NV-driver Linux cannot-get-Z-buffer for legacy-OpenGL

Gaming and Visualization Technologies APIs OpenGL
1

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Gtk3 + GLX cannot get Z-buffer - only 2D;
The driver nouveau works fine.
See minimal-code-program

(build with make -f gtk3_glx.mak - using gtk3_glx.c)

Tested on:

  • NV-Driver 390.144

  • and NV-Driver 460.91.03

  • and NV-Driver 470.86
    firmware: nvidia/470.86/gsp.bin
    alias: char-major-195-*
    version: 470.86

  • on Ubuntu 20.04.3 LTS (Focal Fossa) 64-bit and also Ubuntu 18;
    (Kernel Linux 5.11.0-43-generic x86_64)

  • with NVIDIA GeForce GTX 1050 Ti/PCIe/SSE2
    ‘’’