/// <summary>
/// Find a valid spawn point in the world.
/// </summary>
/// <param name="radius">The radius of the object to be spawned.</param>
/// <param name="random">A persistent Random object.</param>
/// <returns>The spawn point.</returns>
public static Vector2 FindSpawnPoint(GameplayObject spawnedObject, float radius)
{
// safety-check the singleton
if (collisionManager == null)
{
throw new InvalidOperationException(
"The collision manager has not yet been initialized.");
}
// safety-check the parameters
if ((radius < 0f) || (radius > Dimensions.Width / 2))
{
throw new ArgumentOutOfRangeException("radius");
}
// keep trying to find a valid point
Vector2 spawnPoint = new Vector2(
radius + Dimensions.X +
RandomMath.Random.Next((int)Math.Floor(Dimensions.Width - radius)),
radius + Dimensions.Y +
RandomMath.Random.Next((int)Math.Floor(Dimensions.Height - radius)));
for (int i = 0; i < findSpawnPointAttempts; i++)
{
bool valid = true;
// check the barriers
if (Barriers != null)
{
CollisionMath.CircleLineCollisionResult result =
new CollisionMath.CircleLineCollisionResult();
foreach (Rectangle rectangle in Barriers)
{
if (CollisionMath.CircleRectangleCollide(spawnPoint, radius,
rectangle, ref result))
{
valid = false;
break;
}
}
}
// check the other objects
if (valid)
{
foreach (GameplayObject gameplayObject in collisionManager)
{
if (!gameplayObject.Active || (gameplayObject == spawnedObject))
{
continue;
}
if (CollisionMath.CircleCircleIntersect(spawnPoint, radius,
gameplayObject.Position, gameplayObject.Radius))
{
valid = false;
break;
}
}
}
if (valid)
{
break;
}
spawnPoint = new Vector2(
radius + Dimensions.X + RandomMath.Random.Next(
(int)Math.Floor(Dimensions.Width - radius)),
radius + Dimensions.Y + RandomMath.Random.Next(
(int)Math.Floor(Dimensions.Height - radius)));
}
return(spawnPoint);
}
/// <summary>
/// Update the collision system.
/// </summary>
/// <param name="elapsedTime">The amount of elapsed time, in seconds.</param>
public static void Update(float elapsedTime)
{
// safety-check the singleton
if (collisionManager == null)
{
throw new InvalidOperationException(
"The collision manager has not yet been initialized.");
}
// move each object
for (int i = 0; i < collisionManager.Count; ++i)
{
if (collisionManager[i].Active)
{
// determine how far they are going to move
Vector2 movement = collisionManager[i].Velocity * elapsedTime;
// only allow collisionManager that have not collided yet
// collisionManager frame to collide
// -- otherwise, objects can "double-hit" and trade their momentum
if (collisionManager[i].CollidedThisFrame == false)
{
movement = MoveAndCollide(collisionManager[i], movement);
}
// determine the new position
collisionManager[i].Position += movement;
// collide with the barriers
for (int b = 0; b < collisionManager.barriers.Count; ++b)
{
CollisionMath.CircleLineCollisionResult result =
new CollisionMath.CircleLineCollisionResult();
if (collisionManager[i] is Projectile)
{
CollisionMath.CircleRectangleCollide(
collisionManager[i].Position - movement,
collisionManager[i].Radius,
collisionManager.barriers[b], ref result);
if (result.Collision)
{
collisionManager[i].Position -= movement;
collisionManager[i].Die(null, false);
}
}
else
{
CollisionMath.CircleRectangleCollide(
collisionManager[i].Position,
collisionManager[i].Radius,
collisionManager.barriers[b], ref result);
if (result.Collision)
{
// if a non-projectile hits a barrier, bounce slightly
float vn = Vector2.Dot(collisionManager[i].Velocity,
result.Normal);
collisionManager[i].Velocity -= (2.0f * vn) *
result.Normal;
collisionManager[i].Position += result.Normal *
result.Distance;
}
}
}
}
}
CollisionManager.Collection.ApplyPendingRemovals();
}