2D胶囊体与2D圆是否相交，算法来源于《游戏开发中的数学与物理》一书

CapsuleHitCircle.cs

/// <summary>
/// 2D胶囊体与2D圆是否相交
/// </summary>
/// <param name="capsulePoint">胶囊体的圆心</param>
/// <param name="capsuleDir">胶囊体的向量</param>
/// <param name="capsuleRadius">胶囊体的半径</param>
/// <param name="circlePoint">圆心的位置</param>
/// <param name="circleRadius">圆的半径</param>
/// <returns></returns>
private static bool CapsuleAndCircleCheckHit(Vector2 capsulePoint, Vector2 capsuleDir, float capsuleRadius, Vector2 circlePoint, float circleRadius)
{
    var dx = circlePoint.x - capsulePoint.x;
    var dy = circlePoint.y - capsulePoint.y;
    var t = (capsuleDir.x * dx + capsuleDir.y * dy) /
            (capsuleDir.x * capsuleDir.x + capsuleDir.y * capsuleDir.y);
    t = Mathf.Clamp01(t);

    var mx = capsuleDir.x * t + capsulePoint.x;
    var my = capsuleDir.y * t + capsulePoint.y;

    var disSqrt = (mx - circlePoint.x) * (mx - circlePoint.x) +
                    (my - circlePoint.y) * (my - circlePoint.y);

    var radiusSum = capsuleRadius + circleRadius;
    if (disSqrt <= radiusSum * radiusSum)
    {
        return true;
    }

    return false;
}