[tgrushka]

Happy Disability Pride Month!

I am celebrating this occasion as a legally blind contributor to help improve the magnifier for the COSMIC user community.

Feedback and suggestions for revisions welcome.

Summary

This PR corrects the focal-point math in ZoomMovement::Centered and OnEdge (which broke and caused jumping at high zoom levels) and refreshes the stale focal point on zoom in.

Use of AI / references

• I used AI to assist in research of the focal point computation formulae for OnEdge and Centered modes.

• I co-wrote the final formulas with AI assistance and my corrections. I tested the formulas.

• I used the formulas found in KDE's zoom magnifier - link directly to zoom.cpp and converted them to Rust and the COSMIC focal point system.

Changes

• Remove unnecessary focal point precomputation in OutputZoomState::new, because it is now updated on first zoom in anyway.

• Do focal point computation in Local coordinates in update_focal_point to eliminate local-global conversion confusion / issues.

• ZoomState::update_focal_point

  • ZoomMovement::OnEdge branch - single code path rewrite - old two-branch logic caused jumping and unpredictability at high zoom. Fixes #2683, partially addresses #2688.

  • ZoomMovement::Centered branch - translation/clamp/invert - prevents "blow up" of calculation at zoom level > 2.0 that caused cursor to disappear off bottom right of screen. Fixes #1503.

  • is_level_change - sets previous_point so that animating_focal_point interpolates instead of jumping. Still room for improvement (needs focal point recomputation per-frame during animation to prevent "boomerang" feel), but this is still an improvement over jumping.

• In Shell::trigger_zoom, call ZoomState::update_focal_point when level > 1.0 - overlaps proposal in #1859 + the level gate to prevent stale focal point on zoom in. Fixes #2511 and #1883. Partially addresses #1420 (item 1 only).

• I have disclosed use of any AI generated code in my commit messages.

  • If you are using an LLM, and do not fully understand the changes it is making to the code base, do not create a PR.
  • In our experience, AI generated code often results in overly complex code that lacks enough context for a proper fix or feature inclusion. This results in considerably longer code reviews. Due to this, AI authored or partially authored PRs may be closed without comment.

• I understand these changes in full and will be able to respond to review comments.

• My change is accurately described in the commit message.

• My contribution is tested and working as described.

• I have read the Developer Certificate of Origin and certify my contribution under its conditions.

[Drakulix]

Code wise this looks good, just a couple of nitpicks. Obviously this will need to go through QA first, but thanks a lot for working on this!

[leviport]

Seems to be working nicely. Thanks!

[tgrushka]

Thanks for the reviews, @Drakulix and @leviport . Have I resolved the concerns and do you need anything else on this one? I just rebased and the clippy errors are in another module and unrelated to my changes. If the failing check is blocking, I can run clippy, if you want.

[Drakulix]

Have I resolved the concerns and do you need anything else on this one? I just rebased and the clippy errors are in another module and unrelated to my changes.

All good! Just needed to find the time to look into the code again. Thanks again :)