Exploring 3D in Flash - Flash 3D: Animation, Interactivity, and Games - page 2

What Flash does know how to do, however, is display vector shapes and calculate
expressions. With that, there is much that we can do if we are willing to look at 3D
from another viewpoint. In traditional three-dimensional computer graphics, 3D objects
are normally projected onto the monitor screen used as a picture plane. In many other
situations we interact in varying degrees with three-dimensional environments project-
ed onto a two-dimensional surface. This is true of photography, film, video, and many
fine-art paintings. We perceive three-dimensionality through visual and motion cues. If
we focus on the imagery as pictorial representations of 3D objects and spaces, we open
up a broad spectrum of potential exploration (Figure 1.1).
For example, we can create the illusion of 3D through a variety of drawing techniques.
The movement of objects themselves can produce a sense of 3D space. We can cre-
ate actual 3D objects, scenes, and animations in software packages outside of Flash
and then import the results into Flash. Even though layers in Flash are all at the same
distance to the viewer, we can use them to set up a rudimentary 3D space. We can use
ActionScript to dynamically create mathematically calculated three-dimensional spaces
and objects from scratch. And we can use combinations of each of these to create a
rich panoply of environments.
Flash is based upon 2D objects and positioning. Objects are always the same distance
from the screen. Movement in this depthless space is either left and right along the
horizontal or x-axis, or up and down along the vertical or y-axis, or along both axes.
To create a 3D space, there needs to be a sense of depth towards or away from the
screen. This involves moving along the z-axis. In Flash, the z-axis doesn't exist, so we
need either to find ways to simulate one or to mathematically define one. Exploring
ways in which this can be achieved is the purpose of this topic.
Types of Projections
Before we get into Flash 3D, let's look at the different ways in which objects can be pro-
jected as 3D drawings. All 3D drawings have four elements in common. They each have
1. a three-dimensional object
2. a picture plane for capturing the object's projected image
3. projection rays to project the object onto the picture plane's surface
4. a viewer to observe the object's image on the picture plane
The 3D drawing varies depending on the relationship between the projector rays and the
picture plane as shown in Figure 1.2. The projector rays can intersect the picture plane
in three ways, which produce different types of drawings discussed in the next section.