How to send non-consumed scroll events back to the compositor?

[paulrouget]

In BrowserHTML, we want to go back/forward in history when the user swipe right/left, like in Safari:

When the user scrolls horizontally, left to right, events are sent to WR, which will scroll layers. If scroll doesn't happen, we want the events to be sent back to the compositor. And then we might dispatch these events to the browserhtml script thread.

Also - thinking about it, we might want to do that too for regular - consumed - scroll events (window.onscroll).

[paulrouget]

If I'm not mistaken, when frame.scroll() happens and nothing scroll, we end up here:

webrender/webrender/src/render_backend.rs

Line 244 in dfa4246

None => self.notify_compositor_of_new_scroll_frame(false),

So I imagine we could re-use new_scroll_frame_ready to pass non consumed events.

[paulrouget]

I think I got it working. Closing.

I'll reopen a proper issue and/or PR to support this.