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# Rotation Help

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My current project can be described as follows: The user is presented with a simple quad (that is stored internally with 4 vertices, 4 edges and 1 face, where the edges of the face are specified in CCW order. Then we allow the user to create an edge that divides the face in two. Probably think something like this: +-------+-------* | | | | | | | | | | | | +-------+-------* Through a trackball, we let the user orient this as they please. After division the user then clicks another vertex, say either of the ones marked with a *. Then as the user holds the mouse button down and moves it, the two vertices marked * are rotated along the axis that divides the two faces. This is where I am stuck. Every rotate-point-around-axis implementation out there has not given me what I want. I sat down and came up with a solution with matrices, but it still gave me bugs. This is simple but it''s giving me bugs, and consequently, driving me nuts. Any idea how to do this? Thanks, TT

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The axis-angle rotation method, also called the arbitrary axis rotation is derived here, and is linked with the matrix form of it:Math World: Rotation Formula. It may be what you''re using already. If so, it''s not the method, you just have to test debug it. A thread near this one by capn_midnight,
Arbitrary Axis 3D Rotation
may be useful as well.

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I guess my picture didn''t come out as I wanted.
Thanks for your help, I guess it''s just a matter
of debuggin this thing.

TT

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