50417 2010-12-02 15:54:51 -0800 Avoid repainting compositing layers unnecessarily when layout changes 2017-08-17 13:12:07 -0700 1 1 1 Unclassified WebKit Layout and Rendering 528+ (Nightly build) PC OS X 10.5 NEW InRadar P2 Normal --- 74370 1 simon.fraser simon.fraser dino ed_dvd igor.oliveira jchaffraix simon.fraser webkit-bug-importer zalan oldest_to_newest 316479 0 simon.fraser 2010-12-02 15:54:51 -0800 RenderBoxModelObject::styleWillChange() has this code: if (diff == StyleDifferenceLayout) { // When a layout hint happens, we go ahead and do a repaint of the layer, since the layer could // end up being destroyed. if (hasLayer()) { if (style()->position() != newStyle->position() || style()->zIndex() != newStyle->zIndex() || style()->hasAutoZIndex() != newStyle->hasAutoZIndex() || !(style()->clip() == newStyle->clip()) || style()->hasClip() != newStyle->hasClip() || style()->opacity() != newStyle->opacity() || style()->transform() != newStyle->transform()) layer()->repaintIncludingDescendants(); This can cause extra repainting of compositing layers when they don't need to be repainted. 334070 1 simon.fraser 2011-01-13 18:15:33 -0800 <rdar://problem/8863549> 335990 2 simon.fraser 2011-01-18 12:21:54 -0800 There's also this: inline void RenderObject::setNeedsLayout(bool b, bool markParents) { bool alreadyNeededLayout = m_needsLayout; m_needsLayout = b; if (b) { ASSERT(!isSetNeedsLayoutForbidden()); if (!alreadyNeededLayout) { ... if (hasLayer()) setLayerNeedsFullRepaint(); 1339710 3 simon.fraser 2017-08-17 13:11:54 -0700 One specific example we should optimize is to avoid repaints when doing a "positioned movement only" layout.