/// <summary>
/// casts a line from start to end returning the first solid tile it intersects. Note that start and end and clamped to the tilemap
/// bounds so make sure you pass in valid positions else you may get odd results!
/// </summary>
/// <param name="start">Start.</param>
/// <param name="end">End.</param>
public TiledTile linecast(Vector2 start, Vector2 end)
{
var direction = end - start;
// worldToTilePosition clamps to the tilemaps bounds so no need to worry about overlow
var startCell = tiledMap.worldToTilePosition(start);
var endCell = tiledMap.worldToTilePosition(end);
start.X /= tiledMap.tileWidth;
start.Y /= tiledMap.tileHeight;
// what tile are we on
var intX = startCell.X;
var intY = startCell.Y;
// ensure our start cell exists
if (intX < 0 || intX >= tiledMap.width || intY < 0 || intY >= tiledMap.height)
{
return(null);
}
// which way we go
var stepX = Math.Sign(direction.X);
var stepY = Math.Sign(direction.Y);
// Calculate cell boundaries. when the step is positive, the next cell is after this one meaning we add 1.
// If negative, cell is before this one in which case dont add to boundary
var boundaryX = intX + (stepX > 0 ? 1 : 0);
var boundaryY = intY + (stepY > 0 ? 1 : 0);
// determine the value of t at which the ray crosses the first vertical tile boundary. same for y/horizontal.
// The minimum of these two values will indicate how much we can travel along the ray and still remain in the current tile
// may be infinite for near vertical/horizontal rays
var tMaxX = (boundaryX - start.X) / direction.X;
var tMaxY = (boundaryY - start.Y) / direction.Y;
if (direction.X == 0f)
{
tMaxX = float.PositiveInfinity;
}
if (direction.Y == 0f)
{
tMaxY = float.PositiveInfinity;
}
// how far do we have to walk before crossing a cell from a cell boundary. may be infinite for near vertical/horizontal rays
var tDeltaX = stepX / direction.X;
var tDeltaY = stepY / direction.Y;
// start walking and returning the intersecting tiles
var tile = tiles[intX + intY * width];
if (tile != null)
{
return(tile);
}
while (intX != endCell.X || intY != endCell.Y)
{
if (tMaxX < tMaxY)
{
intX += stepX;
tMaxX += tDeltaX;
}
else
{
intY += stepY;
tMaxY += tDeltaY;
}
tile = tiles[intX + intY * width];
if (tile != null)
{
return(tile);
}
}
return(null);
}
