Add a zoom API for CameraController

[gselzer]

We will want some programmatic way to say "zoom in this camera X amount" (see, for example, how ndv does it here).

An important question to ask, though, is what it means to zoom, beyond just "make things smaller/bigger". Depending on the context, "zooming" could mean:

• Widening the FOV (common for orthographic projections, although possibly useful for perspective projections too)
• Moving the camera away (common for perspective projections, useless for orthographic projections)

This PR hypothesizes that this behavior will be specific to the CameraController, adding CameraController.zoom(camera: Camera, factor: float, center: Position3D | None) -> None to its API. There is an implication here that you'll need a CameraController (either PanZoom or Orbit impls exist right now) to zoom, but I think that's okay.

[Copilot]

Pull request overview

This PR introduces a public CameraController.zoom(camera, factor, center) API so zoom behavior can be controller-specific (e.g., PanZoom scales projection; Orbit moves camera toward/away from its focal center).

Changes:

• Add CameraController.zoom(...) abstract method and implement it in PanZoom and Orbit; refactor wheel handling to call the new API.
• Expand/rename camera controller tests to cover both mouse-wheel zooming and the new public zoom() method (including center anchoring and axis locks).
• Add explanatory comment to orthographic projection regarding right-handed coordinates and Z-axis flipping.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 6 comments.

File	Description
src/scenex/model/_nodes/camera.py	Adds the zoom() API to controllers and routes wheel events through it for PanZoom/Orbit.
tests/model/_nodes/test_camera.py	Renames tests for clarity and adds new test cases for the public zoom API and Orbit scroll behavior.
src/scenex/utils/projections.py	Documents the Z-axis flip in orthographic projection for right-handed coordinates.

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[Copilot]

These assignments create unused variables (zoom and desired_tform). Ruff enables F rules for tests, so this will fail linting. Remove the unused variables or use them in the assertion.

Suggested change

	zoom = interaction._zoom_factor(delta)
	desired_tform = snx.Transform().translated((0, 0, starting_dist))

[Copilot]

This test hard-codes assumptions about the camera's default projection/transform (scaled(..., -1) and camera_center = np.zeros(2)). This makes the test brittle if defaults change. Prefer deriving expectations from cam.projection/cam.transform captured before calling zoom().

Suggested change

	interaction.zoom(cam, factor, center=center)
	# Projection should be scaled
	expected_proj = snx.Transform().scaled((factor, factor, -1))
	np.testing.assert_allclose(cam.projection.root, expected_proj.root)
	# Transform should have been panned by the compensating amount
	zoom_center = np.array(center[:2])
	camera_center = np.zeros(2) # camera was at origin before zoom
	delta_screen1 = zoom_center - camera_center
	delta_screen2 = delta_screen1 * factor
	pan = (delta_screen2 - delta_screen1) / factor
	expected_transform = snx.Transform().translated((pan[0], pan[1]))
	before_proj = cam.projection
	before_transform = cam.transform
	interaction.zoom(cam, factor, center=center)
	# Projection should be scaled relative to the camera's prior projection
	expected_proj = before_proj.scaled((factor, factor, 1))
	np.testing.assert_allclose(cam.projection.root, expected_proj.root)
	# Transform should have been panned by the compensating amount
	zoom_center = np.array(center[:2])
	camera_center = before_transform.root[3, :2]
	delta_screen1 = zoom_center - camera_center
	delta_screen2 = delta_screen1 * factor
	pan = (delta_screen2 - delta_screen1) / factor
	expected_transform = before_transform.translated((pan[0], pan[1]))

[Copilot]

Spelling: "right-handned" should be "right-handed".

Suggested change

	# NOTE: In a right-handned coordinate system, the camera looks down -Z, so we need
	# NOTE: In a right-handed coordinate system, the camera looks down -Z, so we need

[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.39%. Comparing base (8758200) to head (2ac99e1).

Files with missing lines	Patch %	Lines
src/scenex/model/_nodes/camera.py	91.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #64      +/-   ##
==========================================
- Coverage   88.42%   88.39%   -0.03%     
==========================================
  Files          62       62              
  Lines        3075     3085      +10     
==========================================
+ Hits         2719     2727       +8     
- Misses        356      358       +2     

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