XQuartz X11 drawing speed is 14x slower
Submitted by Frank Delaglio
Assigned to Jeremy Huddleston Sequoia
Created attachment 120573 simple test of XDrawLine to probe drawing speed performance.
X11 drawing seems to be 7x slower when XQuartz "Preferences/Output" is not set to "256 colors". It is also generally slow compared to X11 performance on Linux.
Xquartz 2.7.8 / Mac OS X 10.11.1 / Mac mini (Late 2014, Intel Iris Graphics)
As long ago as Mac OS X Yosemite, some folks have reported graphics slowdowns, for example:
I also saw drastic slowdown in my own X11 applications, and recently discovered that it seems to be related to whether XQuartz is in TrueColor (24 bit) or PseudoColor (8 bit) mode. I think earlier versions of XQuartz might not have had this problem.
To test things, I made a simple X11 program, attached here, which calls XDrawLine() many times. On my Mac mini, the program takes around 42 sec on 8-bit color, and over five minutes on the default 24-bit color settings, which means the 24-bit case is more than 7x slower.
The same program run on Linux via a modest PC-based virtual machine with 24-bit color takes about 16 seconds ... I realize that this is not a direct comparison, but a factor of 20 difference in speed doesn't seem right.
I don't have access to other Mac systems, so I don't know exactly what combination of OS X version, XQuartz version, or hardware, seem to have this problem.
Attachment 120573, "simple test of XDrawLine to probe drawing speed performance.":