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

[Bill Broadley]

Bill Kendrick wrote:
> On Wed, Apr 01, 2009 at 10:37:37AM -0700, Harold Lee wrote:
>>    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.
> 
> Neat idea, but I worry about kitchensinkness. :)
> 
> -bill!
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How about doing it like xfig, it's really simple just 3 clicks, lets you do
any kind of arc as you want, I can try it out on my 4 year old if ya want.

If you use xfig to demonstrate click on grid so you can use the same P1/P2
spacing with multiple curves.  If P1 is lower and P2 is higher how do you
decide on a radius that draws 1/4th of a circle (your first example), or more
than a 1/4th and get a curve that goes above the higher point (as in your 3rd).