How Do I Get It?You can download the source code or a command line 32 bit OS X app. There are caveats on both, so please check the readme files.
How Does It Work?An Arclight project has four main concepts: Layers, shapes, mods and arcs. Layers are the same as any paint program: Multiple layers are composited to create a final image. At the heart of each layer is a single shape. The only shape currently implemented is the humble circle. (all illustrations are labeled with the corresponding file name used to generate the image, included with the download)
For the arc to draw, we need a mod. A mod is a combination of a source and a destination. The source is responsible for getting information from the shape, then the mod takes this information and applies it to a destination in the arc.
Let's see an example. Here's our circle, but it now has a source set to the degree of each pixel from the center of the circle. In Arclight, degree 0 is the right edge, and it sweeps clockwise, so the lowest (0) and highest (1) values are the right edge, and the middle (0.5) value is the left edge:
Arcs can stack. This means we aren't limited to just using a Constant arc to shade the circle. If we want the shading to look a little more natural, we can run it through a pow() operation. Here's the circle, but now the Constant arc is being sent through pow(0.5) before shading the circle:
When shading the circle, there are four possible fill modes. Clockwise from top left they are INSIDE (shade starts inside the circle and ends at the edge), OUTSIDE (shade starts at the circle edge and proceeds outward), INSIDE/OUTSIDE (shade starts inside the circle and proceeds outside the circle) and EDGE (same as INSIDE/OUTSIDE except the center is not filled in; this mode will likely go away at some point). In addition to the fill modes, the following example prettifies things a little bit by adding a drop shadow, which is simply another layer beneath each circle built from the same components we've already discussed.