XScreenSaver(1)

NAME
blitspin - rotate a bitmap in an interesting way

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

DESCRIPTION
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.

OPTIONS
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, it may come from an external video source: see below.)

-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.

RESOURCES
On some systems (currently, only SGIs), this program can, instead of grabbing a desktop image, grab a frame of video from an external camera and manipulate that instead. The following resources control that.

grabVideoProbability (Float)
    What portion of the time to grab video rather than a screen image, between 0.0 and 1.0. Defaults to 0.5, or half the time.

videoDevice (Integer)
    The number of the default video input device to check first. If unspecified, the default camera (from videopanel(1)) will be checked first. After that, all other available video input devices will be checked in order. The first one which produces a non-black image will be used. If all images are black, the others will be re-checked a few times before giving up and falling back to simply grabbing a desktop image (but note that this takes a few seconds, so if you don't actually have any video sources hooked up, you should consider turning off video grabbing by setting grabVideoProbability to 0.0.)

videoGain (Float)
    The amount by which to brighten the grabbed image. This defaults to 2.2.

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

SEE ALSO
X(1), xscreensaver(1)

COPYRIGHT
Copyright © 1992, 1993, 1997 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.

AUTHOR
Jamie Zawinski <jwz@jwz.org>, 17-aug-92. Based on SmallTalk code which appeared in the August 1981 issue of Byte magazine.