Sauerbraten 2007_08_19

Sauerbraten is an experimental engine based on Cube, can be seen as "Next-Gen Cube", or "Cube 2". Much like cube, the aim of this engine is not to produce the most eyecandy possible, but rather allow map/geometry editing to be done dynamically in-game, and make map editing a lot of fun.

Sauerbraten has an even simpler world model than cube (fewer exceptions, just one kind of building block), is quicker to edit geometry with, yet allows for significantly greater class of shapes. One way to see the transition from Cube to Sauerbraten is to say Cube was a 2-directional heightfield (floor and ceiling), and Sauerbraten is a 6-directional heighfield (heighfields can be modeled in all 6 directions).

The world consists of an octree of deformable cubes. It being an octree has just one important effect: it allows the mapper to work at any scale, from large landscape areas to small architectural details. The octree is largely invisible to the mapper though, he can arbitrarily break up larger cubes or merge them, and the engine takes care of the rest.

The deformable cubes are geometric shapes made out of maximally 8 vertices. In its maximum size, it is a regular cube that fills the entire octree node it sits in, as minimum size all 8 vertices coincide which is to say the cube is "empty". Anywhere in between theres a variety of slanted cubes and wedge shapes that are possible to any degree and orientation, and together with neighbouring cubes can form any shape easily.

The editor is similar to the one in Cube but much easier / direct to use, as there arent all the different kinds of cubes to worry about. Here, you can simply "push and pull" geometry with your mousewheel in 6 directions, depending on the orientation of the surface you are looking at. Modifier keys allow you to influence single vertices on a cube, connected vertices touching multiple cubes, edges, faces and entire cubes. Selections can be made to operate on more primitives at once. Many complex shapes are quick and easy to make. It is definitely the most fun way to model architecture to date.

The internal representation of a deformable cube is very different from a vertex based representation, and is based on "edge spans" which allows the engine to represent any kind of shape uniformly in just 12 bytes. This means it can hold great amounts of geometry in memory and maps on disk are small. To render this kind of geometry, the engine goes through a process of converting the internal representation to vertices using plane intersections based on the edge ranges, culls coinciding faces, merges vertices etc. to arrive at something which renders efficiently by hardware and caches this in chunks based on the octree. This allows Sauerbraten a significantly higher polygon throughput than Cube while maintaining its ability to have dynamic geometry.

The current implementation inherents all the non-world geometry related code from Cube, and as such works without modification: entities, AI, gameplay, network, console/script. For the new code, rendering and editing are close to done, physics and lighting are working quite well, level loading/saving is complete, SP & MP work, but plenty of more advanced stuff like occlusion culling & LOD is missing.

UPDATE: Sauerbraten has now started as a Cube community Open Source Engine (& Game) project. It interesting for developers & mappers, but maybe not players yet (though SP & MP do work). If you are interested in checking it out, or even in contributing, I suggest you visit the forums (see below).

NEWS: may 24 2005 release with lightmaps and working MP/SP gameplay! download from sourceforge below.