1642494 - Scrollbar ends get pointy or flat when pinch zooming on mac

Status: NEW

(Core :: Panning and Zooming, defect, P3)

Description

[Jeff Muizelaar [:jrmuizel]]

i.e. the effect is what you would expect if we were taking an image of the entire scrollbar and scaling the whole thing to the match the desired size. However, the round ends of the scrollbar should remain unscaled all the time.

Comment 1

[Botond Ballo [:botond]]

Is this a transient (while zooming) or permanent (persists even when the zoom gesture completes) effect?

Comment 2

[Timothy Nikkel (:tnikkel)]

Transient.

Comment 3

[Timothy Nikkel (:tnikkel)]

It's harder to see but there is a corresponding flattening when you are zooming in, the pointyness happens on zoom out.

Comment 4

[Botond Ballo [:botond]]

In that case, this is a long-standing issue that has also been the case on mobile all along. Fixing it would require layerizing the ends of the scroll thumbs separately, and having more complex logic to async transform the parts.

I don't think this needs to block desktop-zooming-release; it's at best a follow-up nice-to-have.

Comment 5

[Timothy Nikkel (:tnikkel)]

It might be a more noticeable problem on desktop since screen sizes are bigger, seems like Jeff noticed it pretty quickly.

Comment 7

[Markus Stange [:mstange]]

Can we "fix" this by just repainting more frequently during pinch zoom? To repaint only the scrollbars and not the content during the more frequent paints, we could still throttle how frequently we update the content resolution and display port.

Comment 8

[Markus Stange [:mstange]]

We're currently moving to a world where we draw scrollbars as WebRender rectangle and border items everywhere. (On Nightly, today, we do this for scrollbars in content but not yet in chrome documents.)
Once we draw all scrollbars as WR items, and once we have WR everywhere, we could fix this by adding the WR scrollbar items from somewhere that gets called near the call to apz_sample_transforms. We do something similar for off-main-thread video today, where videos are "pipelines" and we replace the display list of those pipelines for each composite.