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

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.

-grab-screen

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.

-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 <jwz@jwz.org>, 17-aug-92.

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