Zooming out has a layout jump

[juliushaertl]

Describe the Bug

When zooming out using the touchpad or using ctrl-scroll the position of the document changes

Steps to Reproduce

1. Zoom in
2. Move the cursor to the left or right part of the document area
3. Zoom out using Ctrl-Scroll or the touchpad

Expected Behavior

The document just zooms out and directly is in the center target position

Actual Behavior

The document is first zoomed out in the right side of the browser window and then there is a layout jump where it is centered

Screenshots

writer-zoom-out-jumping.webm

Additional Context

COOLWSD version: 24.04.1.2 (git hash: 85fc0fd8)
LOKit version: Collabora Office 24.04.1.2 (git hash: da505b6)
Served by: Arch Linux
Server ID: 7d563b2f

[juliushaertl]

I also noticed a very small layout shift when zooming in with ctrl-scroll/touchpad, sometimes more sometimes less, but there is a slight jump between stopping the zooming and when the actual higher resolution tiles are rendered

writer-zoom-jumping.webm

[juliushaertl]

This is also visible with the zoom buttons, small papercut issue there would be that you have to wait until the zoom action was performed and cannot easily click multiple times to zoom in a couple of times:

writer-zoom-jumping-2.webm

writer-zoom-click-fast.webm

[pedropintosilva]

Today's discussion:

• We could animate the jump (the jump that is already happening, that centers the document back in) could be a way forward, but might be tricky to get smooth
• or as @marcoambrosini and @juliushaertl said we could: Ideally zoom out to center once the visible part of document is no longer exceeding the viewport

[eszkadev]

We could do it also this way:
a) when document width is completely visible on the screen -> zoom out with document at the center
b) when document width is visible partially (large zoom level or small window):

• zoom out using "starting center",
• when we reach edge of the document to be visible - use as boundary, move used center of zooming animation more to the real center of the document
• when we reach point that full width of the document is visible - continue as in A)

[juliushaertl]

a) when document width is completely visible on the screen -> zoom out with document at the center

Note that this seems to be already the case, just not once you start zooming out with scenario (b)