Game Development Reference
In-Depth Information
focus, and the center set should appear to be three-dimensional. You can also get the
sets to fuse by crossing your eyes; however, this is much less comfortable than using
your eyes in their distance-viewing configuration.
Given that your brain is excellent at real-time pattern recognition, it can also compare
visual information over time to get a sense of size and relative distance. This is called
movement parallax , and it causes objects that are closer to you to appear to move faster
when you move your head than objects that are farther away. For example, if you are
driving in a car, you'll notice that the trees appear to move faster than the moon. This
is because the trees are very close in comparison to the moon. Your brain uses this
apparent speed disparity to help conclude that the moon is very far away indeed. In the
next chapter we'll discuss how computer algorithms attempt this sort of pattern recog‐
nition.
In fact, according to Flight Simulation (edited by J. M. Rolfe and K. J. Staples; Cambridge
University Press), the process of 3D visualization depends on the following eight major
factors.
• Occlusion of one object by another
• Subtended visual angle of an object of known size
• Linear perspective (convergence of parallel edges)
• Vertical position (objects higher in the scene generally tend to be perceived as far‐
ther away)
• Haze, desaturation, and a shift to bluishness
• Change in size of textured pattern detail
Stereopsis
Accommodation of the eyeball (eyeball focus)
A standard 3D graphics library is capable of giving the appearance of three dimensions
on the screen, just as any good painter on a canvas. Both standard 3D libraries and
painters do their job by recreating the first six items in the preceding list. To further the
illusion, 3D display technology simulates the seventh, stereopsis. Stereopsis is impres‐
sion of depth generated by the fact that you have two eyeballs looking at slightly different
angles. In short, the graphics library renders two different images, one for each eye, that
have a parallax shift. These images are then delivered to each eye separately. The method
by which the images are segregated varies from technology to technology. We will dis‐
cuss these in a little bit.
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