1866411 - sync decoding of images causes unnecessary invalidates that hide bugs and make it hard to write some tests

Status: NEW

(Testing :: Reftest, defect)

Description

[Timothy Nikkel (:tnikkel)]

Having sync decoding enabled can affect tests that don't even contain images because we will hit this code

https://searchfox.org/mozilla-central/rev/66d0e3cac02896d0249c6077742411722e6333f0/layout/painting/RetainedDisplayListBuilder.cpp#1572

that invalidates every display item that may contain an image.

This, for example, hides bug 1866410. It also makes it impossible to write a reftest/crashtest for bug 1862277. And it's not obvious that this is the cause so it takes developer time.

Comment 1

[Timothy Nikkel (:tnikkel)]

I think we can probably fix this by skipping the linked invalidation code if the sync decoding pref is set because that means every paint is one with sync decode and we only need that code if we are mixing sync and non-sync paints. (I think we can get away with not supporting the case of dynamically flipping the pref perfectly.)