private void CheckBallBricksCollision(Ball ball, GameTime gameTime)
{
for (int i = 0; i < bricks.Length; i++)
{
for (int j = 0; j < bricks[i].Length; j++)
{
if (bricks[i][j] != null && IsOpenForHit(i, j))
{
if (!bricks[i][j].IsDestroyed)
{
Brick brick = bricks[i][j];
CollisionResolutionInfo collisionInfo = CollisionUtils.CheckCollision(gameTime.ElapsedGameTime.Milliseconds, ball, brick);
if (collisionInfo != null)
{
HitBrick(i, j, ball.IsFlaming, bricks[i][j].IsDetonating, 0);
ball.Velocity = collisionInfo.BallVelocity;
ball.DrawRectangle = collisionInfo.BallDrawRectangle;
}
}
}
}
}
}
/// <summary>
/// Finds a moment of ball-brick collision.
/// Change position and velocity of the ball after collision.
/// </summary>
/// <param name="timeStep">The time step.</param>
/// <param name="ball">The ball.</param>
/// <param name="brick">The brick.</param>
/// <returns>The collision resolution info object.</returns>
public static CollisionResolutionInfo CheckCollision(int timeStep, Ball ball, Brick brick)
{
BoundingBallRect initialBallRect = new BoundingBallRect();
BoundingBallRect currentBallRect = new BoundingBallRect();
if (ball.CollisionRectangle.Intersects(brick.CollisionRectangle))
{
if (!ball.IsFlaming)
{
// initialize non-changing properties
currentBallRect.drawRectangle.Width = ball.DrawRectangle.Width;
currentBallRect.drawRectangle.Height = ball.DrawRectangle.Height;
currentBallRect.collisionRectangle = ball.CollisionRectangle;
// back up ball to it's location before the time step
float dX = (ball.Velocity.X * timeStep);
float dY = (ball.Velocity.Y * timeStep);
initialBallRect.drawRectangle.X = ball.DrawRectangle.X - (int)dX;
initialBallRect.drawRectangle.Y = ball.DrawRectangle.Y - (int)dY;
initialBallRect.drawRectangle.Width = ball.DrawRectangle.Width;
initialBallRect.drawRectangle.Height = ball.DrawRectangle.Height;
initialBallRect.collisionRectangle.X = ball.CollisionRectangle.X - (int)dX;
initialBallRect.collisionRectangle.Y = ball.CollisionRectangle.Y - (int)dY;
// find a moment of the ball-brick collision
// at fixed time step of 60 fps, time increment can only be 8, 4, 2, or 1
int timeIncrement = timeStep / 2;
int collisionDt = timeStep; // we know we have a collision or we wouldn't be here
int dt = timeIncrement;
while (timeIncrement > 0)
{
// move ball forward by dt from its initial position
dX = ball.Velocity.X * dt;
dY = ball.Velocity.Y * dt;
// update ball bounding rectangle
currentBallRect.drawRectangle.X = initialBallRect.drawRectangle.X + (int)dX;
currentBallRect.drawRectangle.Y = initialBallRect.drawRectangle.Y + (int)dY;
currentBallRect.collisionRectangle.X = initialBallRect.collisionRectangle.X + (int)dX;
currentBallRect.collisionRectangle.Y = initialBallRect.collisionRectangle.Y + (int)dY;
// cut time increment in half as we search for the time of collision
timeIncrement /= 2;
if (currentBallRect.collisionRectangle.Intersects(brick.CollisionRectangle))
{
// collision detected, so save collision dt and reduce dt to make it earlier
collisionDt = dt;
dt -= timeIncrement;
}
else
{
// no collision detected, so increase dt to make it later
dt += timeIncrement;
}
}
// get rectangle location at start of collision
int collisionStartTime = collisionDt;
dX = ball.Velocity.X * collisionStartTime;
dY = ball.Velocity.Y * collisionStartTime;
currentBallRect.drawRectangle.X = initialBallRect.drawRectangle.X + (int)dX;
currentBallRect.drawRectangle.Y = initialBallRect.drawRectangle.Y + (int)dY;
currentBallRect.collisionRectangle.X = initialBallRect.collisionRectangle.X + (int)dX;
currentBallRect.collisionRectangle.Y = initialBallRect.collisionRectangle.Y + (int)dY;
// find the area where ball overlaps brick
Rectangle intersectionArea = Rectangle.Intersect(currentBallRect.collisionRectangle, brick.CollisionRectangle);
CollisionSide collisionSide = GetCollisionSide(currentBallRect.collisionRectangle,
intersectionArea, ball.Velocity);
// move objects through complete time step
int preCollisionDuration = collisionStartTime - 1;
int postCollisionDuration = timeStep - collisionStartTime + 1;
CollisionResolutionInfo cri = BounceBall(ball.Velocity, initialBallRect.drawRectangle,
preCollisionDuration, postCollisionDuration,
collisionSide);
return(cri);
}
else
{
return(new CollisionResolutionInfo(ball.Velocity, ball.DrawRectangle));
}
}
else
{
// no collision
return(null);
}
}
