Game Development Reference
Figure 24-11. Parallax budget
The budget scales with convergence distance and separation. You should make sure as
much of the important 3D action occurs between convergence and 10 times conver‐
gence. Your entire scene should be contained with negative convergence/2 to positive
100 times convergence.
In general, you must be most careful when trying to execute an out-of-screen effect.
These effects are very impressive to the viewer but cause the most eyestrain due to the
rapid change in parallax. Having the object first appear farther away than the screen and
then moving it closer to the user provides a context for the brain and encourages fusion.
If an object is going to be closer to the user than the screen, it is also important to prevent
that image from being clipped by the edge of the screen. That would make a portion of
the 3D object disappear, and the clipping always occurs at the convergence point. This
will give conflicting cues to the viewer and cause the 3D effect to be diminished. Given
the amount of control you need in order to prevent out-of-screen effects from causing
viewer discomfort, it is often best to use in non-player-controlled scenes.
Another difficult part of the game to render is the 2D elements. The user interface or
other menu items that have no depth are normally rendered at convergence depth.
However, there are some elements that are 2D but should be rendered at some nonzero
depth. The most important of these are mouse pointers and crosshairs. These should
be rendered at the depth of the object below them. This change in depth of the user-
controlled pointer helps maintain the idea that the objects are at different depths.
Passive stereoization takes the responsibility for managing the stereoization process out
of the programmer's hands. The programmer sends the render pipeline a single render
command as usual, and the GPU handles generating the stereo images. Most systems
rely on heuristic subroutines in the driver to take the monocular scene and generate
binocular images. A heuristic subroutine is one that attempts to give a computer “com‐