/// <summary>
/// Checks collisons with every object in the tree
/// against only the root of the other tree
/// </summary>
/// <param name="treeTvr">
/// The tree to narrow down (as a PCS traverser)
/// </param>
/// <param name="otherRoot">
/// The other tree to check against
/// </param>
/// <returns>A GameObject that collides with other tree, otherwise null</returns>
private GameObject NarrowDownCollisonTree(PCSTraverser treeTvr, GameObject otherRoot)
{
// Make sure the traverser starts at the root
treeTvr.StartOver();
// Loop through (almost) every object in this tree (pointed by the traverser)
while (treeTvr.IsValid())
{
GameObject current = treeTvr.GetCurrent() as GameObject;
// Check if the current object collides with the other root
if (Collider.Intersect(current.Collider, otherRoot.Collider))
{
// If the current object has children
if (treeTvr.IsThereChild())
{
// Check collisons with the children
treeTvr.NextChild();
}
// The current object is at the bottom of the
// collison hierarchy (it is a last-child node)
else
{
// A collison was found!
break;
}
}
// No collision
else
{
// Go to the next sibling
// If there are no more siblings, this loop breaks
treeTvr.NextSibling();
}
}
// Return the current object. This can be null.
return(treeTvr.GetCurrent() as GameObject);
}
//
// Methods
//
/// <summary>
/// Check all collisions
/// </summary>
public void Update()
{
// Iterate through the entire first tree...
if (this.ShouldScanEntireFirstTree)
{
// ... But only if the two roots collide
// Disclaimer: This loop only works if nothing from
// the first tree will ever be deleted. This is true
// for Aliens vs Shields (Aliens don't get deleted)
firstTvr.Reassign(this.collisionTreeRootFirst);
secondTvr.Reassign(this.collisionTreeRootSecond);
// Leave if either roots are null
if (firstTvr.IsValid() == false || secondTvr.IsValid() == false)
{
return;
}
if (Collider.Intersect(collisionTreeRootFirst.Collider, collisionTreeRootSecond.Collider))
{
this.iterator.Reassign(this.collisionTreeRootFirst);
// For every collision check allowed...
for (int i = 0; i < this.collisionChecks; i++)
{
// For every node in the first tree...
for (this.iterator.StartOver(); this.iterator.IsDone() == false; this.iterator.GetNext())
{
// Collisions must be checked against a leaf node
var currentNode = this.iterator.GetCurrent() as GameObject;
if (currentNode.Child == null)
{
// Move second tree's traverser to the root
this.secondTvr.StartOver();
// Scan the second tree against the first collidee
GameObject secondCollidee = this.NarrowDownCollisonTree(secondTvr, currentNode);
// A collision occurred
if (secondCollidee != null)
{
// If we are here, there was a collision!
this.DeclareCollision(currentNode, secondCollidee);
}
}
}
}
}
}
// Don't iterate through the entire first tree. Just narrow it down.
else
{
for (int i = 0; i < this.collisionChecks; i++)
{
firstTvr.Reassign(this.collisionTreeRootFirst);
secondTvr.Reassign(this.collisionTreeRootSecond);
// Leave if either roots are null
if (firstTvr.IsValid() == false || secondTvr.IsValid() == false)
{
return;
}
// Scan the first tree against the entire second root
GameObject firstCollidee = this.NarrowDownCollisonTree(firstTvr, this.collisionTreeRootSecond);
if (firstCollidee == null)
{
// Leave if no collison was found
return;
}
// Scan the second tree against the first collidee
GameObject secondCollidee = this.NarrowDownCollisonTree(secondTvr, firstCollidee);
if (secondCollidee == null)
{
// Leave if no collison was found
return;
}
// If we are here, there was a collision!
this.DeclareCollision(firstCollidee, secondCollidee);
}
}
}