Provided by: xscreensaver-data-extra_5.34-2ubuntu1_amd64 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 secs]


       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 visual.

       -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 details.

       -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 seconds.

       -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 magazine.