Feedback on GL_EXT_texture_from_pixmap

[Ian Romanick]

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Deron Johnson wrote:

> My biggest concern is about the statement that clients need to rebind
> in order to get the latest pixmap contents for use by texturing. This
> seems to be an accomodation for devices which copy on BindTexImage.
> I'm mostly interested in getting excellent performance on devices which
> don't do a copy. Forcing clients to go through an expensive rebind
> transaction when it is not necessary for a device seems like an
> unnecessary slow-down. Perhaps one way of addressing this is to
> indicate to the user in the FBconfig whether the device is going to
> do a copy so that the client can rebind or not.

I've had similar thoughts about optimizing the common case, but I think
this is a bad approach.  The problem is that requires apps to have
conditionals sprinkled throughout their code.  The odds are pretty good
that one will get missed, and the app will work on the developer's
machine but fail on a user's.

I think a better approach is to have an explicit call such as
glXSyncTextureFromPixmap.  On cards that copy from the pixmap to the
texture this will trigger a copy.  On cards that do not require the
copy, it will be a nop.

Thoughts?

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