Change zoom behavior so that zoom levels are always consistent

[ErikSwan]

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• I have searched the issue tracker for a feature request that matches the one I want to file, without success.

Is your feature request related to a problem? Please describe.
I zoom in and out very frequently when editing a diagram, either for general usability like making small adjustments in size or positioning or to verify that something is aligned to the grid.

The current zoom behavior in draw.io is strange and often frustrating for a couple of reasons:

1. The zoom levels in the toolbar dropdown menu do not align with the zoom levels when using Ctrl+(mouse wheel) to zoom.

   As an example of the consequences of this, if you pick 200% zoom from the dropdown menu and then use Ctrl+(mouse wheel) to zoom out, it's impossible to get back to exactly 100% zoom - the closest steps are either 115% or 95%.

   Likewise, it's impossible to reach exactly 200% zoom using Ctrl+(mouse wheel) to zoom in from the default 100% zoom - the closest steps are 175% and 210%. 200% zoom is preferable to either 175% or 210% because at 200%, things are drawn pixel-perfect (aligned to the pixel grid), but not at 175% or 210%, which results in slightly fuzzy lines and edges.

   Currently, the zoom levels in the toolbar dropdown are 25%, 50%, 75%, 100%, 125%, 150%, 200%, 300%, and 400%, but the closest corresponding zoom levels when starting at 100% and zooming using Ctrl+(mouse wheel) are 25% ✔, 50% ✔, 70% ❌, 100% ✔, 120% ❌, 145% ❌, 210% ❌, 300% ✔, and 435% ❌.

   This is strange and occasionally very frustrating.

2. When using Ctrl+(mouse wheel) to zoom, the steps sometimes get misaligned in the sense that it is impossible to get back to 100% zoom level by using Ctrl+(mouse wheel) to zoom back out.

   To reproduce this, start at 100% zoom, hold Ctrl, and scroll the mouse wheel up and down a bunch rapidly without releasing Ctrl. You'll find that at some point the steps get mis-aligned so that if you try to get back to 100% via the mouse wheel, you'll end up at e.g. 95%, 105%, 110%, or 115%, but it's not possible to get back to exactly 100%. This is a somewhat unrealistic use case, but it's the only way I've found to consistently reproduce the bug, and I can assure you I run into this all the time when just using draw.io normally and doing normal zooming in and out with the mouse wheel.

   Once again, this is frustrating because the zoom levels don't stay consistent, and because in order to get back to the default 100% you have to use the dropdown menu or the Enter keyboard shortcut.

   This one might be a bug, so some relevant details:

   • v26.0.2
   • Windows 10 Enterprise 22H2
   • Google Chrome Version 131.0.6778.205 (Official Build) (64-bit)
   • Yes. it's reproduceable in Incognito mode with no browser extensions.

Describe the solution you'd like
I would like the zoom system to be tweaked or reworked with the following principles in mind:

1. The exact zoom levels in the toolbar dropdown should be reachable when zooming with Ctrl+(mouse wheel).
2. When zooming with Ctrl+(mouse wheel), the zoom levels should stay consistent regardless of how many times or how far you zoom in and out.
3. It should always be possible to get back to exactly 100% zoom when using the mouse wheel to zoom.
4. When zooming in with Ctrl+(mouse wheel), integer multiples (e.g. 200%, 300%, 400%, 500%, etc.) should be included in the list of zoom steps/levels for the cleanest rendering.

Describe alternatives you've considered
What I propose might require re-architecting the entire zoom system or rendering engine. If that's too difficult, simply making the list of zoom steps in the toolbar dropdown match zoom levels reachable via Ctrl+(mouse wheel) would fix #⁠1 from above, and #⁠2 from above seems like a bug that might be easy to just fix.