🚀 go-pugleaf

I have a question regarding vertical retrace for the DECStation
5000/200PXG and PXG Turbo.  We are trying to display images without
glitches and with very precise timing.  It seems to me that the most
straightforward solution would be to determine when vertical retrace
is occurring, and write into the frame buffer during that time.
Is this possible?  If so, then how is this determination made, and
how can the frame buffer be accessed directly?  Note that we are
X/Phigs/PEX novices, and know next to nothing about our hardware
except what the technical overview says.  I am willing to work to
understand the lowest levels necessary to do the job properly,
though.

Here's something that might shed light on our problem.  We have used
XCopyArea to copy pixmaps to the window, and that seems to get around
the glitch problem, but the images get displayed on the screen at
too-long intervals.  Does XCopyArea take note of vertical retrace, and
if so, why does it seem to operate slower than the refresh rate would
allow?

Thank you -- anoop@ptolemy.ss.uci.edu