Improved technology has made stereoscopic viewing, that is viewing stills and movies with separate left- and right-eye images to give apparent depth, better quality and and more common on computers and televisions. As far as SHAPE is concerned, there are two separate kinds of stereo-enabled video cards of the most recent types. At present, software stereoscopic drivers for these cards appear to be available only for Windows.
Direct3D stereo in Windows (only) is supported by the nVidia GeForce series of graphics cards,with their 3D Vision package, and perhaps some others. The GeForce series only supports Direct3D in stereo (not any kind of OpenGL).
The 3D Quad Stereo Drawing Mode is available only for graphics cards supporting OpenGL quad-buffered stereo. It is potentially supported for Macintosh and Linux as well as Windows, though driver software does not seem to be available yet for them. The Quadro series of cards from nVidia actually supports either Direct3D or quad-buffered OpenGL stereo.
With either type of video card there are basically two types of viewing hardware.
1) Shutter glasses. The images are drawn independently and flashed alternately on the screen at a high rate - 120 times per second in the latest computer implementations, for example those supported by both the nVidia Quadro and GeForce series of display cards. A 120 Hz monitor or projector is required, and it must be viewed with special shutter glasses which blank out the left and right eyes alternately in synch with the images on the screen. Projectors and projection TVs are also available.
2) Polarizing monitors or projectors. The monitor or projector simultaneously or alternately (very rapidly) generates two images which are view with glasses with the two lenses polarized at 90 degrees to each other, or with different circular polarizations. Movie theater 3D (stereo) systems use a more elaborate variant of this method. It does not require expensive shutter glasses, only relatively inexpensive polarizing glasses for each viewer.
These types of hardware stereo viewing are full-color and should not be confused with the old two-color (red-green) anaglyph technology which really only shows monochrome or bi-chrome images. SHAPE has always supported stereo viewing using two spatially separated images combined with the naked eye or an optical viewer - this type of technology goes back to the 19th century.
The terminology for stereo viewing can be somewhat confusing. In movie theaters and television, the term 3D means stereoscopic viewing, that is separate images for left and right eyes. In computer and video-game graphics, the term 3D has been applied to several kinds of software techniques, at present primarily OpenGL and Direct3D, which keep track, pixel-by-pixel, of the third dimension in drawings and thus typically produce more realistic images than 2D line and space-fill drawings, though they are not necessarily stereoscopic (no separate images for left and right eyes). This is the way the term 3D is used in all SHAPE literature. OpenGL and Direct3D may be used in SHAPE for single non-stereo images as well as stereo (2D images may also be shown as stereopairs with SHAPE, although this is usually inferior to using a 3D method).
SHAPE in the past has used only OpenGL, which is available for Windows, Macintosh and Linux . A special, full-screen Direct3D mode has been added to SHAPE for Windows to support stereo viewing with GeForce cards and any others which require Direct3D. This is selected only in the Display menu, or with a button in the Dialog Bar - Left, not in the Drawing Mode drop-down. SHAPE also supports stereo viewing using the quad-buffered OpenGL method, which is currently available on the Quadro series of video cards from nVidia and some other video cards.
Older Shutter-Glasses Systems
Older stereo display drivers from nVidia, which worked only on Cathode-Ray-Tube monitors, not flat-screen LCD monitors, supported Direct3D and OpenGL without quad-buffering. This system works with inexpensive shutter glasses, but if the refresh rate of the monitor is less than 100 Hz or so the flicker tends to be excessive. Such systems are basically outmoded and may not be supported by manufacturers.
Changes in operation of SHAPE
In order to keep the total number of options to a minimum, what were formerly Display Modes have now been separated into Model Modes and Drawing Modes. The Model Mode specifies the type of model which represents the crystal, and includes Standard, Ellipsoid, Cavities and Protein. The Drawing Mode specifies which computer technique and viewing mode is used, and includes 2D single, 2D stereopair, 3D single, 3D stereopair and 3D quad stereo. The 2D modes use essentially line and fill drawing, which is suitable for schematic drawings for publication, for example, though shading is available in SHAPE. The 3D modes use generally more realistic lighting and superior interpenetration relations, and usually look better on screen or in full-color high-resolution printed images. The OpenGL 3D system software is available on Windows, Macintosh and Linux.
