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Re: Creating a circle in a data structure

by Crackers2 (Parson)
 on May 28, 2007 at 07:21 UTC Need Help??

in reply to Creating a circle in a data structure

Instead of going round the circle, it may be easier to iterate over all values in one direction, i.e. something like:

```foreach \$ydist ( 0..\$radius ) {
# using the formula:

# Take advantage of symmetry to plot 4 points at once
# (for circle outline)
\$circle{\$x_center-\$xdist}{\$y_center-\$ydist}++;
\$circle{\$x_center+\$xdist}{\$y_center-\$ydist}++;
\$circle{\$x_center-\$xdist}{\$y_center+\$ydist}++;
\$circle{\$x_center+\$xdist}{\$y_center+\$ydist}++;

# Or to fill up the whole disc...
foreach \$x ( \$x_center-\$xdist .. \$x_center+\$xdist ) {
\$circle{\$x}{\$y_center-\$ydist}++;
\$circle{\$x}{\$y_center+\$ydist}++;
}
}

Of course this assumes you're dealing with a grid of integers. Right now it also counts every point on the axis twice but that's easy enough to fix.

Replies are listed 'Best First'.
Re^2: Creating a circle in a data structure
by Skeeve (Parson) on May 28, 2007 at 08:08 UTC
You can omit the square root if you compare to the square of the radius. I think one will get a big speed improvement from this.

s\$\$([},&%#}/&/]+}%&{})*;#\$&&s&&\$^X.(\$'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`\$''`"e
Re^2: Creating a circle in a data structure
by AK108 (Friar) on May 28, 2007 at 20:17 UTC
When using the whole disc, it works nicely. The individual points do not work, unfortunately.

I can use the whole disc method, but I need to be able to calculate the distance from the center of the circle. I've tried many formulas, and some look close (working for x values or y values), but nothing actually works.

Yes you're right. To complete the outline you have to connect each point to the previous point. Something like this:

```\$prevdist = 0;

foreach \$ydist ( 0..\$radius ) {
# using the formula:

# Take advantage of symmetry to plot 4 lines at once
# (for circle outline, draw a line from the previous
# point to the new one)
foreach \$xdist (\$prevdist..\$newxdist) {
\$circle{\$x_center-\$xdist}{\$y_center-\$ydist}++;
\$circle{\$x_center+\$xdist}{\$y_center-\$ydist}++;
\$circle{\$x_center-\$xdist}{\$y_center+\$ydist}++;
\$circle{\$x_center+\$xdist}{\$y_center+\$ydist}++;
}

\$prevdist = \$newxdist;
}

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