XScreenSaver(1)

NAME
sphereeversion - Displays a sphere eversion.

SYNOPSIS
sphereeversion [-display host:display.screen] [-install] [-visual visual] [-window] [-root] [-delay usecs] [-fps] [-mode display-mode] [-surface] [-transparent] [-appearance appearance] [-solid] [-parallel-bands] [-meridian-bands] [-graticule mode] [-surface-order order] [-colors color-scheme] [-twosided-colors] [-parallel-colors] [-meridian-colors] [-deformation-speed float] [-projection mode] [-perspective] [-orthographic] [-speed-x float] [-speed-y float] [-speed-z float]

DESCRIPTION
The sphereeversion program shows a sphere eversion, i.e., a smooth deformation (homotopy) that turns a sphere inside out. During the eversion, the deformed sphere is allowed to intersect itself transversally. However, no creases or pinch points are allowed to occur.

The deformed sphere can be projected to the screen either perspectively or orthographically.

There are three display modes for the sphere: solid, transparent, or random. If random mode is selected, the mode is changed each time an eversion has been completed.

The appearance of the sphere can be as a solid object, as a set of see-through bands, or random. The bands can be parallel bands or meridian bands, i.e., bands that run along the parallels (lines of latitude) or bands that run along the meridians (lines of longitude) of the sphere. If random mode is selected, the appearance is changed each time an eversion has been completed.

It is also possible to display a graticule (i.e., a coordinate grid consisting of parallel and meridian lines) on top of the surface. The graticule mode can be set to on, off, or random. If random mode is selected, the graticule mode is changed each time an eversion has been completed.

It is possible to define a surface order of the sphere eversion as random or as a value between 2 and 5. This determines the the complexity of the deformation. For higher surface orders, some z-fighting might occur around the central stage of the eversion, which might lead to some irregular flickering of the displayed surface if it is displayed as a solid object. For odd surface orders, z-fighting will occur very close to the central stage of the eversion since the deformed sphere is a doubly covered Boy surface (for surface order 3) or a doubly covered generalized Boy surface (for surface order 5) in this case. If you find this distracting, you should set the surface order to 2. If a random surface order is selected, the surface order is changed each time an eversion has been completed.

The colors with with the sphere is drawn can be set to two-sided, parallel, meridian, or random. In two-sided mode, the sphere is drawn with red on one side and green on the other side. In parallel mode, the sphere is displayed with colors that run from red to cyan on one side of the surface and from green to violet on the other side. The colors are aligned with the parallels of the sphere in this mode. In meridian mode, the the sphere is displayed with colors that run from red to white to cyan to black and back to red on one side of the surface and from green to white to violet to black and back to green on the other side. The colors are aligned with the meridians of the sphere in this mode. If random mode is selected, the color scheme is changed each time an eversion has been completed.

By default, the sphere is rotated to a new viewing position each time an eversion has been completed. In addition, it is possible to rotate the sphere while it is deforming. The rotation speed for each of the three coordinate axes around which the sphere rotates can be chosen arbitrarily. For best effects, however, it is suggested to rotate only around the z axis while the sphere is deforming.

This program is inspired by the following paper: Adam Bednorz, Witold Bednorz: "Analytic sphere eversion using ruled surfaces", Differential Geometry and its Applications 64:59-79, 2019.

OPTIONS
sphereeversion accepts the following options:

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

-root
    Draw on the root window.

-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.

-delay microseconds
    How much of a delay should be introduced between steps of the animation. Default 10000, or 1/100th second.

-fps
    Display the current frame rate, CPU load, and polygon count.

The following three options are mutually exclusive. They determine how the deformed sphere is displayed.

-mode random
    Display the sphere in a random display mode (default).

-mode surface (Shortcut: -surface)
    Display the sphere as a solid surface.

-mode transparent (Shortcut: -transparent)
    Display the sphere as a transparent surface.

The following four options are mutually exclusive. They determine the appearance of the deformed sphere.

-appearance random
    Display the sphere with a random appearance (default).

-appearance solid (Shortcut: -solid)
    Display the sphere as a solid object.

-appearance parallel-bands (Shortcut: -parallel-bands)
    Display the sphere as see-through bands that lie along the parallels of the sphere.

-appearance meridian-bands (Shortcut: -meridian-bands)
    Display the sphere as see-through bands that lie along the meridians of the sphere.

The following three options are mutually exclusive. They determine whether a graticule is displayed on top of the sphere.

-graticule random
    Randomly choose whether to display a graticule (default).

-graticule on
    Display a graticule.

-graticule off
    Do not display a graticule.

The following option determines the order of the surface to be displayed.

-surface-order order
    The surface order can be set to random or to a value between 2 and 5 (default: random). This determines the the complexity of the deformation.

The following four options are mutually exclusive. They determine how to color the deformed sphere.

-colors random
    Display the sphere with a random color scheme (default).

-colors twosided (Shortcut: -twosided-colors)
    Display the sphere with two colors: red on one side and green on the other side.

-colors parallel (Shortcut: -parallel-colors)
    Display the sphere with colors that run from red to cyan on one side of the surface and from green to violet on the other side. The colors are aligned with the parallels of the sphere. If the sphere is displayed as parallel bands, each band will be displayed with a different color.

-colors meridian (Shortcut: -meridian-colors)
    Display the sphere with colors that run from red to white to cyan to black and back to red on one side of the surface and from green to white to violet to black and back to green on the other side. The colors are aligned with the meridians of the sphere. If the sphere is displayed as meridian bands, each band will be displayed with a different color.

The following option determines the deformation speed.

-deformation-speed float
    The deformation speed is measured in percent of some sensible maximum speed (default: 10.0).

The following three options are mutually exclusive. They determine how the deformed sphere is projected from 3d to 2d (i.e., to the screen).

-projection random
    Project the sphere from 3d to 2d using a random projection mode (default).

-projection perspective (Shortcut: -perspective)
    Project the sphere from 3d to 2d using a perspective projection.

-projection orthographic (Shortcut: -orthographic)
    Project the sphere from 3d to 2d using an orthographic projection.

The following three options determine the rotation speed of the deformed sphere around the three possible axes. The rotation speed is measured in degrees per frame. The speeds should be set to relatively small values, e.g., less than 4 in magnitude.

-speed-x float
    Rotation speed around the x axis (default: 0.0).

-speed-y float
    Rotation speed around the y axis (default: 0.0).

-speed-z float
    Rotation speed around the z axis (default: 0.0).

INTERACTION
If you run this program in standalone mode, you can rotate the deformed sphere by dragging the mouse while pressing the left mouse button. This rotates the sphere in 3d. To examine the deformed sphere at your leisure, it is best to set all speeds to 0. Otherwise, the deformed sphere will rotate while the left mouse button is not pressed.

ENVIRONMENT

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.

SEE ALSO
X(1), xscreensaver(1)

COPYRIGHT
Copyright © 2020 by Carsten Steger. 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
Carsten Steger <carsten@mirsanmir.org>, 01-jun-2020.