[vox-tech] [OT] Math question: help me make a rainbow

[Bill Kendrick]

On Tue, Mar 31, 2009 at 07:43:19PM -0700, Jeff Newmiller wrote:
> You seem to be trying to implement an algorithm that needs
> three points with only two inputs... you are bound to fail.
> One method I have seen is to click-drag-release to get the
> two endpoints and then interactively pick up the mouse position
> to track the height of the arc until a second click finishes
> the input. You would have to back out the actual radius of
> the circle if you needed it, but two inputs don't magically
> become three.

I think that third point is the center of the circle, based on
the normal off the vector between P1,P2, where it intersects
the segment (x1,(max(y1,y2))) and (x2,(max(y1,y2)))

maybe? ;)

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-bill!
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