I''m sitting here at my computer, listening to White Zombie at 1:00 in the morning, and a problem has found its way into my brain. I know how to determine Circle-Segment collision, and I even know how to determine when and where a Circle-Circle collision occurs (which we can call time-based collision). Unfortunately, I don''t know how to determine when a Circle-Segment collision occurs for a given delta-time. I''ve sought articles that explain this, to no avail. The Circle-segment collision formula looks like this: c = center of circle n = nearest point from c to segment a, b = ends of segment A = segment in question B = segment between a and c C = segment between b and c . = dot product n = a + [(b - a) * (B . A)] / [(B . A) + (C . A)] Since I''m using time-based collision in my project, I need to determine when and where a collision occurs for a given delta-time (the period between screen updates). Any help on this matter is greatly appreciated. Thanks in advance.