Woot! LTSP 5 + LDM over SSH (LDM_DIRECTX=False in lts.conf) + Open source radeon driver with AIGLX is working!
Nothing like running compiz smoothly on a dual monitor thin client :D
The problem I was having was that despite the X server on the thin client being fully configured and tested to use hardware acceleration locally, when connected to the terminal server over the secure LDM tunnel I was getting direct rendering with the software renderer which results in a big fail for compiz.
The key to avoiding the software renderer from being used for DRI was setting LIBGL_ALWAYS_INDIRECT=1 as an environment variable. I don’t know why with everything configured correctly that the system defaults to using the software renderer instead of indirect rendering + hardware renderer but at least forcing this environment variable in a global profile script allows for sexy hardware accelerated compiz goodness from securely connected thin clients.
Without the environment variable to force indirect rendering, glxinfo output with the LIBGL_DEBUG=verbose env variable set was complaining that the “drm device” didn’t exist. I suspect this is because glxinfo was expecting to somehow find the /dev/dri/card0 device on the terminal server itself instead of on the thin client and of course it doesn’t exist on the server… the OpenGL card is installed on the thin client!
There must be a way to get this working without the LIBGL_ALWAYS_INDIRECT environment variable but I couldn’t figure it out… this really smells of a hack but since it’s very easy to apply globally and it works just how I expect things to work, I’ll have to leave it in place until the time I can figure out another non-hacky way of getting the results I want with this configuration.