Finishing Composite to handle transformed windows

[Keith Packard]

On Mon, 2006-01-09 at 12:37 -0800, Deron Johnson wrote:
> At one time there was a counter proposal to allow GLX attributes
> of a window be dynamically changed rather than requiring that a
> static configuration be selected up front. The static configuration
> proposal was adopted primarily because it dealt with the issue
> of what happens if the hardware doesn't support a particular
> configuration. It was felt that it is better to know that before running
> the application than getting partially into the initialization and then
> discovering that insufficient hardware resources are available.

Sure, I'm not suggesting that we switch to a dynamic configuration, only
that we allow the selection of a different static configuration for the
root window after it has been created, perhaps by associating another
GLX visual with the window in some fashion.

I was present when the existing GLX design was produced, but as I wasn't
deeply involved, I have only vague memories that there wasn't anything
aside from the window itself to carry the configuration information
about the GL resources. This isn't incompatible with my suggestion that
we allow applications to respecify which configuration should be used
with an existing window before the GL context is created. Essentially,
we tie another visual ID to the window to replace the configuration
specified by the default visual.

> But it is far, far too late to switch to a dynamic configuration
> approach now. That ship sailed long ago. The static configuration
> approach is now embedded in thousands upon thousands of OpenGL programs.

I'm not suggesting any incompatible change to GLX, only asking if an
additional mechanism might exist to make it possible to draw to the root
window with an application-specified configuration, rather than the
default (useless) configuration embodied in the typical default visual.

-keith

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