Re: [Freeglut-developer] Direct vs Indirect Rendering Context

[Stephen J B. <sj...@li...>]

Richard Rauch wrote:
> On Tue, May 04, 2004 at 08:28:35AM -0500, Fay John F Contr AAC/WMG wrote:
>  [...]
> 
>>Finally, and this is independent of the other changes, I made "freeglut"
>>print a warning message if the application allows a direct context but none
>>is available.
> 
> 
> As a potential user of software that uses freeglut, I would again
> ask that this be something that can be disabled, or is disabled
> automatically on certain operating systems.  If the OS has never
> claimed to support hardware accelerated 3D rendering, the user
> probably knows this.

Direct versus indirect has little to do with hardware versus software
rendering.

A direct rendering context is one where the libGL library has direct access
to the underlying rendering mechanism.  An indirect context is one where
every single OpenGL command is converted into a message and transmitted
via the X windows command socket to the X server - and thence to the
underlying renderer.

Be it with software or hardware rendering, if you can't get a direct
rendering context then you probably have something incorrectly installed
UNLESS you are running the program on a remote computer and viewing the
results on your local system.  These days, that's an extremely unlikely
situation - and therefore almost 100% certain to be some kind of a
configuration screwup.

As for 'certain operating systems':  This only applies to systems running
X windows - and all systems running X should be able to generate a direct
rendering context if properly installed.

Right now, the only software renderer that works under X is Mesa - and Mesa
DOES support DRI (Direct Rendering Infrastructure) for software rendering.

Hence, no matter what OS you have, and no matter whether you have software
or hardware OpenGL, a direct rendering context *should* be available
if things are set up right.

As someone who supports a lot of OpenGL programs, I can tell you that it's
VERY useful to have a message to tell people that they have this problem.
In the early days of OpenGL under Linux, I was supporting TuxAQFH and TuxKart
- and I would get a LOT of email of the form:  "I have a really fast graphics
card - but Tux is only running at 10Hz - why?".   This is a hard thing to
diagnose at arm's length - and having that message come out would have helped
a LOT because I'd have been able to tell immediately that the user had his
machine set up incorrectly.

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