OpenGI is a platform-independent open-source C-library for parameterization and Geometry Image creation, developed by Christian Rau. Geometry Images are a powerful, completely regular representation of triangular (or quadrangular) meshes, describing each vertex and its attributes as a pixel in one or more rectangular images and thus defining an implicit connectivity through neighbouring pixels. It can be understood as a next step after color and normal mapping, representing the whole model as a set of images. Due to its regularity this representation is extremely suitable for implementing mesh algorithms (e.g. LOD, Subdivision, Smoothing, ...) on the GPU.

This figure shows the typical OpenGI dataflow, where the ellipses represent user data and the rectangles represent major OpenGI operations. The user specifes the data for a triangular mesh as a set of vertex arrays and an optional index array. For this mesh valid parameter coordinates are computed and this parameterization is then used to sample the mesh's attributes into a set of images. But OpenGI can also be used for parameterization only, by reading back the parameterized mesh into a vertex-/index-array representation. You can also use the library for sampling only by giving the mesh initial parameter coordinates.

Features:

Platform-independent and Open Source
Easy to learn OpenGL-like syntax and programming paradigms
Working on 2-manifolds of arbitrary genus and with a variable number of boundaries
Implementing various parameterization algorithms, e.g. Mean Value Coordinates, Stretch Minimization or the original GIM algorithm by Gu et al.
Supporting multi-chart patchifications
Easy and hardware-accelerated creation of Geometry Images
Creation of images not only for geometry but various generic attributes
Detailed control and feedback of the whole parameterization and Geometry Image creation process
Tight integration with OpenGL for easy and efficient data sharing