[A89] Re: filling ellipses
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[A89] Re: filling ellipses
jeff, if this helps
The equation (((x-h)^2)/a^2) + (((y-k)^2)/b^2) = test
where (h,k) = (x,y) that you put into the draw ellipse function and the a b
respectivly will returne 0 < test < 1 (test > 0 && test < 1) if those points
are inside the ellipse. I think thats right, if it does not work let me
know and I'll get out my old math book :)
BioSLuDge
----- Original Message -----
From: "jeff" <jefromi42@yahoo.com>
To: <assembly-89@lists.ticalc.org>
Sent: Saturday, July 07, 2001 2:04 PM
Subject: [A89] filling ellipses
>
> Does anyone know a good fast way to fill an ellipse (using not only black
and white, but xor)?
> There is a draw ellipse function, but nothing for filling it. A for loop
decrementing the radius
> by one doesn't work; it leaves out a few pixels. You can't use a decimal
radius, which might
> work. I was thinking along the lines of either calculating horizontal
points on the circle then
> connecting them with a line or doing a pixel test thing, sweeping across,
filling once it detects
> the edge of the circle. The problem is, I'm not sure if this could be
efficient if you're drawing
> onto a background. Another idea was to create an array when you begin
that symbolizes the
> rectangle around the ellipse, then use ones and zeros to create the filled
circle, basically as a
> sprite in a different form, then copy it to the screen pixel by pixel.
I'm not sure that any of
> these will be very fast, though.
>
> Thanks,
> jeff
>
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