web: Do not scroll the page when mouse wheel is handled in AVM2

[kjarosh]

This patch prevents scrolling the page when the users scrolls content inside the SWF (i.e. when the content somehow handles the scroll).

Based on my testing this behavior is a lot smarter than Flash originally had, because Flash just trapped mouse wheel events. We might want to add an option to simulate this behavior too in the future.

You can easily test the behavior here: https://www.newgrounds.com/portal/view/922049.

[Dinnerbone]

Oh no this is going to bring up the "where's the line" debate again :D

This does not match Flash's behaviour, AS3 mouse wheel events explicitly do not prevent the page from scrolling. It was a known trick to use AVM1 for scroll wheel stuff, which did prevent scrolling.

The linked page in original Flash does not prevent scrolling.

basilisk_6fNf97b3K3.mp4

[kjarosh]

So... I tested this a bit more, and I originally did tests with default params and assumed the result is always the same. Turns out the mouse wheel is trapped only when wmode is window, opaque, or transparent (not on direct, gpu). It's direct on NG, and it was window in my tests.

[torokati44]

Is this FP behavior consistent across browsers and platforms? 🤔

[kjarosh]

Is this FP behavior consistent across browsers and platforms? 🤔

Turns out this behavior differed across browsers and varied in time. We had a discussion about it on Discord, and I guess the bottom line was not to follow Flash Player in this regard.

Pasting some links from @n0samu:

• https://stackoverflow.com/questions/5477426/issues-with-wmode-opaque-and-issues-with-wmmode-window
• https://petethepig.blogspot.com/2012/02/handling-mouse-wheel-event-with-wmode.html