Vispy: avoid depth test when blending

[gselzer]

The vispy backend does depth testing for all blending modes, which, bluntly speaking, breaks transparency. This PR disables depth testing for blending modes where some sort of blending should occur.

[Copilot]

Pull request overview

Adjusts the Vispy backend blending setup to avoid depth testing for non-opaque blend modes, addressing transparency artifacts caused by depth testing during blending.

Changes:

• Update Vispy node blending configuration to disable depth_test for non-opaque blend modes.
• Update Vispy volume adaptor tests to assert the new set_gl_state(..., depth_test=False) calls.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/scenex/adaptors/_vispy/_node.py	Changes how GL state is set for blended modes by adding depth_test=False.
tests/adaptors/_vispy/test_volume.py	Updates blending assertions to match the new GL-state call signature.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

The test currently asserts the opaque transition calls set_gl_state(None, blend=False) without restoring depth testing. If the implementation is updated to explicitly re-enable depth testing for BlendMode.OPAQUE (to avoid state leaking from prior translucent/additive modes), this assertion should also require depth_test=True so the regression is covered.

Suggested change

	adaptor._vispy_node.set_gl_state.assert_called_with(None, blend=False)
	adaptor._vispy_node.set_gl_state.assert_called_with(
	None, blend=False, depth_test=True
	)

[Copilot]

When switching from a blended mode (where you now set depth_test=False) back to BlendMode.OPAQUE, the current call set_gl_state(None, blend=False) does not explicitly restore depth_test=True. In vispy, set_gl_state updates the stored GL-state, so omitting depth_test here can leave depth testing disabled for opaque rendering after a mode toggle. Explicitly set depth_test=True (and consider also restoring other depth-related state if needed) in the opaque branch, or use the appropriate vispy preset that re-enables depth testing.

Suggested change

	# for opaque, we need to disable blending
	self._vispy_node.set_gl_state(None, blend=False) # pyright: ignore
	# for opaque, we need to disable blending and restore depth testing
	self._vispy_node.set_gl_state( # pyright: ignore
	None, blend=False, depth_test=True
	)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.41%. Comparing base (50076c9) to head (591b2eb).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #69   +/-   ##
=======================================
  Coverage   88.41%   88.41%           
=======================================
  Files          62       62           
  Lines        3074     3074           
=======================================
  Hits         2718     2718           
  Misses        356      356           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.