Why does Xprt not offer the MIT-SHM protocol extension ?
The MIT-SHM protocol extension is partially (XShmPutImage would work, but others like XShmGetImage and esp. XShmCreatePixmap cannot be implemented properly) incompatible to the way how some of the Xprint DDX are implemented. For example the PostScript, PDF, PCL and SVGprint DDX do not rasterize any images on their side – instead they convert the stream of X11 rendering instructions into the matching PDL instruction stream. Only the printer side will (finally) do the rasterisation of the output image. This is the basically the same reason why XGetImage does not work for those DDXs – and functions such as XShmCreatePixmap would be useless since drawing operations on the shared pixmap would not be applied to the application (e.g. Xprint client) as well.
