline is weird and crosses between RenderObjects.
https://bugs.webkit.org/show_bug.cgi?id=106397 <https://bugs.webkit.org/show_bug.cgi?id=106397> > On Jul 6, 2015, at 9:26 PM, Kim, NamHoon <na...@ea.com> wrote: > > Hi experts, > > While hacking composited layer in WebKit, I realized CSS outline style > inflate size of all RenderLayers. Since WebKit has default css of 5px outline > for focused element, focusing input in the below sample inflate the cyan box. > This can reproduced in WK2 OSX port in r186227. > > <style> > .box { > position: fixed; > top: 50px; > width: 100px; > height: 30px; > border-radius: 10%; > background-color: cyan; > } > </style> > > <input type='text'> > <div class='box'></div> > > Through investigation, I found `RenderView::m_maximalOutlineSize` value is > set in the RenderElement::setStyle() function. And this cause inflation of > layers in RenderLayer::localBoundingBox() function. Since setter of > `m_maximalOutlineSize` scheduled rebuild of the whole composited layers, all > layers inflated by the value. > > Honestly, I don’t know about this value’s purpose. But it seems weird to me > that this value does not cleared in the RenderView even after outline style > cleared. (i.e. loose focus of the input) > > And this behavior makes several problem in our ports, [EAWebKit][1]. Since we > uses composited layers backed by DirectX, this makes paint call requests > larger size than texture itself in TextureMapperTile::paint() function. This > cause rendering of corrupted memory. Steps follow, > > a. layer inflated by maximalOutlineSize. Let 100x100 layer increased to > 110x110. > b. texture increased in the > TextureMapperTiledBackingStore::createOrDestroyTilesIfNeeded() to 110x110. > c. layer’s texture destroyed then reconstructed by display style change. > d. while reconstruct of the layer’s texture, this time texture created with > the size of 100x100 instead of 110x110. > e. then painting this texture in TextureMapperTile::paint() request 110x110 > rect for 100x100 texture. This sounds like a bug in your port. > While step d. GraphicsLayerTextureMapper::m_needsDisplayRect intersected with > TextureMapperTile::m_rect, makes texture smaller then layer’s size. On the > other hand, TextureMapperTile::paint() call in the step e. request whole > TextureMapperTile::m_rect for draw request. > > To escape this problem, I overridden default style of :focus to `outline: > none`. I wonder better solution for this. Is it some bug of WebKit? Is there > some proper way to handle this? If inflation of the layers inevitable, it > seems reasonable shrunken back after outline style cleared. Simon
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