Caleb C. Cannon

My old boss, David Bobzien is running for Nevada Assembly in district 24. He’s put up a campaign weblog and information page. District 24 is north of I-80 between McCarran Blvd. and 395 and includes the University and the Keystone/Kings Row area. Further north District 24 continues into Stead between Stead Blvd. and Military Rd. Dave is a great guy and I wish him the best of luck with his campaign.

I’ve been playing around with “metaballs” today. Metaballs are a type of isosurface that can be thought of as an equipotential surface created by a set of point charges. Another way to think of them is as contour maps of mountains surrounded by water. Mathematically it’s a graph of a scalar potential function taken below (or above) some cutoff. e.g. the scalar potential from E&M:

Φ(r)= k e ∑ i=1 n q i | r− r i |When animated (ie. the mountains can move their heights add together) the effect is reminiscent of a lava lamp or an oil slick in water. Typically the way metaballs are rendered is by dividing the region of interest into small elements (typically the size of a pixel or voxel) and running a test on each element to determine if the region intersects with the equipotential surface. For example:

for x = 0 to screen_width
{
for y = 0 to screen_height
{
potential = 0
for i = 0 to num_balls
{
x2 = (meta_ball[i].x - x)^2
y2 = (meta_ball[i].y - y)^2
potential += meta_ball[i].charge / sqrt(x2 + y2)
}
if (potential < max_potential and potential > min_potential)
DrawPixel(x,y,color)
}
}