Game Development Reference
In-Depth Information
Cameras
We have all of this data in our 3D world, representing objects and other visuals that
we need to get onto the screen; however, how do we go about describing what is in
our limited view? For this, we need a camera. A camera in this case is a virtual rep-
resentation of our view into the world. It stores information about where we are, what
direction we are looking in, and how we need to transform the third dimension so that
it either looks real or useful. Using cameras, we can also define part of the gameplay.
Players will play a first person shooter (where the camera is in the head of the play-
er character) differently than a third person shooter, where the camera sits over the
shoulder of the player character. Back in
Chapter 2
,
Drawing 2D Sprites
, I described
the two different projections we use to do that transformation: the
perspective
and
orthographic
projections.
By combining all of the data into a single matrix, we have a nice and easy way to
transform all of the different vertices through the different spaces until we reach the
correct location on the 2D screen to display the pixels.
Now we will take a quick look at the different spaces, and how we can use a camera
to go from a collection of vertices to pixels on the screen.
The vertices begin in
Model Space
. This is a coordinate space where all of the ver-
tices are relative to an origin that was specified when the model was created. For
example, the origin of a character model could be at the center of its body; however,
that character may be nowhere near [0,0,0] when placed in the world. We can use
this space to work with the single model without worrying about the fact that we may
use this model at a distant location in the world.
These vertices are then transformed into World Space by using matrices derived from
the position, rotation, and scale of the model. Now we are putting this object in context
with everything else in the world.
Once it has its place within the world, we need to think about how to get everything re-
lative to the camera. The next step is to transform the vertices into View Space, which
is a coordinate space relative to the camera (the camera is at [0,0,0]).
Now that we have everything relative to the camera, we need to project the vertices in
front of us onto the 2D screen plane, which transforms the vertices into Screen Space
