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       create_sub_zbuffer - Creates a sub-z-buffer. Allegro game programming library.


       #include <allegro.h>

       ZBUFFER *create_sub_zbuffer(ZBUFFER *parent, int x, int y, int width, int height);


       Creates  a  sub-z-buffer,  ie.  a  z-buffer  sharing drawing memory with a pre-existing z-
       buffer, but possibly with a different size. The same rules as for sub-bitmaps  apply:  the
       sub-z-buffer  width  and height can extend beyond the right and bottom edges of the parent
       (they will be clipped), but the origin point must lie within the parent region.

       When drawing z-buffered to a bitmap, the top left corner of the bitmap is always mapped to
       the  top  left corner of the current z-buffer. So this function is primarily useful if you
       want to draw to a sub-bitmap and use the corresponding sub-area of the z-buffer. In  other
       cases,  eg.  if you just want to draw to a sub-bitmap of screen (and not to other parts of
       screen), then you would usually want to create a normal z-buffer  (not  sub-z-buffer)  the
       size  of  the  visible  screen.  You don't need to first create a z-buffer the size of the
       virtual screen and then a sub-z-buffer of that.


       Returns the pointer to the sub ZBUFFER or NULL if there was an error.  Remember to destroy
       the ZBUFFER once you are done with it, to avoid having memory leaks.


       create_zbuffer(3alleg4), create_sub_bitmap(3alleg4), destroy_zbuffer(3alleg4)