[cairo] Rotations with Quaternions

[cecashon at aol.com]

Hi Bill,

I took a look at your drawings of the checker pattern. They can be drawn with 3d rotations using quaternions. The rotations use a cairo transform so the drawing doesn't change how fonts are drawn. Nothing is changed internally in Cairo.

If you get a chance could you take a look at the following

https://github.com/cecashon/OrderedSetVelociRaptor/blob/master/Misc/cairo_drawings/rotation2.c

I have had some trouble getting the rotations to follow the "aircraft" spec but it is more a matter of how the axis are labelled for that. The drawing has a few squares that are rotated and their perspective changes along with the rotation. Similar to your checker board drawings.

Appreciate any comments.

Eric


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