[Webkit-unassigned] [Bug 164949] -webkit-overflow-scrolling: touch completely breaks 3D perspective functionality

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=164949

--- Comment #4 from Frédéric Wang (:fredw) <fred.wang at free.fr> ---
Some preliminary debugging: When webkit-overflow-scrolling is absent RenderLayerCompositor::computeCompositingRequirements will execute

    if (!willBeComposited && canBeComposited(layer)
        && requiresCompositingForIndirectReason(layer.renderer(), childState.subtreeIsCompositing, anyDescendantHas3DTransform, indirectCompositingReason)) {
        layer.setIndirectCompositingReason(indirectCompositingReason);
        childState.compositingAncestor = &layer;
        overlapMap.pushCompositingContainer();
        addToOverlapMapRecursive(overlapMap, layer);
        willBeComposited = true;
    }

where requiresCompositingForIndirectReason returns true because of the perspective property on the overflow node and the 3D transform on its descendants. If the overflow node has overflow-scrolling:touch, willBeComposited is however set to true at the top of the function so this conditional is never executed. I'm not yet sure how/whether this is causing the bug, though.

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