Circle line-segment collision detection algorithm?

Question

I have a line from A to B and a circle positioned at C with the radius R.

What is a good alg

Answer 1

I wrote a small script to test intersection by projecting circle's center point on to line.

vector distVector = centerPoint - projectedPoint;
if(distVector.length() < circle.radius)
{
    double distance = circle.radius - distVector.length();
    vector moveVector = distVector.normalize() * distance;
    circle.move(moveVector);
}

http://jsfiddle.net/ercang/ornh3594/1/

If you need to check the collision with the segment, you also need to consider circle center's distance to start and end points.

vector distVector = centerPoint - startPoint;
if(distVector.length() < circle.radius)
{
    double distance = circle.radius - distVector.length();
    vector moveVector = distVector.normalize() * distance;
    circle.move(moveVector);
}

https://jsfiddle.net/ercang/menp0991/