Bugzilla

(In reply to Botond Ballo [:botond] from comment #18)
> One thing I do not yet understand is: if the resolution is 1.31 when the video is in fullscreen mode and we have reflowed the page into a 1280 CSS pixel ICB, why isn't the video visually zoomed in (such that its right and bottom parts, including the bottom bar, are offscreen)? That's what I would expect the rendering to be in this state (and if that _were_ the rendering, the underlying bug would be much more obvious from the get-go).

The reason for this is that we [skip building an async zoom container](https://searchfox.org/mozilla-central/rev/95935109bbbd4a39d612a917e59025f9c81f9d76/layout/painting/nsDisplayList.cpp#877) if the document is in fullscreen mode. This was also introduced in bug 1696717.

It's a bit of a footgun that there exists a set of conditions under which we ignore `PresShell::mResolution` for rendering purposes (by not building an async zoom container), but still use it for hit-testing purposes. We may want to consider at least detecting and asserting if that ever happens.

(In reply to Botond Ballo [:botond] from comment #18)
> One thing I do not yet understand is: if the resolution is 1.31 when the video is in fullscreen mode and we have reflowed the page into a 1280 CSS pixel ICB, why isn't the video visually zoomed in (such that its right and bottom parts, including the bottom bar, are offscreen)? That's what I would expect the rendering to be in this state (and if that _were_ the rendering, the underlying bug would be much more obvious from the get-go).

The reason for this is that we [skip building an async zoom container](https://searchfox.org/mozilla-central/rev/95935109bbbd4a39d612a917e59025f9c81f9d76/layout/painting/nsDisplayList.cpp#877) if the document is in fullscreen mode. This was also introduced in bug 1696717.

It's a bit of a footgun that there exists a set of conditions under which we ignore `PresShell::mResolution` for rendering purposes (by not building an async zoom container), but still use it for hit-testing purposes. We may want to consider at least detecting and asserting if that ever happens when `mResolution != 1.0`. (Such an assertion would have caught this bug and made the problem obvious.)