protected override void UpdatePosition()
{
var potentialX = X + _changeX;
var potentialY = Y + _changeY;
var trajectory = GetTrajectory(potentialX, potentialY);
// Apply collision logic to tiles
var intersecting = from tile in CurrentLevel.CurrentScreen.Tiles
from wall in tile.Boundary
let intersection = Geometry.GetIntersection(trajectory, wall)
where intersection != null
let distance = Geometry.GetDistance(new Point(potentialX, potentialY), intersection)
orderby distance
select new { Tile = tile, Wall = wall, intersection, distance };
var closest = intersecting.FirstOrDefault();
if (closest != null)
{
var wall = closest.Wall;
var tile = closest.Tile;
if (Math.Abs(wall.X1 - wall.X2) < FloatTolerance) // vertical wall
{
if (X < wall.X1 && tile.Boundary.All(w => w.X1 >= wall.X1 && w.X2 >= wall.X1)) // ball --> wall
{
X = wall.X1 - BallRadius;
}
else if (tile.Boundary.All(w => w.X1 <= wall.X1 && w.X2 <= wall.X1)) // wall <-- ball
{
X = wall.X1 + BallRadius;
}
_changeX = 0;
_collisionX = true;
_collisionY = false;
}
else if (Math.Abs(wall.Y1 - wall.Y2) < FloatTolerance) // horizontal wall
{
if (Y < wall.Y1 && tile.Boundary.All(w => w.Y1 >= wall.Y1 && w.Y2 >= wall.Y1)) // ball ^^ wall
{
Y = wall.Y1 - BallRadius;
}
else if (tile.Boundary.All(w => w.Y1 <= wall.Y1 && w.Y2 <= wall.Y1))
{
Y = wall.Y1 + BallRadius;
}
_changeY = 0;
_collisionX = false;
_collisionY = true;
}
else // diagonal wall
{
if (wall.Y1 > wall.Y2) // diagonal \
{
if (tile.Boundary.All(w => w.X1 <= wall.X2 && w.X2 <= wall.X2)) // bottom-left filled in
{
X += BallRadius;
Y += BallRadius;
}
else // top-right filled in
{
X -= BallRadius;
Y -= BallRadius;
}
}
else if (wall.Y1 < wall.Y2) // diagonal /
{
if (tile.Boundary.All(w => w.X1 <= wall.X1 && w.X2 <= wall.X1)) // top-left filled in
{
X += BallRadius;
Y -= BallRadius;
}
else // bottom-right filled in
{
X -= BallRadius;
Y += BallRadius;
}
}
_changeX = 0;
_changeY = 0;
_collisionX = true;
_collisionY = true;
}
}
else
{
_collisionX = false;
_collisionY = false;
}
// If no collision, move ball normally
if (!_collisionX)
{
X = potentialX;
}
if (!_collisionY)
{
Y = potentialY;
}
else
{
_changeX /= Friction;
}
// Apply gravity
if (Math.Abs(_changeY) > 1 || Y < CurrentLevel.ScreenHeight - BallRadius)
{
_changeY -= _gravity;
}
// If edge of screen hit, switch screens and continue
Side?side = null;
Line boundary = null;
if (Y >= CurrentLevel.ScreenHeight)
{
side = Side.Top;
boundary = new Line(0, CurrentLevel.ScreenHeight, CurrentLevel.ScreenWidth, CurrentLevel.ScreenHeight);
}
else if (Y <= 0)
{
side = Side.Bottom;
boundary = new Line(0, 0, CurrentLevel.ScreenWidth, 0);
}
else if (X >= CurrentLevel.ScreenWidth)
{
side = Side.Right;
boundary = new Line(CurrentLevel.ScreenWidth, 0, CurrentLevel.ScreenWidth, CurrentLevel.ScreenHeight);
}
else if (X <= 0)
{
side = Side.Left;
boundary = new Line(0, 0, 0, CurrentLevel.ScreenHeight);
}
if (side.HasValue)
{
var intersection = Geometry.GetIntersection(trajectory, boundary);
CurrentLevel.MoveBallToScreen(side.Value);
CurrentLevel.InitialisePlayerPosition(side.Value, intersection, this);
}
}