Provided by: xscreensaver-data-extra_5.04-4ubuntu1_i386 bug


       blitspin - rotate a bitmap in an interesting way


       blitspin    [-display    host:display.screen]    [-foreground    color]
       [-background  color]  [-window]  [-root]  [-mono]  [-install]  [-visual
       visual] [-bitmap filename] [-delay usecs] [-delay2 usecs]


       The blitspin program repeatedly rotates a bitmap by 90 degrees by using
       logical operations: the bitmap  is  divided  into  quadrants,  and  the
       quadrants  are  shifted  clockwise.   Then the same thing is done again
       with progressively smaller quadrants, except that all sub-quadrants  of
       a  given  size  are  rotated  in parallel.  So this takes O(16*log2(N))
       blits of size NxN, with the limitation that the image must  be  square,
       and the size must be a power of 2.


       blitspin accepts the following options:

       -window Draw on a newly-created window.  This is the default.

       -root   Draw on the root window.

       -mono   If on a color display, pretend we’re on a monochrome display.

               Install a private colormap for the window.

       -visual visual
               Specify  which  visual  to use.  Legal values are the name of a
               visual class, or the id number (decimal or hex) of  a  specific

       -bitmap filename
               The file name of a bitmap to rotate.  It need not be square: it
               will be padded with the background color.   If  unspecified  or
               the string (default), a builtin bitmap is used.

               If support for the XPM library was enabled at compile-time, the
               specified file may be in XPM format as well as  XBM,  and  thus
               may be a color image.

               The  *bitmapFilePath  resource  will  be searched if the bitmap
               name is not a fully-qualified pathname.

               If this option is specified, then the image which is spun  will
               be  grabbed  from  the  portion  of  the  screen underlying the
               blitspin window, or from the system’s video input,  or  from  a
               random  file  on  disk,  as indicated by the grabDesktopImages,
               grabVideoFrames,  and   chooseRandomImages   options   in   the
               ~/.xscreensaver   file;   see   xscreensaver-demo(1)  for  more

       -delay microseconds
               How long to delay between steps of  the  rotation  process,  in
               microseconds.  Default is 500000, one-half second.

       -delay2 microseconds
               How   long   to  delay  between  each  90-degree  rotation,  in
               microseconds.  Default is 500000, one-half second.  DISPLAY  to
               get the default host and display number.


       XENVIRONMENT  to  get  the  name  of a resource file that overrides the
       global resources stored in the RESOURCE_MANAGER property.


       X(1), xscreensaver(1), xscreensaver-demo(1), xscreensaver-getimage(1)


       Copyright © 1992, 1993, 1997, 2001 by Jamie  Zawinski.   Permission  to
       use,   copy,  modify,  distribute,  and  sell  this  software  and  its
       documentation for any purpose is hereby granted without  fee,  provided
       that the above copyright notice appear in all copies and that both that
       copyright notice  and  this  permission  notice  appear  in  supporting
       documentation.   No  representations  are made about the suitability of
       this software for any purpose.  It is provided "as is" without  express
       or implied warranty.


       Jamie Zawinski <>, 17-aug-92.

       Based on SmallTalk code which appeared in the August 1981 issue of Byte