Sculpted Prims

FAQ

Q: What is a sculpted prim?

A: A "sculpted prim" is a prim whose shape is determined by a texture - its "sculpt texture". Sculpted prims can create organic shapes that are not currently possible with Second Life's prim system.

Q: What is a sculpt texture?

A: A sculpt texture is a standard RGB texture where the R, G, and B channels are mapped onto X, Y, and Z space. For those familiar with computer graphics - a sculpt texture is very similar to a normal map, but instead of encoding surface normals we encode surface positions. They are also similar to displacement maps, but instead of a single scalar distance we have three values (for each of X, Y, and Z.) They are also very similar to parametric (e.g. nurbs) surfaces.

Q: How can I make a sculpt texture?

A: The easiest way is to create a model in an external 3d package and use an exporter. We provide an exporter for Maya, and hopefully exporters for 3ds Max, Blender, and ZBrush will be available soon. We also have plans to provide a sculpt editor within the Second Life viewer.

Q: How detailed can a sculpted prim be?

A: Our current implementation samples the sculpt texture by different amounts depending on level of detail (LOD.) Prims which are close to the camera get a 32x32 grid of vertices, which drops to 16x16 grid as the prim moves away from camera, and so on.

Q: But why use textures (images) to encode shapes?

A: Because there are a myriad of existing tools for handling images. Image compression, streaming, progressive loading, and animation are all well-explored problems. For example - we could create a quicktime stream which fades from one sculpt texture to another - attached to a sculpted prim, the prim would "morph" from one shape to the other. Or, as another example - it would be easy to have a flash animation generate a sculpted prim - and when a resident touches a spot on its surface, the shape could wiggle and ripple appropriately. This is the direction we are headed.

Q: How big should my sculpt textures be?

A: We recommend you use a 64 by 64 pixel image. More data is really unnecessary - less can result in bad sampling when the sculpted prim changes LOD.

Q: How do sculpted prims work in the physics engine?

A: Currently, sculpted prims are approximated by a lopsided sphere having roughly the same size as the sculpted prim. In the future we may provide a more exact representation to the physics engine - thereby providing more realistic movement/collisions for sculpted prims.