Stereo Viewing Notes

• Stereo
• Physical World
• Virtual World
• Render Statements

Stereo Viewing

Stereo viewing is where you trick your brain into thinking that it is viewing a real 3D object by presenting it with the two different perspective parallax views that your eyes would see. There are a number of different ways to output such an effect to the human visual system.

Physical World

The physical world is where the actual human observer resides. The human has two eyes which are offset from the center of his head in the X direction by some Eye Offset (EO). The viewer's head is

• Cross Eyed object appears closer
  
  See assignment 7 for more detailed notes about computing the frustum parameters for cross-eyed stereo.

• Diverge Eyed object appears farther away
  
• Red/Green Wire Frame object appears on the monitor, but glasses are necessary
  

Virtual World

• Oblique Frustums
  
• Rotated Cameras
  

SLIDE Render Statements

The following are Tcl variables which the renderer program maintains to run the simulation engine.

The global Tcl variables are:

• SLF_TIME: How much time has passed since the start of the simulation in seconds. Animations based on this variable may appear to be jerky if the rendering system can not maintain an adequate frame rate.
• SLF_FRAME: How many frames have been updated and rendered since the start of the simulation. Animations based on this variable may appear to slow down in time if the rendering system can not maintain a constant frame rate, but will keep constant spacing between frames which is useful if you are trying to render frames of an animations which you will later replay as a movie.

The Tcl variables allocated to each render statement tcltag use the following naming convention: SLF_tcltag_field. For a render statement which does not specify a tcltag the naming convention is changed to the following: SLF_field. The following are the tcltag based variables which the renderer currently maintains:

• SLF_tcltag_MOUSE_X: The X position of the mouse cursor in normalized coordinates of the last updated associated viewport.
• SLF_tcltag_MOUSE_Y: The Y position of the mouse cursor in normalized coordinates of the last updated associated viewport.
• SLF_tcltag_AXIS_X: The X component of the crystal ball axis of rotation maintained by the associated render statement.
• SLF_tcltag_AXIS_Y: The Y component of the crystal ball axis of rotation maintained by the associated render statement.
• SLF_tcltag_AXIS_Z: The Z component of the crystal ball axis of rotation maintained by the associated render statement.
• SLF_tcltag_ANGLE: The crystal ball's angle of rotation around the current axis in degrees maintained by the associated render statement.
• SLF_tcltag_SCALE: The zoom scale factor of the crystal ball maintained by the associated render statement.

To make a Tcl based crystal ball you then do the following:

group gRoot
  ...
endgroup

group gCrystalBall
  instance gRoot
    scale ( {expr $SLF_BALL_SCALE}
            {expr $SLF_BALL_SCALE}
            {expr $SLF_BALL_SCALE} )
    rotate ( {expr $SLF_BALL_AXIS_X}
             {expr $SLF_BALL_AXIS_Y}
             {expr $SLF_BALL_AXIS_Z} )
           ( {expr $SLF_BALL_ANGLE} )
  endinstance
endgroup

render vp gCameraRoot.instCamera.cam gCrystalBall
  tcltag BALL
endrender

References

• Computer Graphics: Principles and Practice, Foley, vanDam, Feiner, and Hughes, pp. 616-617}