/// <summary>
/// Returns whether a point is inside a circle.
/// </summary>
/// <param name="point">Point to test.</param>
/// <param name="circle">Circle to test.</param>
/// <returns>Whether point is inside circle.</returns>
private static bool TestPointInCircle(
Vector2 point, CollisionMaskCircle circle
)
{
return((point - circle.Center).LengthSquared() <=
circle.Radius * circle.Radius);
}
/// <summary>
/// Tests a collision between two circles.
/// </summary>
/// <param name="circleA">First circle mask to test.</param>
/// <param name="circleB">Second circle mask to test.</param>
/// <returns>Whether the two circles intersect.</returns>
public static bool TestCollisionCircleCircle(
CollisionMaskCircle circleA, CollisionMaskCircle circleB
)
{
// Check distance between center of both circles is less
// than or equal to their combined radius.
float distanceSqr =
(circleA.Center - circleB.Center).LengthSquared();
float radiusSqr =
(circleA.Radius + circleB.Radius) *
(circleA.Radius + circleB.Radius);
return(distanceSqr <= radiusSqr);
}
/// <summary>
/// Tests a collision between a circle and line mask.
/// </summary>
/// <param name="circle">Circle mask to test.</param>
/// <param name="line">Line mask to test.</param>
/// <returns>Whether the line intersects the circle.</returns>
public static bool TestCollisionLineCircle(
CollisionMaskCircle circle, CollisionMaskLine line
)
{
// Early exit if end points of line are inside circle.
if (TestPointInCircle(line.Start, circle) ||
TestPointInCircle(line.End, circle)
)
{
return(true);
}
// Constants
float constA =
(line.End.X - line.Start.X) * (line.Start.X - line.End.X);
float constB =
(line.Start.Y - line.End.Y) * (line.End.Y - line.Start.Y);
float constC =
(line.Start.Y - line.End.Y) * (line.End.X - line.Start.X);
// Get x point
float pointX = (
constC * line.Start.Y - constC * circle.Center.Y + constA *
circle.Center.X - constB * line.Start.X) / (constA - constB);
// Only test if point is on line segment.
if (
(pointX >= line.Start.X && pointX <= line.End.X) ||
(pointX >= line.End.X && pointX <= line.Start.X)
)
{
// Create vector from point on line
Vector2 tangentLineIntersection = new Vector2(
pointX,
(line.End.Y - line.Start.Y) * (pointX - line.Start.X)
/ (line.End.X - line.Start.X) + line.Start.Y
);
// Is distance between tangent intersection and circle center
// less than radius?
float distance =
(circle.Center - tangentLineIntersection).LengthSquared();
return(distance <= circle.Radius * circle.Radius);
}
return(false);
}
/// <summary>
/// Tests for a collision with another CollisionMask.
/// </summary>
/// <param name="other">Other mask to test with.</param>
/// <returns>Returns whether the two masks are colliding.</returns>
public override bool TestCollision(CollisionMask other)
{
// Circle circle collision
if (other.GetType() == typeof(CollisionMaskCircle))
{
CollisionMaskCircle mask = (CollisionMaskCircle)other;
return(Collision.TestCollisionLineCircle(mask, this));
}
else if (other.GetType() == typeof(CollisionMaskLine))
{
throw (new NotImplementedException());
}
else
{
throw (new NotImplementedException());
}
}