But does it have to be so wangy?

Only 5 months between posts, I'm on a roll. It's hard to remember everything that I've done to actually make these two images.

This is the first round of an actual 3D rendering of the octopus leg that I was designing in January.





First off, I finished off wrapping all the Renderman functions for NURBS, patch surfaces (and subdivision surfaces, too, IIRC). I think pretty much all that leaves is functions which require passing in a pointer to a C function. Those are going to be a little tricky, but I have some ideas.

Next up, I took the two curves I drew in January and converted them to a parametric surface representation. Since one of the curves (the cross section) was actually two curves, one the mirror of the other, I had to do some tricks to convert it into one curve. I had hoped to figure out a method for concatenating arbitrary NURBS, but could only come up with a solution for the case where the endpoints are coincident and the end knots have full multiplicity. I think a general case might be possible, but I didn't want to spend too much time on it unless I really needed it.

Finally, when generating the test images, I found I needed to be able to position the camera arbitrarily. It's easy enough to come up with a basis matrix for a camera at a given position and looking at a certain point, but Renderman expects the inverse of that matrix. I guess it was also easy enough to generate an inverse of that matrix since the basis is orthonormal, but I figured I would probably need full matrix inversion at some point, so I decided to write a full matrix inverse routine. That turned out to be a lot harder than expected.

End result: I can draw arbitrary curves and surfaces, and position the camera wherever I want. Next up: figuring out shaders so I can draw something other than this lovely shade of matte blue, or figuring out animation so I can actually have something that, y'know... moves.