An additional 3D mode, Direct3D, which is available only on Windows, is selected with a separate button or menu option. This is the Drawing Mode which is required for stereo viewing with nVidia GeForce display cards or any others which support Direct3D only. It is full-screen only (not windowed)
Selection of Stereo Viewing Methods
Simple stereo methods. These allow stereo viewing using no aids or inexpensive glasses or optical viewers. The stereopair modes allow stereo viewing with or without optical aids, but these modes have limitations; the stereopair modes halve the size of the image and the other image is always visible, giving three images (unless some special type of viewer is used).
Hardware stereo methods. In these methods a single image drawn by SHAPE is split into left- and right-eye images by the display hardware, or actually its resident software. Then the two images are displayed on screen, either alternating rapidly in synchrony with shutter glass, or as two differently polarized images. Any of several SHAPE Drawing Modes may need to be used, depending on your video card and monitor.
1) nVidia GeForce cards which support their 3D Vision system, and any other display cards which support only Microsoft Direct3D. Click on the Direct3D button in the Dialog Bar - Left or the Direct3D option in the Display menu. These cards will also display in anaglyph (red-green glasses) mode without shutter glasses or a special monitor. In this stereo mode, or any other except quad-buffered OpenGL, the program sends only a single drawing (or really, a 3D object) to the video card, which then rotates the image one way for the left-eye image and the other way for the right-eye image. nVidia drivers and most others have their own control for this rotation, which may be referred to as the depth or stereo separation adjustment. There is usually a "hot key" or combination for this, and there may be another which controls the actual physical separation of the images on the screen. The perspective distance, which controls the degree of nearness and also influences the stereo effect, is set by SHAPE and can be changed even in fullscreen mode with the SHIFT-P and SHIFT-[ keys (see below).
Setting up nVidia 3D Vision for Direct3D (DirectX). Some setup in the nVidia control panel may be required to enable adjustment of the convergence, which can be critical for satisfactory viewing. In the Control Panel, select Set up stereoscopic 3D in Stereoscopic 3D. Click on the button "Set Keyboard Shortcuts". If necessary click on "Show advanced in-game settings" and then check the box for "Enable advanced in-game settings". Instead of using the Increase and Decrease convergence hot keys, you can also change convergence by holding down the green-lit on-off button on the front of the nVidia IR emitter while rotating the adjustment wheel on the back of the emitter, but this is not enable unless the hot keys are enable here.
Adjusting perspective distance, convergence and depth. The nVidia parameter "convergence", adjusted with hot keys as in the previous paragraph, can have the effect of moving the object viewed forward or backward so that is in front of or behind the plane of the screen. However, for SHAPE it is usually best to have the center of the image roughly in the plane of the screen - this minimizes eye-strain and the prominence of "ghost" images. Thus the convergence hot keys should be used to cause the two images to coincide at the approximate center of the object. This is best done without wearing the glasses. Once this is done the convergence can be saved with a hot key (CTRL-F7). A convergence value is appropriate for a given value of perspective distance, so if you always use the same perspective distance (say 100 Angstrom), it should not be necessary to adjust convergence again. Once convergence is adjusted, the depth, which corresponds to the SHAPE parameter stereopair rotation angle, can be adjusted with hot keys to change the stereo effect. However, the perspective distance and convergence settings probably have more effect on the perceived depth. The SHAPE stereopair rotation angle is ignored in Direct3D.
2) Cards which support OpenGL quad-buffering, such as the nVidia Quadro series: Select the 3D quad stereo option in the Drawing Mode drop-down box in the Dialog Bar - Left or in the Display menu. Stereo can be shown either in a window or full-screen. The program itself sends the two completed images or objects to two separate buffers, so both the perspective distance and the stereo rotation angle ( = depth or stereo separation) are controlled by SHAPE; perspective distance is changed onscreen with the SHIFT-P and SHIFT-[ keys and the rotation angle with the SHIFT-A and SHIFT-S keys.
Setting up nVidia 3D Vision for quad-buffered OpenGL. In the nVidia control panel, select Manage 3D Settings in 3D Settings. In the Global Settings tabe, the Global presets option can be set to "3D OpenGL Stereo". It may then be necessary to select the particular setting Stereo - Display Mode and set it to "Generic active stereo (with NVIDIA 3D Vision)".
For full-color operation these options will also require either the nVidia 3D Vision shutter-glass kit and a compatible 120 Hz monitor, or a stereo polarizing monitor and polarizing glasses. Other hardware combinations may also be available.
