Game Development Reference
In-Depth Information
The last item on the list, accommodation of the eyeball, is the process by which your
eye changes shape to focus at different distances. By correlating the shape of your eye
with the distance to the object, accommodation works as one of the pieces of information
your brain uses to determine depth. As current 3D displays still use a 2D screen, the
eyes are still focusing on the same plane regardless of the object's perceived depth;
therefore, the eighth item in the list is not recreated. This is why most 3D displays still
do not seem completely real. Some technologies, such as holograms and volumetric
displays, allow for accommodation of the eyeball, but usually at the expense of some
other factor. We'll touch on these beyond state-of-the-art technologies near the end of
the chapter.
Stereoscopic Basics
There are some extra considerations when it comes using today's 3D display technolo‐
gies to recreate the images that would usually be provided to the visual cortex by bin‐
ocular vision. Normally two eyes create two images that the brain combines with a
biological depth map. The earliest stereoscopic images were generated in the 1800s from
two photographs taken from slightly different positions. The viewer would then look at
the photos through what came to be known as a stereoscope. This device was essentially
an early example of the View-Master that some of you might remember from childhood.
While the principle of showing unique images to each eye is straightforward in this case,
it doesn't allow group viewing and requires that the user have something pressed against
his eyes. To make 3D display something that a group of people can all experience to‐
gether and in some cases even without the aid of any headgear, we must look at some
more sophisticated methods of segregating the right and left images.
The Left and Right Frustums
If you are familiar with computer graphics, the concept of the viewing frustum is not
alien to you. If you aren't, we'll take a second to go over it, but it might be worthwhile
to read about it in detail before you continue. The viewing frustum is the region of space
in the model world that the camera can see from its given position in that world. In a
normal 3D graphic rendering, the frustum is clipped by a near plane that represents the
screen distance. In essence, you cannot render something closer to the user than the
screen plane. If you remember things jumping out of the screen in the last 3D movie
you saw, you can probably guess that when we are using stereoscopic rendering, this no
longer holds true. A normal computer graphics frustum is shown in Figure 24-2 .
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