New issue 1129: [experimental] Opaque sources fade volume sources
When opaque sources are rendered with ``alpha=1`` in default, the volume sources would not be visible.
In plane parallel lens, the objects in the middle are not visible.
In perspective lens, the entire volume sources are not visible.
New issue 1125: New VR interface needs moar answer tests
Right now, there are a lot of VR unit tests, but these basically just test whether you can run scripts to completion. They don't compare answers.
@ngoldbaum recently added a way to do answer tests like this, but people need to make more of them.
New issue 1123: Positions of opaque sources should be specifiable with units
Right now, `LineSource`, `PointSource`, etc positions must be specified as ndarray isntances and are assumed to be in code units. We should be able to specify these in an arbitrary unit system and then convert the positions to code units when needed.
Matt, Kacper and I will be at a workshop at UCSD Monday through Wednesday
next week. Should we delay the PR review hangout for a few days? Until the
week after? Would you guys feel ok doing the review hangout without us?
New issue 1121: [experimental] speed up PerspectiveCamera
Right now the PerspectiveCamera is about 4x slower than the PlaneParallel Camera in the VR interface. PerspectiveCamera is the most intuitive framework for doing VR since it behaves well to moving a camera in a volume and rotating that camera, and it would be great to use it as the default Camera. However, right now it is too slow to use for regular operations.