Right now in layers-free webrender mode, APZ doesn't get any hit-testing information. In the long term we want to do hit-testing in WebRender but I think in the short term it makes sense to stand up some hit-testing in C++ code, reusing the existing APZ codepaths. It's not a lot of work (I have some patches already) but it will likely have poor performance. Still, it will allow us to turn on APZ sooner, which means we can run APZ-enabled reftests sooner, which I think will help development overall and avoid regressions when working on the more complete hit-test solution.

With these patches applied (and with everything else that's landed) APZ mostly works in layers-free mode. I'm sure there's a lot of edge cases and whatnot that aren't hooked up properly but basic scrolling seems ok.

Comment on attachment 8898878 [details] Bug 1389143 - Send event regions items over to APZ in layers-free mode. https://reviewboard.mozilla.org/r/170238/#review175436 ::: gfx/layers/LayersTypes.h:166 (Diff revision 1) > + { > + mHitRegion.OrWith(aOther.mHitRegion); > + mDispatchToContentHitRegion.OrWith(aOther.mDispatchToContentHitRegion); > + // See the comment in nsDisplayList::AddFrame, where the touch action regions > + // are handled. The same thing applies here. > + bool alreadyHadRegions = !mNoActionRegion.IsEmpty() || Sadly this logic is duplicated in a number of places but because it operates on slightly different inputs/data structures it's hard to refactor/reuse. See http://searchfox.org/mozilla-central/search?q=alreadyHadRegions for other places this pattern exists.

Comment on attachment 8898876 [details] Bug 1389143 - Refactor to extract helper method. https://reviewboard.mozilla.org/r/170234/#review175454

Comment on attachment 8898877 [details] Bug 1389143 - Preserve the lastASR tracker across recursions. https://reviewboard.mozilla.org/r/170236/#review175456

Comment on attachment 8898878 [details] Bug 1389143 - Send event regions items over to APZ in layers-free mode. https://reviewboard.mozilla.org/r/170238/#review175466

Comment on attachment 8898879 [details] Bug 1389143 - Send event regions override information to APZ in layers-free mode. https://reviewboard.mozilla.org/r/170240/#review175468

Pushed by kgupta@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/52917ec218cb Refactor to extract helper method. r=jrmuizel https://hg.mozilla.org/integration/autoland/rev/a8b2d799b3c0 Preserve the lastASR tracker across recursions. r=jrmuizel https://hg.mozilla.org/integration/autoland/rev/81116c9af1b1 Send event regions items over to APZ in layers-free mode. r=jrmuizel https://hg.mozilla.org/integration/autoland/rev/46a3b3a3ae70 Send event regions override information to APZ in layers-free mode. r=jrmuizel

https://hg.mozilla.org/mozilla-central/rev/52917ec218cb https://hg.mozilla.org/mozilla-central/rev/a8b2d799b3c0 https://hg.mozilla.org/mozilla-central/rev/81116c9af1b1 https://hg.mozilla.org/mozilla-central/rev/46a3b3a3ae70