Affected versions

• 86.0a1 (20210113213439)

Affected platforms

• Windows 10x64
• Ubuntu 20.04
• macOS 11

Steps to reproduce

1. Open Firefox and https://playground.babylonjs.com/#ARN6TJ#5.
2. Scroll down using the mouse wheel.

Expected result

• Scroll is executed as expected.

Actual result

• Scrolling down once moves the object very far.

Regression range

• Last good revision: e897247f1afc2ccc6d25b44ad0b1830cac87386b
• First bad revision: 021dcc5231fb07764c68c12310e23e14a35527cd
• Pushlog:
  https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=e897247f1afc2ccc6d25b44ad0b1830cac87386b&tochange=021dcc5231fb07764c68c12310e23e14a35527cd

Notes

• Attached a screen recording.
• The issue can be reproduced on Firefox 85.0b8 and 84.0.2 as well if dom.event.wheel-deltaMode-lines.disabled:true.

So they try to handle DELTA_LINE here, but by the time that runs, I guess some other code that reads off the deltas runs like this.

However that seems like it should work (we should just stop reporting DOM_DELTA_LINE)... So I'll take a closer look when I have the time.

Chromium/WebKit browsers behave the same here. I filed https://github.com/BabylonJS/Babylon.js/issues/9799 for this with some details.