Thanks for the suggestions

Hardware gl seems to be fine, glxgears runs smoothly:

$ glxinfo | grep -i direct

direct rendering: Yes
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I'll follow up with more details soon, but I doubt volume of the data is the problem, it's quite modest by PDL standards, and when I'm using the "twiddle" mode to look-around an unchanging model there is no flicker. Previously I just had a mesh which seemed ok but when I used a filled sheet there is a noticeable flicker as the light sheet is draw over the dark background.

I might not need double-buffering exactly, but a GL equivalent that only draws once all the things to draw are queued.