Improve scroll-to-zoom on web

[Wumpf]

The smaller the camera distance, the smaller the orbit camera movement via scroll wheel should be (3d space view)
This is already the case, but it's often still hard to accurately zoom in.

Demonstration of problem on Linux:

zoom_jump.mov

[jleibs]

This is very painful and makes the colmap demo nearly unusable on systems that only have a mouse with discrete zoom steps.

This is a single zoom "step" for me at the moment. I have no way to zoom to a level between "too far out" and "too close in."

[emilk]

Maybe related:

• Expose raw mouse wheel delta to allow alternative input emilk/egui#2718

[jleibs]

This has gotten somewhat better on native recently, but it's noticeably much much worse on web.

[jleibs]

This is still quite broken on web. Here's video of scrolling a single step with scroll-wheel on linux.

scroll.mp4

[emilk]

Here it is on Web on my Mac, scrolling one mouse step at a time (on my mouse):

It is pretty worrying that the wheel event acts so differently on different platforms. The eframe code handling this is platform agnostic:

https://github.com/emilk/egui/blob/073f49682da20828dbd118f1d97e14a2b3879631/crates/eframe/src/web/events.rs#L390-L438

Btw, why isn't the scroll smoothed @Wumpf? I know you added code for that, and if I scroll faster I get the smoothed behavior, but @jleibs doesn't. Perhaps he get many duplicates of the wheel events?

This is what I see under the "Inspection -> Input" panel in egui.rs when I scroll very quickly with a mouse wheel:

Here I get eight scroll lines in one go. If I scroll slower I only get one scroll line at a time (as expected).

If Linux is misbehaving we could consider special treatment on Linux, and just count the number of wheel events and ignore their magnitude (on Linux).

[emilk]

Please try #4668 on Linux and see how zooming feels these days

[Wumpf]

done!

[jleibs]

The above issues are still present:

This is one wheel click forward/backward:

2024-01-04.18-34-47.mp4

[jleibs]

Looks like for me the mouse wheel result is 180 but in units of Point instead of units of Line.

[Wumpf]

egui.rs also gives me points but shows +/- 13 for a single notch on the scroll wheel