GTK shared memory extension support

The GTK-AGG combination supports the use of the X11 MIT-SHM extension. This extension allows passing image data to the X server in it's native format (defined by the graphics mode). This prevents CPU intensive pixel format conversions for the X server.

Not all X servers support this extension and it's available for local (not networked) X connections anyway. So the GTK GUI will first *try* to use the extension and on failure provide automatic fallback to standard pixmaps.

You won't notice this fallback unless you check the log messages (aside from potential performance difference.)

The macro ENABLE_MIT_SHM must be defined in gtk_glue_agg.h to enable support for the MIT-SHM extension.

For more information about the extension, have a look at these URLs: http://en.wikipedia.org/wiki/MIT-SHM http://www.xfree86.org/current/mit-shm.html

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