Bugzilla

I believe the desirable behaviour here is for the direction of the scrolling gesture to match physical directions on the screen.

So, on this page, since the element's scrollbar is physically horizontal, it should be a left/right swipe gesture that scrolls is, not an up/down swipe gesture.

This is largely the behaviour with APZ enabled (apart from the fact that you need an up/down gesture to initiate scrolling). The pre-APZ behaviour did not take into account transforms, which is why an up/down swipe is required in this case (since the element is vertically scrollable before transforms are applied).

Now, the fact that you need to start with an up/down gesture to initate scrolling, is a bug. It's related to macOS' "Swipe between pages" feature, which is why the bug is specific to macOS. Indeed, if you go to System Preferences --> Trackpad --> More Gestures and disable "Swipe between pages", scrolling now works with a regular left/right swipe, without needing to start with an up/down movement.

I suspect what's happening is that our code for determining whether an element is horizontally scrollable for the purpose of determining whether or not to enable the "swipe between pages" behaviour, does _not_ take transforms into account, but it should.

I believe the desirable behaviour here is for the direction of the scrolling gesture to match physical directions on the screen.

So, on this page, since the element's scrollbar is physically horizontal, it should be a left/right swipe gesture that scrolls it, not an up/down swipe gesture.

This is largely the behaviour with APZ enabled (apart from the fact that you need an up/down gesture to initiate scrolling). The pre-APZ behaviour did not take into account transforms, which is why an up/down swipe is required in this case (since the element is vertically scrollable before transforms are applied).

Now, the fact that you need to start with an up/down gesture to initate scrolling, is a bug. It's related to macOS' "Swipe between pages" feature, which is why the bug is specific to macOS. Indeed, if you go to System Preferences --> Trackpad --> More Gestures and disable "Swipe between pages", scrolling now works with a regular left/right swipe, without needing to start with an up/down movement.

I suspect what's happening is that our code for determining whether an element is horizontally scrollable for the purpose of determining whether or not to enable the "swipe between pages" behaviour, does _not_ take transforms into account, but it should.

I believe the desirable behaviour here is for the direction of the scrolling gesture to match physical directions on the screen.

So, on this page, since the element's scrollbar is physically horizontal, it should be a left/right swipe gesture that scrolls it, not an up/down swipe gesture.

This is largely the behaviour with APZ enabled (apart from the fact that you need an up/down gesture to initiate scrolling). The pre-APZ behaviour did not take into account transforms, which it's up/down gestures that cause scrolling in this case (since the element is vertically scrollable before transforms are applied).

Now, the fact that you need to start with an up/down gesture to initate scrolling, is a bug. It's related to macOS' "Swipe between pages" feature, which is why the bug is specific to macOS. Indeed, if you go to System Preferences --> Trackpad --> More Gestures and disable "Swipe between pages", scrolling now works with a regular left/right swipe, without needing to start with an up/down movement.

I suspect what's happening is that our code for determining whether an element is horizontally scrollable for the purpose of determining whether or not to enable the "swipe between pages" behaviour, does _not_ take transforms into account, but it should.

I believe the desirable behaviour here is for the direction of the scrolling gesture to match physical directions on the screen.

So, on this page, since the element's scrollbar is physically horizontal, it should be a left/right swipe gesture that scrolls it, not an up/down swipe gesture.

This is largely the behaviour with APZ enabled (apart from the fact that you need an up/down gesture to initiate scrolling). The pre-APZ behaviour did not take into account transforms, which is why it's up/down gestures that cause scrolling in this case (since the element is vertically scrollable before transforms are applied).

Now, the fact that you need to start with an up/down gesture to initate scrolling, is a bug. It's related to macOS' "Swipe between pages" feature, which is why the bug is specific to macOS. Indeed, if you go to System Preferences --> Trackpad --> More Gestures and disable "Swipe between pages", scrolling now works with a regular left/right swipe, without needing to start with an up/down movement.

I suspect what's happening is that our code for determining whether an element is horizontally scrollable for the purpose of determining whether or not to enable the "swipe between pages" behaviour, does _not_ take transforms into account, but it should.