Provided by: xscreensaver-data-extra_5.15-2ubuntu1_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] [-duration


       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.

       -duration seconds
               How long to run  before  loading  a  new  image.   Default  120

       -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.

       -fps    Display the current frame rate and CPU load.


       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