[Webkit-unassigned] [Bug 181757] [WPE][GTK] Content disappearing when using CSS transforms

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=181757

--- Comment #7 from Miguel Gomez <magomez at igalia.com> ---
I found the cause of the problem. It happens when animating a layer that has a backingStore and an animation that causes the visible rect of the backingStore to change.

In a normal case, a layer is animated by the compositing thread, recalculating its transformation matrix as needed in its TextureMapperLayer, and no layer flushes are required for this.

But when using a backingStore whose visible rect can change due to the animation, we need to perform a layer flush because that's what recalculates the visible rect and creates the needed tiles in the backingStore. As we are not doing so, once the animation advances and the visible rect goes out of the initially created tiles nothing gets rendered inside the layer.

When the random number in the page changes, that causes a layer flush and updates the tiles in the animated layer, that's why it becomes visible at that point. Eventually the visible rect moves out of the current tiles again and the content disappears again.

We need to force a layer flush in the case of animations where the visible rect changes and require creating new tiles.

I'm lacking time to prepare a fix for this now, but I'll keep working on it as soon as I have time.

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