Circle-Rectangle collision detection (intersection)

Question

How can I tell whether a circle and a rectangle intersect in 2D Euclidean space? (i.e. classic 2D geometry)

Answer 1

Here's a fast one-line test for this:

if (length(max(abs(center - rect_mid) - rect_halves, 0)) <= radius ) {
  // They intersect.
}

This is the axis-aligned case where rect_halves is a positive vector pointing from the rectangle middle to a corner. The expression inside length() is a delta vector from center to a closest point in the rectangle. This works in any dimension.