Game Development Reference
Fig 2.10 Adding a new plane to the scene.
Step 25. Play to see the view from SphereCam play out on the big
screen in your scene. This technique can be used in your games for
surveillance cameras, minimaps, or reflections in mirrors or water.
While cameras can be used to create a number of different visual effects, they
are also important for optimizing a game's performance. For example, the
camera's view volume should not be considered a trivial setting. As mentioned
previously, all objects inside the view volume get drawn to the screen. The
more objects to be drawn, the slower the frames per second. Even objects
behind other objects and not noticeably visible will be considered by the game
engine as something to be drawn. So even though an object doesn't appear
on the screen, if it is inside the camera's view volume it will be processed.
Therefore, if you have a narrow back street scene in a European city where the
player will never see beyond the immediate buildings, the camera's far plane
can come forward to exclude other buildings that cannot be seen anyway.
Whether the camera is looking at an orthographic or a perspective view,
the coordinate system within the game environment remains the same.
2.3.2 Local and World Coordinate Systems
There are two coordinate systems at work in game environments: local and
world. The local system is relative to a single game object, and the world
system specifies the orientation and coordinates for the entire world. It's like
having a map for the local layout of a city versus the longitude and latitude
system used for the entire earth.