Currently, there are plug-ins that enable the user to export directly from your 3D Application into Playstation, Sega Saturn, Nintendo 64, and Direct Draw formats. More plug-ins are always under construction to support the myriad of real-time formats being used in gaming.
Most pre-made, real-time 3D Application Programming Interfaces (APIs) provide a proprietary converter that works with the 3DS or DXF format (Free 3d max models). The geometry is exactly what you would expect: a list of numbered vertex positions in 3D space, followed by a list of how to connect these vertices into coherent polygons.
The normal (or visible solid) side of the polygon is determined either by the order in which the vertices that comprise the polygon are chosen, or by a separate list of vertex normals, also attached to the polygon construction list. Most real-time engines use triangular polygons, just as 3D Studio MAX ( Free 3D Max Models )does. Some systems use quadrilateral polygons.
Still other systems let you define quads and other types of polygons but break them down into triangles at rendering time. This can be a computationally expensive and unpredictable process. The best results seem to come from predefined triangular polygons. Although they require more storage than other polygons, predefined triangular polygons tend to render faster and always display as intended.
The.3DS file format exports only triangles, which is why it is so widely supported among real-time engines. Asmooth export of the source model into the game engine always proves a bit tricky and often requires a great deal of tweaking. High-powered modeling programs, such as your 3D Application, often add unusable information to the relatively simplistic real-time game engine. Most of this information is invisible (it may or may not be apparent when you look at the model in your 3D Application).
This information can have drastic effects on the exported real-time model, causing it to be drawn in the wrong orientation or position, or to behave improperly when animated in the game engine. The biggest trouble areas for export are generally the transform and the surface properties.
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