Fwd: Off screen GLX rendering is here

I caught this message on Apple's X11 mailing list.  I thought there was
a possibility that it might have some relevance for Chromium on Darwin.

-Sean

----- Forwarded message from "Torrey T. Lyons" <[email protected]> -----

Date: Thu, 02 Sep 2004 16:58:27 -0700
From: "Torrey T. Lyons" <[email protected]>
Subject: Off screen GLX rendering is here
To: [email protected]

One of the common complaints about Apple's X11 is that is does not 
allow off screen GLX rendering. I realized recently that there is a 
little known secret about XDarwin that allows off screen GLX 
rendering, while still maintaining super fast direct rendering. In 
its standard configuration XDarwin also does not allow off screen 
rendering but its back end GLX renderer can be changed.

Note: This will not work with Apple's X11. You can only get super 
fast direct rendering and off screen rendering with XFree86 4.4.0 or 
newer or X.Org X11R6.7 or newer on Mac OS X 10.3.x.

The trick is to use the following command in the Terminal and then 
restart XDarwin:

defaults write org.xfree86.XDarwin UseAGLforGLX 0

If this works the XDarwin startup info (normally written to the 
console) will have the line:

Loading GLX bundle glxMesa.bundle (using Mesa)

In this case Mesa will be used for all indirect GLX rendering instead 
of CGL. The advantage of doing this is that Mesa fully supports off 
screen rendering. At the same time most all on screen rendering will 
still be done with the superfast direct rendering you are used to 
with Apple's X11.

The price you pay for this is that any indirect rendering (from 
clients on other computers for example) will be much slower. 
Operating in this "split personality" mode has also not been well 
tested. I might expect some artifacts when resizing windows with GL 
contexts, but so far I have not found any. YMMV.

--Torrey
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----- End forwarded message -----

-Sean

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