Silverlight Circular Collision Animation

posted by joel on 05.14.08 @ 12:34 pm in Microsoft, Silverlight

Building on the sample I created on Circular Motion, in this example I add a concept of collision.  In physics, deflection is the event that occurs where an object collides and bounces off of another surface.  In my example, two spheres collide at a given X/Y causing each ball to reverse direction and maintains its current speed and angle.

Just as in my previous example I use a single DispatcherTimer and a generic collection of UserConrols. To keep track of the direction that each ball is traveling I added a boolean property to my “Ball” user control to determine if it was rotating clockwise.

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void _timer_Tick(object sender, EventArgs e)
{
    foreach (Ball ball in _balls)
    {
        double x = 0.0
        double y = 0.0
        double angle = ball.Rotate.Angle
 
        CalculatePosition(ball.Clockwise, ref x, ref y, ref angle, 1)
        //update the position of the ball
        ball.Rotate.Angle = angle
        ball.Translate.X = x
        ball.Translate.Y = y
 
        //check to see if a collision has occured
        if (ball.CollisionType == Ball.CollisionTypes.Deflect)
        {
            foreach (Ball ball2 in _balls)
            {
                if (!ball.Equals(ball2))
                {
                    double b2X = 0.0
                    double b2Y = 0.0
                    double b2A = ball2.Rotate.Angle
                    //if we wait until the two balls are at the same X/Y then the balls
                    //will have overlapped.  Instead, predict by looking 5 degrees ahead 
                    //then switching direction.
                    CalculatePosition(ball2.Clockwise, ref b2X, ref b2Y, ref b2A, 5)
                    if (Math.Ceiling(x).Equals(Math.Ceiling(b2X))
                        &amp&amp Math.Ceiling(y).Equals(Math.Ceiling(b2Y)))
                    {
                        ball.Clockwise = !ball.Clockwise
                        ball2.Clockwise = !ball2.Clockwise
                        //ball.sound.Position = TimeSpan.FromMilliseconds(0)
                        //ball.sound.Play()
                        break
                    }
                }
            }
        }
    }
}

As you can see in the code above, I am doing a quick check to see if my rotating ball is defined to deflect upon collision. In this example, this is the only type of collision supported. In the future, I might add things like exploding on impact or magnetism upon the collision.

The first step in the circular rotation is to move each ball to its new X/Y position. Once moved, I check to see if any other balls overlap its current X/Y location. To make the collision more realistic (no overlap), I predict where each additional ball will exist 5 degrees forward of its current angle. This allows me to simulate the ball just touching each other before reversing directions.

Code: CircularCollision.zip


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1 Comment so far >>

[...] Silverlight Circular Collision Animation - another physics based silverlight animation from Joel. Step-by-step explanation of the example and source code is available. [...]

By Silverlight articles and demos wrap-up for the last 3 days on 05.16.08 7:00 am

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