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Black Art of Java Game Programming by Joel
Black Art of Java Game Programming by Joel Fan Sams, Macmillan Computer Publishing ISBN: 1571690433 Pub Date: 11/01/96 Previous Table of Contents Next Projecting 3D Points on a Plane Projection means transforming 3D coordinates to a 2D plane. It is not as tedious as it sounds. All the 3D figures that you have seen thus far are actually 3D figures projected on a piece of paper. The software in our head can see the depth of a flat picture if it contains enough information. To help our brain see the depth without straining it too much, it is helpful to include objects that we know from real life, shade the polygons depending on the light source, and include shadows. A wire-frame model, for example, contains very little depth information, because we have no way of knowing which lines are in front of which. If you look at Figure 11-17 long enough, you will see what I mean. Figure 11-17 Wire-frame models contain very little depth information The art of 3D graphics is to pack so much information in a picture that the brain immediately perceives the depth. What you might not be aware of is that every time you look at a picture, your brain makes a massive number of calculations in order to approximate distances and perceive the depth, especially if the picture is taken in some environment unfamiliar to us. Fortunately, all the calculations are done behind the scenes without our noticing. For example, try driving your car on small streets with one eye closed. You will need to concentrate much harder, since the brain will start a thread that does all the calculation necessary to compensate for the loss of 3D sight. At this point you still have a perfectly rendered picture updated at 25 frames per second. Think of the problems you would have if you started blinking 10 times a second and were driving at noon, when there are no shadows, on a winding mountain road. You would probably end up over the side. One necessary piece of information that we definitely need to approximate distances is that objects are perceived as being smaller as they get farther away. This is the way we are used to seeing the world, and this kind of projection is called perspective projection. Although there are lots of ways to make projections, this type is the most useful to us, since it is the one that most closely resembles reality. The Screen Coordinate System (SCS)
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