MIT-SHM
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The MIT Shared Memory Extension or MIT-SHM is a X Window System extension for exchange of image data between client and server using shared memory.
The basic capability provided is that of shared memory XImages. This is essentially a version of the ximage interface where the actual image data is stored in a shared memory segment, and thus need not be moved through the Xlib interprocess communication channel. For large images, use of this facility can result in some real performance increases.
Additionally, some implementations provide shared memory pixmaps. These are 2 dimensional arrays of pixels in a format specified by the X server, where the image data is stored in the shared memory segment. Through use of shared memory pixmaps, it is possible to change the contents of these pixmaps without using any Xlib routines at all. Shared memory pixmaps can only be supported when the X server can use regular virtual memory for pixmap data; if the pixmaps are stored in some magic graphics hardware, your application will not be able to share them with the server.
