NOTE: This project is on hold permanently... it was eating up too much of my life ;) It's still a good example of how to couple a WPF program with DirectX and OpenGL for 3D rendering. If others are interested in collaborating I'd come back to this or something similar.
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InsaneFX is a node-based special effects editor (written mostly in C#) and native runtime (written in C/C++).
It ships with (unoptimized) example renderers for DirectX 9 and OpenGL. To get the most of InsaneFX...