3) Older nVidia cards or some other card with stereo driver software, a CRT monitor and shutter glasses. These may work with the Direct3D option as in 1) and/or with the 3D single option in the Drawing Mode drop-down box in the Dialog Bar - Left or the Display menu. This will only work in full-screen. Like Direct3D in 1) above, SHAPE sets the perspective distance but the stereo rotation is controlled by the video driver.
Shortcut keys for controlling SHAPE images. Since stereo images may require full-screen viewing in which menus are not available, the keyboard shortcuts for modifying or animating the images have been revised and extended.
Additional Details
The stereoscopic option for the video card may use additional shortcut keys to turn stereo on or off; to increase the counter-rotation of the left- and right-eye images; to change the separation of the two images; or to change other settings
It seems that nVidia cards, at least, produce a stereo effect only by rotation of the two images, rather than by themselves changing the perspective distance. SHAPE has a stereopair rotation angle settings, but these are used only in the quad-buffered OpenGL stereo mode, not the Direct3D mode (these angles are also used in the separate stereopair Drawing Modes, 2D stereopair and 3D stereopair). The physical separation of the two images may also be adjusted independently or in combination with the rotation. Thus in practice it may be necessary to adjust the rotation (which may be called depth or separation) with the video-card control, and the perspective distance with the SHAPE controls, by trial and error to get the optimum amount of stereo effect. The physical separation of the two images on screen, if that is an independent control, primarily affects comfort - if the separation is too large, the eyes may not be able to merge the two images. The controls supplied by the video card may have different names; depth, separation and/or convergence and the action of each may involve both translation of the image on screen and rotation. Considerable adjustment of these controls may be required to get the desired stereo effect and an acceptable level of comfort.
The major market for stereo viewing is for video games and movies, and the scenes viewed may extend to infinite distance and do not really have a center, as do the objects viewed in SHAPE. Thus the approach used for adjustment of the stereo parameters is somewhat different from what would ideally be used for SHAPE, and the settings for video games and movies may be considerably different from the ideal ones for SHAPE.
If the perspective distance is small in SHAPE, the projection of spherical atoms will be elliptical on the screen, and while this may actually be what the eye would see at a short distance, such a projected image is usually unsatisfactory in practice. Thus the perspective distance should usually not be decreased beyond the point at which atoms begin to look non-spherical.
Although the nVidia cards do not themselves change the perspective distance, there is no stereo rotation or stereo effect at all in Direct3D if the projection is orthographic rather than perspective - that is if Perspective is not selected in the Input 2 menu. Therefore, SHAPE always uses perspective projection in the Direct3D mode, with the perspective distance entered in the Perspective dialog (Input2 menu). If that distance is zero, a plausible value is entered based on the dimensions of the crystal.
In real life, viewing real objects with the two naked eyes, the stereo rotation angle is fixed by the perspective distance because the distance between the two eyes is fixed (approximately). Although the macroscopic crystals drawn by SHAPE may be viewed in the real world, the scaling is arbitrary, and it is generally easier to change the stereo parameter(s) than all the central distances. Changing the stereo rotation angle is equivalent to changing the interocular distance. Thus it is necessary to adjust the two parameters stereo rotation angle and perspective distance independently. SHAPE rotates structures about their own centers (at least if you choose automatic centering), so the physical separation of the images should not need to be adjusted in the quad-buffered OpenGL mode.
In real life when attention is directed to a near object, not only is each eye directed towards that object, but the focus is adjusted; viewing a near object causes distant objects to go out of focus or become blurred and vice versa. This enhances perception of depth. On a computer or movie screen the focus cannot be changed, and this may interfere with depth perception for some people. Of course everything drawn by SHAPE is always in focus, unlike a non-animated movie which is recorded by cameras which change focus like the eye. In SHAPE, you may select fog, which only fades out the colors from front to back and does not change the focus.
To review:
In Direct3D stereo viewing, you may need to make three adjustments; the perspective distance, in SHAPE; and the stereo rotation angle and image separation, with controls supplied by the video card. The terms used for the latter two may differ, and there may be interdependence of all three controls. With nVIDIA systems the convergence setting is closely related to the SHAPE perspective distance; keeping the perspective distance constant may make it unnecessary to readjust the convergence for every problem.
In quad-buffered OpenGL stereo, as well as the stereopair modes of SHAPE, both the perspective distance and stereo rotation angle are set in SHAPE. If Automatic Centering is selected (Input2 menu), the objects will be rotated about their own centers and it is not necessary to change the separation (separation of the two images in stereopair modes is determined by the size of the window or the screen).