[cairo] Rotations with Quaternions

[cecashon at aol.com]

These are a couple of 3d drawings using Cairo.

https://github.com/cecashon/OrderedSetVelociRaptor/blob/master/Misc/cairo_drawings/spring1.c

There is a spring that has 3d points and uses a 2x3 rotation matrix to get the 2d points to draw with. It also has perspective by adjusting the x and y values by the z value. Just played around with this a little. A cylinder that uses a 2x3 rotation matrix but doesn't clip on the z-plane. And a cube that uses a 3x3 rotation matrix since it needs to retain the z values for clipping. The cube uses a cairo_scale to give it a distance perspective in the animation. The 3d points are eventually mapped to the 2d screen so you can use cairo 2d transform functions.

Cairo is a 2d library but being able to do a few things in 3d might be helpful. Makes drawing and animation some fun also. I still have a lot to figure out with this though.

 

Eric
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