mcdonald@uxe.cso.uiuc.edu (01/28/88)
I need some help doing calculations on ellipses. Note that this is for a bit-mapped graphics screen, in pixel coordinates. What I am doing is looking at spheres in 3-d space, projecting them onto the screen and drawing them. What I haven't figured out is as follows: I have three spheres. Their centers define a triangle. I want to draw in the section of the plane defined by the three centers which lies outside the (assumed opaque) spheres, as hidden by the front two spheres. I have been unable to come up with a simple(not involving trig functions) method of determining the equation of the line connecting the triangle with the surface of the sphere, which is a section of an ellipse. Has anybody solved this problem? (I need something fast, as I need to do this at least 4 times per second on an ordinary IBM-PC. Without the fillrd in triangle I am getting about six per second.) Doug McDonald (mcdonald@uiucuxe)