Sculpted Prims: 3d Modeling Glossary

(This is work in progress)

Advanced Modeling Glossary

Sculpted prims: A new prim type in Second Life. A sculpted prim is a prim whose shape is determined by a texture - its “sculpt texture”. Sculpted prims will allow for custom and more complex shapes to be brought into SL and used in building.

Sculpt Texture or “sculpt map”: Sculpt Textures are image files that contain the data for the shape of a sculpted prim. A sculpt texture is a standard RGB texture where the R, G, and B channels are mapped onto X, Y, and Z space. A sculpt texture is very similar to a “normal map”, but instead of encoding surface normals we encode surface positions.

How can I make sculpted prims?
The easiest way is to create a model in an external 3d package and use an exporter. To start with, there's an exporter for the Maya modeling program (code available here). There are several tutorials for Blender as well. Support for other programs should come quickly and an in-world tool is planned “eventually”. Check the related discussion on the SL wiki for more details.

What is the recommended size for sculpt textures?
The recommended size is 64 by 64 pixels. Larger textures will be scaled down when you upload. This is also the default export size. (Discussion)

Can sculpt textures be created in Photoshop or other paint programs?
Not easily. However, given a pre-made sculpt texture and an understanding of how they work, you can use a paint program to manipulate them and achieve certain effects. Check the related discussion on the SL wiki for details.

Maps: 3D graphics lingo for “texture map”, or what most SL residents know as textures. The textures most SLers know and love are also known as “diffuse maps” or “color maps” within most programs; some people may also be familiar with “opacity maps”, “bump maps” and “normal maps”. You will also come across the term “UVW Map”, which is basically the data that defines how a texture appears on a model.

Polygon Modeling: The most common type of 3d modeling method used in games (including Second Life). The process involves the direct manipulation of polygons (triangles and quads), faces, vertices and edges to produce the desired shape.

Can polygon models be exported as sculpt textures?
Yes, with care and with some restrictions. See the SL Wiki for details.

What’s the maximum polygon count / number of vertices I can use?
Count the number of vertices instead of polygons. Up to 1024 vertices will be rendered by the client for any given object, so you should keep your model under that count. If you need more vertices, split your model up into multiple prims. For reference, a torus in SL has about 1000 vertices.

NURBS Modeling: NURBS is short for “Non Uniform Rational Bézier Spline”. This modeling method uses a series of curves and control points to define the model’s shape. If you have already worked with the Pen tool in Photoshop, Illustrator and similar programs, you’ve worked with Bezier curves in 2D. NURBS take the same concept into 3D. According to Qarl Linden, NURBS are the best thing to use for sculpt prims; it makes some sense since he worked most recently in movie special effects where NURBS are commonly used.

Can my 3D program do NURBS models?
NURBS used to be the feature that separated professional-quality programs from the rest, although that gap is narrowing to a degree. In general, Max, Maya and Blender all do both NURBS and polygons. Many common “free and easy” or low cost programs like Google Sketchup, Milkshape, Wings3D and gMax do not. Rhino3d is a commercial program (though considerably cheaper than Max or Maya) that specializes in NURBS modeling. Other programs, including free ones, are currently being discussed on the Wiki. The topic of “what program should I use?” is really a whole document in itself.