internal void Add(ref Int2 index, Grid2DEntry entry)
{
int cellIndex;
int sortingHash;
if (TryGetIndex(ref index, out cellIndex, out sortingHash))
{
cells.Elements[cellIndex].Add(entry);
return;
}
GridCell2D cell = cellPool.Take();
cell.Initialize(ref index, sortingHash);
cell.Add(entry);
cells.Insert(cellIndex, cell);
count++;
}
internal void Remove(ref Int2 index, Grid2DEntry entry)
{
int cellIndex;
int sortingHash;
if (TryGetIndex(ref index, out cellIndex, out sortingHash))
{
cells.Elements[cellIndex].Remove(entry);
if (cells.Elements[cellIndex].entries.Count == 0)
{
//The cell is now empty. Give it back to the pool.
GridCell2D toRemove = cells.Elements[cellIndex];
//There's no cleanup to do on the grid cell.
//Its list is empty, and the rest is just value types.
cells.RemoveAt(cellIndex);
cellPool.GiveBack(toRemove);
count--;
}
}
}
internal void UpdateOverlaps(Grid2DSortAndSweep owner)
{
//Sort along x axis using insertion sort; the list will be nearly sorted, so very few swaps are necessary.
for (int i = 1; i < entries.Count; i++)
{
Grid2DEntry entry = entries.Elements[i];
for (int j = i - 1; j >= 0; j--)
{
if (entry.item.boundingBox.Min.X < entries.Elements[j].item.boundingBox.Min.X)
{
entries.Elements[j + 1] = entries.Elements[j];
entries.Elements[j] = entry;
}
else
{
break;
}
}
}
//Sweep the list looking for overlaps.
for (int i = 0; i < entries.Count; i++)
{
Grid2DEntry a = entries.Elements[i];
Grid2DEntry b;
//TODO: Microoptimize
for (int j = i + 1;
j < entries.Count && a.item.boundingBox.Max.X >= (b = entries.Elements[j]).item.boundingBox.Min.X;
j++)
{
if (!(a.item.boundingBox.Min.Y > b.item.boundingBox.Max.Y ||
a.item.boundingBox.Max.Y < b.item.boundingBox.Min.Y ||
a.item.boundingBox.Min.Z > b.item.boundingBox.Max.Z ||
a.item.boundingBox.Max.Z < b.item.boundingBox.Min.Z))
{
//Now we know this pair is overlapping, but we do not know if this overlap is already added.
//Rather than use a hashset or other heavy structure to check, rely on the rules of the grid.
//It's possible to avoid adding pairs entirely unless we are the designated 'responsible' cell.
//All other cells will defer to the cell 'responsible' for a pair.
//A simple rule for determining the cell which is responsible is to choose the cell which is the
//smallest index in the shared cells. So first, compute that cell's index.
Int2 minimumSharedIndex = a.previousMin;
if (minimumSharedIndex.Y < b.previousMin.Y)
{
minimumSharedIndex.Y = b.previousMin.Y;
}
if (minimumSharedIndex.Y > b.previousMax.Y)
{
minimumSharedIndex.Y = b.previousMax.Y;
}
if (minimumSharedIndex.Z < b.previousMin.Z)
{
minimumSharedIndex.Z = b.previousMin.Z;
}
if (minimumSharedIndex.Z > b.previousMax.Z)
{
minimumSharedIndex.Z = b.previousMax.Z;
}
//Is our cell the minimum cell?
if (minimumSharedIndex.Y == cellIndex.Y && minimumSharedIndex.Z == cellIndex.Z)
{
owner.TryToAddOverlap(a.item, b.item);
}
}
}
}
}
internal void Remove(Grid2DEntry entry)
{
entries.Remove(entry);
}
internal void Add(Grid2DEntry entry)
{
//binary search for the approximately correct location. This helps prevent large first-frame sort times.
entries.Insert(GetIndex(entry.item.boundingBox.Min.X), entry);
}