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Killer Game Programming in Java by Andrew Davison

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Displaying a Model

Once a model is loaded, it's displayed inside the scene. This simple task is complicated by the need to make sure that the model is positioned, oriented, and scaled so the user can see all of it.

I've simplified the problem by making some assumptions about how the model should be reoriented and scaled: a loaded model is always rotated clockwise around the x-axis by 90 degrees and scaled to be no bigger than 10 world units across. I don't bother repositioning the model since all the examples I tested were located close to the origin after they'd been scaled.

Why the rotation? Most of the models I'm using were created with 3D Studio Max, which uses a different axis system from Java 3D. The axes in 3D Studio Max use the XY plane as the floor, with the z-axis as the vertical; Java 3D treats the XZ plane as the floor and the y-axis as the vertical. The difference can be seen by considering a vector displayed in the two systems. The vertical vector (0, 0, 1) in 3D Studio Max will point forward in Java 3D (see Figure 16-5).

The vector (0,0,1) in 3D Studio Max and Java 3D

Figure 16-5. The vector (0,0,1) in 3D Studio Max and Java 3D

A model that's upright in 3D Studio Max will be displayed face down when loaded into a Java 3D scene. The solution? Rotate the model clockwise around the x-axis by 90 degrees to bring it back upright.

The rotation and the scaling operations are applied to the model via a TransformGroup node placed ...

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