3.3.8 Display Form

     

 

The Display form controls many of the characteristics of the graphics display window. The characteristics which may be modified include:

• AA  - Turns antialiasing on or off. Antialiasing helps smooth out the sometimes jagged appearance of lines resulting from the discrete pixels used to represent a line on the screen. It is highly recommended to leave this on, but on some versions of IRIX (i.e., 6.3) antialiasing is known to be buggy.
• Depthcue  - Turns depth cueing on or off. Depth cueing causes the more distant objects to blend into the background color. This can help give a 3D effect when viewing in a non-stereo mode. Warning: There is a known bug that causes the antialias and depth cue buttons to stop working. The existence of the bug is known, but the solution is not (yet). Until this is worked out, it is suggested to not change the AA or Depthcue settings.
• Axes  - A set of XYZ axes may be displayed at any one of five places on the screen (each of the corners or the center) or turned off. This is controlled by the Axes chooser.
• Stage  - The Stage browser controls the stage, which is a checkerboard plane that can be located in any one of six places or turned off.
• Detail   - The degree of detail in the displayed image. Nothing: show nothing; Points : show everything as points; Wireframe : show only wireframe representation for spheres, cylinders, etc.; Flat : show a flat image (no 3D effects); Full : show complete detail. The performance increases as the level of detail decreases.
• Alt. Detail - Same as Detail, but for the display during mouse operations on the displayed molecules, such as rotation, translation and scaling. Since VMD redraws the screen often while the molecule is rotated, it is sometimes beneficial to set lower level of detail for the time of rotation for better performance.
• Perspective  - The view of the scene can be Perspective or Orthographic.   In the perspective view (the default), objects which are far away are smaller than those near by. In the orthographic view, both objects appear at the same scale.
• Stereo, Eye Sep, and Focal L  -   These controls set the stereo mode and parameters; stereo is discussed fully in chapter §. The Stereo chooser changes the stereo mode, while the Eye Sep and Focal L controls change the eye separation distance and the focal length, respectively.
• Lights  - The graphics display window can use up to four separate light sources to add a realistic effect to displayed graphical objects. The Lights On browser turns these light sources on or off. If the number is highlighted, the light is on, and clicking on it turns the light off. See section § for more discussion regarding lights.
• Clipping Planes (Near Clip and Far Clip)  - Clipping occurs when only the part of an image within a certain region of space is drawn. Only those parts of graphical objects which are between the near and far clipping planes are drawn. This feature is useful for viewing a slice of the molecule. The clipping planes also affect the depth cueing, if it is turned on. Objects at the near clipping plane are distinct while objects at the far clipping plane are indistinguishable from the background color.

  The positions of the clipping planes are changed with the Near Clip and Far Clip controls. It is not possible for the near clip to be farther away than the far clip. When using stereo, the near clip should be decreased, or even set to zero.

• Screen Height (H) and Distance (D) -     The screen distance parameter determines the distance, in `world' coordinates, from the origin to the display screen. If this is zero, the origin of the coordinate system in which molecules (and all other graphical objects) are drawn coincides with the center of the display. If it is less than 0, the origin is located between the viewer and the screen, while if it is greater than 0, the screen is located closer to the viewer than the origin. A negative value puts any stereo image in front of the screen, aiding the three-dimensional effect; a positive value results in a stereo image that is behind the screen, a less dramatic effect (but easier to see, for some people) stereo effect.

  The screen height, along with the screen distance, defines the geometry and position of the display screen relative to the viewer. The screen height is the vertical size of the display screen, in `world' coordinates. Each molecule is initially scaled and translated to fit within a 2 x 2 x 2 box centered at the origin; so the screen height helps determine how large the molecule appears initially to the viewer. This parameter is used mainly to configure the VMD display to the dimensions and position of a large-screen display, such as a projector, that may be used as a stereo display.

   

  Figure 3.17 describes the relationship between the screen height, the screen distance, and the world coordinate space.