Types of Geometry

Geometry comes in many shapes and sizes. Despite what you might think, it also can be classified into many different forms. There is the traditional polygon or triangle that you are familiar with, but there are also other forms like a 2D image or text. In terms of the way that the scene graph is organised, they are all managed the same and effected by the same sets of attributes.

As you saw in the introductory chapter all geometry is added through the Shape3D class. It must extend the Geometry abstract class. Java 3D classifies geometry under four types:

1. Geometry arrays
2. Raster objects
3. 3d text
4. Compressed geometry

Raster information is a 2D mapping of image type data. It always stays parallel to the rendered window and is not effected by lighting. In a way, this represents a way of putting 2D text in a 3D window.

3D Text is just what it's name suggests. Pass it a string, font information and some depth information and it will extrude the string into real shapes in a 3D environment.

Finally, compressed geometry is a way of representing a highly optimised form of geometry. Instead of representing every point and connection, compressed geometry only keeps the most important relationships to maintain the basic features. This is really handy when creating extremely complex mesh shapes like faces and body scans.

Geometry Arrays

In each of the examples shown below, triangles are used as the basic shape. With Java 3D, and most other rendering APIs, it is possible to use more than just triangles. Points, lines and quadrilaterals may also be used.

Your basic unordered collection of geometry is demonstrated in figure 1. Note that each triangle is separate and that they don't share any common edges or vertices. Although they don't typically share information, that is possible. However, if you are, you are probably better off dealing with a different primitive type.

Figure 1: Simple triangles that aren't connected

Strips of vertices combine common edges and vertices together to form a long, connected surface as demonstrated in figure 2. Strips travel in any direction and may make odd turns etc. The area to watch for is that the triangles always form opposing pairs. Note that at each vertex you only ever see three triangles.

Figure 2: Strip of triangles

The last arrangement of geometry is a fan shape. One vertex (usually the first one in the list) provides a pivot point from where all the other vertices then join. Where a triangle strip may be able to cover large distances, the fan is generally reserved for creating conical and flat structures like circles.

Figure 3: A Fan of triangles from a central point

Rasters

3D Text

Compressed Geometry