@anthonykim1 can you pull the partial wheel tracking into CoreMouseService?

I just realized the scrolling experience differs alot when using trackpad vs. mouse when scrolling.
My scrolling speed for both mouse and trackpad is set to the median/middle in Mac system device setting.

I'm aggressively scrolling with mouse in the two videos:

Seems like better experience with mac trackpad, but bit too slow imo with mouse scrolling.

    // Fallback to WheelEvent.DOM_DELTA_LINE
    const targetWheelEventPixels = this._renderService.dimensions.device.cell.height / this._coreBrowserService.dpr;
    let amount = 1;
    if (ev.deltaMode === WheelEvent.DOM_DELTA_PIXEL) {
      amount /= targetWheelEventPixels + 0.0; // Prevent integer division
      this._wheelPartialScroll += amount;
      amount = Math.floor(Math.abs(this._wheelPartialScroll)) * (this._wheelPartialScroll > 0 ? 1 : -1);
      this._wheelPartialScroll %= 1;
    } else if (ev.deltaMode === WheelEvent.DOM_DELTA_PAGE) {
      amount *= this._bufferService.rows;
    }
    return amount;

Maybe the amount should be somewhere around 2 instead of 1? or wondering how should we handle mouse scroll vs. trackpad scroll.

@anthonykim1 I think you have vim mouse events off which is why it's scrolling more slowly? As discussed "1 line" scrolled ends up translating into 4 lines when vim mouse support is on, which was 4 times faster than how it should be scrolling.

The first video doesn't look great, could you look into what deltaY, deltaMode and targetWheelEventPixels are in your case? Different mouses/OSs behave differently.

@Tyriar I'm not sure, I just added set mouse=a to my .vimrc, but it still feels bit sluggish.

Two constant thing I found is that targetWhellEventPixel seems to always be 14 and deltaMode always seem 0

Here are more findings with mouse scroll:

• It also seems like deltaY should at least be absolute value of 103 in order to scroll to next element.
• If its a small scroll (deltaY abs(13)), then it seems to take MANY attempts to scroll to next).

Video for reference (only used mouse scroll):
https://github.com/user-attachments/assets/16fb95ee-999c-411e-acff-0251d8fdcbd8

I noticed that on trackpad where I have good experience, the deltaY is contained around MAX absolute value of 30, otherwise btw absolute value of 10.

Update: I think I got it.
Now mouse scrolling is very similar experience to trackpad