I'm back to my older Windows machine lately. I ran into the black screen in the viewport when I attempted to use the 0.19.17337 x64 LP 12.1.2 binary. I found an older nightly version, 0.19.16624 x64 LP 12.1.2, unzipped on the same machine and tested it.
The following older nightly (post .18 release) runs and opens files with no black screen in viewport
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.16624 (Git)
Build type: Release
Branch: master
Hash: 222ae7305fdf1097e4ef3d050f69dff47dbd8786
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)
However, the new version 0.19.17337 x64 LP 12.1.2 I tried yielded a black screen in the viewport.
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.17337 (Git)
Build type: Release
Branch: master
Hash: 0871fb49c71f1ac4029e441814332368f42bd78a
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/United States (en_US)
I have accumulated a reasonable collection of nightly build binaries; so, I can go back and check some builds post-16624 to find where abouts the change occured that now yields the black screen in the viewport on this machine. Unfortunately, the nightly collection is on my wife's laptop. I'll have to wait until I have access to it again to copy those binaries to this machine for testing.
Thankfully, WMayer's environmental variable suggestion, quoted below, has fixed the black screen on the new 0.19.17337 x64 LP 12.1.2. Nonetheless, I am curious as to which commit or change since 16624 has caused the problem. I'd like to find it and see if we can fix it - so long as the fix doesn't hinder FC's forward progress.
Thanks,
Russ