This is a system environment variable, so you can query its value from Python easily.
It is probably a bug in VTK library. Using OpenGL core profile causes rendering errors (e.g., render window update is delayed) on some computers with Intel graphics cards, so we had to force using OpenGL compatibility profile. However, apparently, this causes this issue on some high-end NVidia graphics cards.
Hopefully this problem will go away if we update to latest VTK version. Until then you may use this workaround of explicitly setting OpenGL profile.
The delayed update bug only affects certain Intel graphics cards and driver versions (but those don’t have the MarkerStyle issue). If yours is not among those graphics cards then you can safely use a core profile without any adverse affects.
What graphics card do you have? Do you see any problems when you enable OpenGL core profile?
I do have a NVIDIA Quadro P5000.
It seems no problem for re-setting SLICER_OPENGL_PROFILE as core.
I was mis-led by a pixel-spacing setting, which I was trying to figure out what happens but failed.
You see, now I have an image which has a pixel-spacing 15nm (that means, 1.5e-5mm). I load this image to Slicer and it seems fine. But the mouse-scroll to change slices along views does not work (slower than usual, the slice-bar on the top of each view work fine though). So I try to put a fake pixel-spacing value as 1.5mm or even 0.015mm, it works fine to middle-mouse-button-scroll to browse slices along views.
This is what I was trying to ask you expertise to figure out in my next question. This issue may be reproduced by yourself , trying to use that famous MRHead image, if you set image pixel spacing as 0.001mm, it’s fine. but if you set image pixel spacing as 0.0001 mm, then you try mouse-scrolling where you may see my issue.