Coded, recoded, lost, recoded and recoded … hemesh, the half-edge mesh library for Processing has slowly accreted to a state that warrants a release. A release in more than one way. In retrospect, the current functionality looks depressingly small, especially compared to the hundreds of hours that already went into coding it. But like a broke home-owner with a basement and a half-finished first floor, I comfort myself with the thought that at least it holds potential for growth.

What is hemesh?

hemesh is an implementation of a half-edge datastructure for manipulating 3D meshes in Processing. Basically it’s a toolset to extend my Processing sandbox to a proper playground.

Generating and displaying a mesh requires nothing more than a list of vertices and a list of faces connecting them. This hardly requires a special dataset. However, manipulating a mesh in any but a trivial way requires a lot of connectivity information: neighboring vertices, neighboring faces, shared edges,… Keeping track of this in a simple facelist type structure is difficult. Hence the need for a datastructure that incorporates connectivity information in an efficient way: the half-edge mesh.

What can hemesh do?

The library is currently focused on the stuff I coded it for: 3D voronoi and random plane divisions. So with hemesh we can create 3D meshes. Several primitives are built-in, but any kind of 2-manifold mesh can be turned into a half-edge mesh from its vertices and facelist. The weight of the implementation lies in closed meshes but open surfaces are handled as well.

Creating meshes is cool (for a given amount of cool) but destroying them is cooler. Several modifiers are provided, either as part of the basic mesh functionality or as separate modifier classes. Subdividors are a special class of modifier oriented towards subdivisions. (The names might not be original but I guess it’s easier to remember than quaghot and umpsink.)

What hemesh can’t do…

The half-edge datastructure has a few limitations in itself. In practice, each edge in a mesh can be shared by at most two faces. The implementation is strongly face-based, isolated vertices and edges are not supported and will lead to ouchie.

The initial intent of hemesh was to build a system to prototype geometric play. So large-scale systems were never a goal. Several implemented algorithms are O(n²) and use a lot of storage. Connaiseurs and lectors in computational geometry are advised to avoid perusing the code, bleeding eyes often offend. On the positive side, there’s room for improvement…

Getting hemesh

The library is maintained at code.google.com. hemesh is currently at beta version 1.1.0 Download and extract the archive inside the Processing ‘libraries’ folder. The ‘hemesh’ subfolder contains several examples. A Processing version supporting JAVA 1.5 syntax is recommended, Rev 180 or higher. In the coming days, I’ll post some tutorials and spielerei to illustrate further use.

Future

At this time, the library reflects my current interests. If you want it to do something else, have a suggestion or hemesh goes haywire on you, let me know! One major addition is already planned: boolean mesh operations. This is a small step away from completion.