private void RemoveFromCell(T obj, int xIdx, int yIdx)
{
UGridRow row = rows[yIdx];
T elt = row.cells[xIdx];
T prevElt = null;
while (elt.ID != obj.ID)
{
prevElt = elt;
elt = (T)elt.NextElt;
if (elt == null)
{
throw new Exception("Element not found");
}
}
if (prevElt == null)
{
row.cells[xIdx] = (T)elt.NextElt;
}
else
{
prevElt.NextElt = elt.NextElt;
}
--row.eltCount;
}
private void InsertToCell(T obj, int xIdx, int yIdx)
{
UGridRow row = rows[yIdx];
obj.NextElt = row.cells[xIdx];
row.cells[xIdx] = obj;
++row.eltCount;
}
/// <summary>
/// Moves an element in the grid from the former position to the new one.
/// </summary>
/// <param name="obj">The object to move</param>
/// <param name="fromX">The current position of the object in the grid</param>
/// <param name="fromY">The current position of the object in the grid</param>
/// <param name="toX">The new position of the object in the grid</param>
/// <param name="toY">The new position of the object in the grid</param>
public void Move(T obj, float fromX, float fromY, float toX, float toY)
{
int oldCol = GridLocalToCellCol(fromX);
int oldRow = GridLocalToCellRow(fromY);
int newCol = GridLocalToCellCol(toX);
int newRow = GridLocalToCellRow(toY);
UGridRow row = rows[oldRow];
if (oldCol != newCol || oldRow != newRow)
{
RemoveFromCell(obj, oldCol, oldRow);
InsertToCell(obj, newCol, newRow);
}
}
// Returns all the element IDs that intersect the specified rectangle excluding
// elements with the specified ID to omit.
public List <T> Query(float lft, float btm, float rgt, float top, int omitEltID = int.MinValue)
{
// expand the query by the size of the elements
// since we use the bottom left point to represent elements, we expand
// the bottom left of the query to catch any elements with an origin
// outside the query but with a bounding box inside it
lft -= _eltWidth;
btm -= _eltHeight;
// Find the cells that intersect the search query.
int minX = GridLocalToCellCol(lft);
int minY = GridLocalToCellRow(btm);
int maxX = GridLocalToCellCol(rgt);
int maxY = GridLocalToCellRow(top);
AABB query = new AABB(lft, top, rgt, btm);
_queryResults.Clear();
for (int y = minY; y <= maxY; ++y)
{
UGridRow row = rows[y];
if (row.eltCount == 0)
{
continue;
}
for (int x = minX; x <= maxX; ++x)
{
T elt = row.cells[x];
while (elt != null)
{
if (PointInRect(elt, in query) && elt.ID != omitEltID)
{
_queryResults.Add(elt);
}
elt = (T)elt.NextElt;
}
}
}
return(_queryResults);
}
// Returns a new grid storing elements that have a uniform upper-bound size. Because
// all elements are treated uniformly-sized for the sake of search queries, each one
// can be stored as a single point in the grid.
public UGrid(int eWidth, int eHeight, float cWidth, float cHeight,
int gridWidth, int gridHeight)
{
_numRows = (int)(gridHeight / cHeight) + 1;
_numCols = (int)(gridWidth / cWidth) + 1;
_eltWidth = eWidth;
_eltHeight = eHeight;
_invCellWidth = 1 / cWidth;
_invCellHeight = 1 / cHeight;
_width = gridWidth;
_height = gridHeight;
rows = new UGridRow[_numRows];
for (int i = 0; i < _numRows; i++)
{
rows[i] = new UGridRow();
rows[i].cells = new T[_numCols];
}
}
/// <summary>
/// Calls <see cref="IUniformGridVisitor.Grid(float, float, float, float)"/> with the grid data
/// Then traverses the whole grid and calls <see cref="IUniformGridVisitor.Cell(IUGridElt, int, int, float, float)"/>
/// on any non-empty cells.
/// </summary>
public void Traverse(IUniformGridVisitor visitor)
{
visitor.Grid(_width, _height, 1f / _invCellWidth, 1f / _invCellHeight);
for (int y = 0; y < _numRows; ++y)
{
UGridRow row = rows[y];
if (row.eltCount == 0)
{
continue;
}
for (int x = 0; x < _numCols; ++x)
{
if (row.cells[x] != null)
{
visitor.Cell(row.cells[x], x, y, 1f / _invCellWidth, 1f / _invCellHeight);
}
}
}
}
