The xleft, xright, yhigh and ylow parameters determine the actual pixels to be ren-dered. They do not affect the scene or the view being rendered in any way, but rather, are used to render a rectangular portion of the view.
The rectangle selected must be valid. That is: 0 <= xleft <xright, and 0 <= ylow < yhigh.
Note that when specified in SDL, xright is an absolute number, but when speci-fied on the command line, <wide> is the number of pixels of width of the image (that is, xright – xleft). This is so SDL retains the same sense as previous versions and the same sense as the interactive package, while the command line behavior is consistent with all the framebuffer standalones.
