There are registry keys for HierarchicalZ in OpenGL too. I just tested it now just to see that it works too:
800x600x32 (1024x768x32 turned Vsync on for some reason
)
HierarchicalZ on:
Overdraw/HSR:
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Overdraw factor 3, back to front: 460.61 fps
Overdraw factor 3, front to back: 1309.37 fps
Overdraw factor 3, random order: 737.59 fps
Overdraw factor 8, back to front: 168.31 fps
Overdraw factor 8, front to back: 1012.59 fps
Overdraw factor 8, random order: 456.17 fps
HierarchicalZ off:
Overdraw/HSR:
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Overdraw factor 3, back to front: 467.22 fps
Overdraw factor 3, front to back: 582.41 fps
Overdraw factor 3, random order: 530.34 fps
Overdraw factor 8, back to front: 169.35 fps
Overdraw factor 8, front to back: 226.57 fps
Overdraw factor 8, random order: 208.98 fps
These are the relevant OpenGL regkeys (all available in UniTuner)
disableHyperZ
enableHierarchicalZ
enableZCompression
enableFastZMaskClear
ZCompForAllConfigs