Fix touchpad swipe/pinch and mouse wheel scroll behaviour

[Nidrax]

• Two-finger trackpad swipes (precise wheel events) now always freely pan the viewport on both axes, instead of behaving like mouse wheel notches (vertical swipe zooming, horizontal swipe panning).
• Pinch gesture zoom stays free/continuous by default; holding Ctrl while pinching now snaps to the nearest integer zoom level.
• Regular mouse wheel scrolling is now consistent between the vertical and horizontal axes: both pan by default, or both zoom when Ctrl is held (or vice versa if "Zoom with scroll wheel" is unchecked), instead of vertical wheel zooming while horizontal wheel/shift+wheel panned.
• Removed the now-obsolete "Zoom sliding two fingers" preference, since swiping always pans.

Fixes #11

Co-authored-by: Claude noreply@anthropic.com

[Nidrax]

@claude doesn't seem to be working when I test it on my MacBook Pro.
Can you cross-compare it with this proposed change to understand the context better and then commit an update: LibreSprite@6fd4572 ?

[claude]

Claude finished @Nidrax's task in 8m 11s —— View job

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Findings and fix

• Gather context (PR diff, current state_with_wheel_behavior.cpp)
• Review macOS improvements: trackpad gestures, menu search, and toolbar badges LibreSprite/LibreSprite#581 (the linked commit) for approach
• Diagnose why swipe/pinch/wheel behavior isn't working on macOS trackpad
• Implement fix
• Commit and push (can't build/run on macOS from this environment — see note below)

Root cause: the new pan/zoom logic in src/app/ui/editor/state_with_wheel_behavior.cpp (added by this PR) branches on msg->preciseWheel(), but that flag is set exclusively by the native, non-SDL2 Cocoa backend (src/she/osx/view.mm). Besprited's default build (USE_SDL2_BACKEND=on) uses src/she/sdl2/she.cpp instead, and its SDL_MOUSEWHEEL handler never called setPreciseWheel()/setPointerType() at all — so preciseWheel() was always false, on macOS and every other platform. Two-finger swipes therefore always fell into the "regular wheel notch" branch (zoom on vertical, pan on horizontal) instead of free-panning. On top of that, SDL2's Cocoa backend never forwards trackpad pinch as any SDL event, so onTouchMagnify never fired either — pinch-zoom was simply inert, matching what @Nidrax saw.

This lines up with what LibreSprite#581 independently found and fixed for their SDL2 backend.

Changes pushed (src/she/sdl2/she.cpp, src/she/sdl2/sdl2_display.cpp, src/she/CMakeLists.txt, new src/she/osx/magnify_gesture.mm):

• she.cpp's SDL_MOUSEWHEEL case now sets preciseWheel/Multitouch pointer type: via SDL's preciseX/preciseY fields (SDL ≥ 2.0.18) on non-Apple platforms, and unconditionally on macOS (mirroring macOS improvements: trackpad gestures, menu search, and toolbar badges LibreSprite/LibreSprite#581's reasoning — virtually all Mac scroll input is trackpad-originated, and pinch is the dedicated zoom gesture).
• Added osx/magnify_gesture.mm, which swizzles magnifyWithEvent: on SDL's own content view (SDL2 never forwards this gesture) to queue TouchMagnify events — ported from macOS improvements: trackpad gestures, menu search, and toolbar badges LibreSprite/LibreSprite#581's approach and adapted to reuse Besprited's existing she::Event/TouchMagnify plumbing (the same one the native osx backend's view.mm already uses), rather than copying their bespoke Objective-C event struct.
• Wired osx_magnify::init() into sdl2_display.cpp next to the existing tablet-support init, and gated the new file in CMake to APPLE AND USE_SDL2_BACKEND (the native backend already implements magnify directly).

I deliberately did not port LibreSprite#581's unconditional removal of the horizontal-scroll delta negation — that part of their patch touches all platforms without an explained rationale, and flipping it blind risks inverting horizontal wheel scroll on Linux/Windows. If horizontal direction still feels wrong on your Mac after this fix, it's a one-line, well-scoped follow-up.

Limitation: I can't build or run Besprited on macOS from this environment (Linux sandbox, no Xcode/macOS SDK, and the system CMake here is too old for this repo's cmake_minimum_required anyway), so this is reviewed carefully but not compiled/tested on real hardware. Please build and test on your MacBook Pro and let me know if swipe-panning and pinch-zoom now work as expected.

Branch: claude/issue-11-20260705-1241