# Purpose

I’m starting a blog to document my progress learning computer graphics, computational geometry, physical simulation and mathematics. I want to be able to look back on this blog several years in the future and be proud of my progress in these areas.

Mathematics and computer simulation are my strongest passions but I am dissatisfied with the progress I’ve made during the last three years since starting a full-time job in the software industry. Most of my time at work is devoted to developing tools to test complex software systems. While it surely takes solid software development practices and lots of logic to test software effectively, it requires very little geometric or continuous mathematics – something I dearly miss from my undergraduate studies.

I recently attended the 2012 Game Developer Conference in San Francisco where I participated in the full-day mathematics and physics tutorials on Monday and Tuesday. These tutorials gave a taste of several general techniques that interest me applicable to real-time simulation for games:

- dual numbers for efficient automatic differentiation of functions
- dual quaternions for a compact representation of rigid-body transformations
- support mappings for efficient collision detection of convex primitives using the Gilbert-Johnson-Keerthi distance algorithm
- half-edge data structure for efficient manipulation of geometric mesh data
- Voronoi shatter for physically simulated destruction of game environments

Of the above techniques, I am already familiar with dual quaternions for rigid-body transformations, especially regarding skeletal animation skinning.

I thought I would implement some of these other techniques. I immediately applied automatic differentiation to my signed-distance field raytracer to calculate the gradient of the distance field to provide a normal for the raytraced surfaces. Rather than use traditional dual numbers, numbers with a real component and a dual component, I used a slight variation with one real component and three orthogonal dual components, one for x, one for y and one for z. Thus, I was able to calculate the partial derivatives of the field in each of the three directions of space as an alternative to approximating the gradient with three symmetric finite differences. I’m still not sure whether the technique is more or less efficient, but I’ll perform some measurements.

I also began implementing a half-edge data structure for meshes for my C++ game engine, Dynamo. I used Google’s Protocol Buffer library to describe the data layout. Protocol Buffers allow me to conveniently edit a text file representation of my data, yet package that same data into an efficient binary representation as needed. It also provides a convenient generated API to access and manipulate the binary data in memory. I have a couple goals for this effort:

- add mesh modification capabilities such as face extrusion, subdivision, and slicing via cutting planes
- add pre-processed and dynamic Voronoi shattering to these meshes

Tonight, I stumbled upon a half-edge data structure implementation for Processing at www.wblut.com/2010/05/04/hemesh-a-3d-mesh-library-for-processing. I’m excited to explore this implementation to see if I want to incorporate any of its functionality into my fledgling library.

I intend to read www.gdmc.nl/publications/2007/Computing_3D_Voronoi_Diagram.pdf and implement an efficient Delaunay triangulation algorithm to use in computing a 3-dimensional Voronoi diagram for real-time shattering effects. I also want to explore a naive implementation that slices a half-edge mesh by the bisector planes between each point in the Voronoi point set, for comparison.

Well, that’s it for my first blog post. It’s almost 4:00 am.