Java Programing

Texture coordinates themselves are usually manually calculated or are the product of an automated texture-mapping process (such as 3D model capture or model editor). Note that although we have called this section static mapping, there is nothing to prevent you from modifying the texture coordinates within a GeometryArrayat runtime. Very interesting dynamic effects can be achieved through reassigning texture coordinates. Care must be taken to ensure that texture images do not become too pixilated as they become enlarged and stretched by the sampling algorithm. The MIPMAP technique covered in detail in Section 14.3.4 is useful in this regard in that different sizes of different texture images can be specified. Needless to say, texture images consume memory, and using large 24-bit texture images is an easy way to place a heavy strain on the renderer and push up total memory footprint. Of course, the larger the texture image, the less susceptible it is to becoming pixilated so a comfortable balance must be found between rendering quality, rendering speed, and memory footprint. You should also be very aware that different 3D rendering hardware performs texture mapping in hardware only if the texture image falls within certain criteria. Modern 3D rendering cards typically have 16 MB or more of texture memory, and 64 MB is now not uncommon. Most rendering hardware will render texture images of up to 512 x 512 pixels. You should consult the documentation for the 3D rendering cards that your application considers important. 14.1.2 Dynamic mapping using TexCoordGeneration In contrast to a hard-coded static mapping between vertex coordinates and texture coordinates, dynamic texture mapping enables the application developer to define a mapping that is resolved by the renderer at runtime. Dynamic mapping is fairly unusual but is very useful for certain scientific visualization applications where the position of a vertex in 3D space should correlate with its texture coordinate. Rather than having to manually update the texture coordinate whenever a vertex moves, the application developer defines a series of planes that the renderer uses to calculate a texture coordinate. The TexCoordTestexample application explores the three texture coordinate generation options in Java 3D. These are TexCoordGeneration.EYE_LINEAR, TexCoordGeneration.OBJECT_LINEAR, and TexCoordGeneration.SPHERE_MAP(figures 14.6 14.11). Each will be described in turn in the sections that follow. 238

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