/// <summary>
/// Returns the array of collision cells that a scene node should be checked against.
/// </summary>
/// <param name="node">Scene node object.</param>
/// <returns>Array of collision cells.</returns>
private CollisionCell[] getCellsToCheck(SceneNode node)
{
// Collision cells that should be checked against
CollisionCell[] cellsToCheck = new CollisionCell[9];
int currentCellIndex = 0;
for (int i = -1; i < 2; i++)
{
for (int j = -1; j < 2; j++)
{
cellsToCheck[currentCellIndex] = null;
// Check X index bounds
int cellXIndex = collisionGrid.GetCellAtPosition(node.Position).XIndex + i;
if (cellXIndex >= 0 && cellXIndex < collisionGrid.Cells.GetLength(0))
{
// Check Y index bounds
int cellYIndex = collisionGrid.GetCellAtPosition(node.Position).YIndex + j;
if (cellYIndex >= 0 && cellYIndex < collisionGrid.Cells.GetLength(1))
{
cellsToCheck[currentCellIndex] = collisionGrid.Cells[cellXIndex, cellYIndex];
}
}
currentCellIndex++;
}
}
return(cellsToCheck);
}
/// <summary>
/// Default constructor.
/// </summary>
/// <param name="sceneDimensions">Dimensions (in pixels) of the scene.</param>
/// <param name="gridDimensions">Dimensions (in cells) of the collision grid.</param>
public CollisionGrid(Dimensions2 sceneDimensions, Dimensions2 gridDimensions)
{
cells = new CollisionCell[gridDimensions.X, gridDimensions.Y];
cellDimensions = new Dimensions2(sceneDimensions.X / gridDimensions.X,
sceneDimensions.Y / gridDimensions.Y);
for (int i = 0; i < gridDimensions.X; i++)
{
for (int j = 0; j < gridDimensions.Y; j++)
{
cells[i, j] = new CollisionCell(i, j);
}
}
}
/// <summary>
/// Update method called every game frame.
/// </summary>
/// <param name="gameTime">Snapshot of timing values.</param>
public void Update(GameTime gameTime)
{
tileMap.Update(gameTime);
foreach (SceneNode node in sceneNodeDictionary.Values)
{
if (node is Entity)
{
Entity entity = node as Entity;
prevEntityPositions[entity.Name] = entity.Position;
}
node.Update(gameTime);
handleNodeCollisions(node);
// Check if the collision cell should be changed
if (!node.IsStatic)
{
CollisionCell newCell = collisionGrid.GetCellAtPosition(node.Position);
if (newCell != node.CollisionCell)
{
// Remove scene node from old cell and add to new
node.CollisionCell.SceneNodeList.Remove(node);
newCell.SceneNodeList.Add(node);
node.CollisionCell = newCell;
node.CollisionCellsToCheck = getCellsToCheck(node);
}
// Clamp position to scene bounds
node.ClampToSceneBounds(nodeMaxBounds);
}
}
// Update scene position
position = -sceneNodeDictionary["Player"].Position;
position += positionOffset;
position.X = MathHelper.Clamp(position.X, positionMinBounds.X, positionMaxBounds.X);
position.Y = MathHelper.Clamp(position.Y, positionMinBounds.Y, positionMaxBounds.Y);
}
/// <summary>
/// Creates a collision grid for the scene.
/// </summary>
/// <param name="gridDimensions">Dimensions (in cells) of the collision grid.</param>
public void CreateCollisionGrid(Dimensions2 gridDimensions)
{
Dimensions2 sceneDimensions = tileMap.Dimensions * tileMap.TileDimensions;
collisionGrid = new CollisionGrid(sceneDimensions, gridDimensions);
// Add tiles to the proper collision grid cell
foreach (Tile tile in tileMap.TileArray)
{
collisionGrid.GetCellAtPosition(tile.Position).TileList.Add(tile);
}
// Add scene nodes to the proper collision grid cell
foreach (SceneNode node in sceneNodeDictionary.Values)
{
CollisionCell cell = collisionGrid.GetCellAtPosition(node.Position);
cell.SceneNodeList.Add(node);
node.CollisionCell = cell;
node.CollisionCellsToCheck = getCellsToCheck(node);
}
}
