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

[Harold Lee]

Not sure if the formulas you've set out do this, but couldn't the rainbow
tool treat the difference between y coordinates as depth, the way that the
grass tool does? When y1 == y2, you get a semi-circle with the height == 1/2
* abs(x2 - x1), i.e. the radius. Otherwise you get a rainbow with a wider
base at the point closer to the bottom of the screen that arcs back to the
other point.

On Tue, Mar 31, 2009 at 10:12 PM, Bill Broadley <bill at cse.ucdavis.edu>wrote:

> Bill Kendrick wrote:
> > On Tue, Mar 31, 2009 at 07:21:36PM -0700, Bill Broadley wrote:
> >> Some.  Not sure what you are getting at though.  You want to draw 180
> degrees
> >> of a circle with the end points defined by p1 and p2?  What if you want
> to
> >> make an upside down rainbow?  Or 1/2 of one?
> >
> > I only want to draw all 180 degress if y1==y2.  Otherwise, it'd be
> > less of the arc.  (See my ASCII diagrams)
>
> Hrm, I don't think ascii is going to help, at least for me.  Ah, ok, I have
> an
> idea of what you think you want to do.  I think you do need 3 points.  A
> center, radius, range of angles.  Basically there are an infinite number of
> 180 degree curves that go through 2 points, and there's no way to know how
> high the peak should be, nor which exact fraction of a circle to display.
>
> So for your diagrams how do you decide that in case 1 you do 1/2 a circle
> and
> the circle doesn't go above P2, but in case #3 you get 60% of a circle.
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