CODEWITHSUNDEEP
c++directxphysicsgame-physics
user
user

Reputation: 301

Bouncing ball issue

I am currently working on the 2D Bouncing ball physics that bounces the ball up and down. The physics behaviour works fine but at the end the velocity keep +3 then 0 non-stop even the ball has stopped bouncing. How should I modify the code to fix this issue?

Here is the video shows how it works. Note: Bandicam cannot record the velocity transition between -3 and 0. So, it just shows -3 when the ball stops bouncing.
https://www.youtube.com/watch?v=SEH5V6FBbYA&feature=youtu.be

Here is the generated report: https://www.dropbox.com/s/4dkt0sgmrgw8pqi/report.txt

    ballPos         = D3DXVECTOR2( 50, 100 );
    velocity        = 0;
    acceleration    = 3.0f;
    isBallUp        = false;

void GameClass::Update()
{
    // v = u + at
    velocity += acceleration;

    // update ball position
    ballPos.y += velocity;

    // If the ball touches the ground
    if ( ballPos.y >= 590 )
    {
        // Bounce the ball
        ballPos.y = 590;
        velocity *= -1;
    }

    // Graphics Rendering
    m_Graphics.BeginFrame();
    ComposeFrame();
    m_Graphics.EndFrame();
}

Upvotes: 0

Views: 1149

Answers (2)

user
user

Reputation: 301

Put a isBounce flag to make the velocity to zero when the ball stops bouncing. 

 void GameClass::Update()
{
    if ( isBounce )
    {
        // v = u + at
        velocity += acceleration;

        // update ball position
        ballPos.y += velocity;
    }
    else
    {
        velocity = 0;
    }

    // If the ball touches the ground
    if ( ballPos.y >= 590 )
    {
        if ( isBounce )
        {
            // Bounce the ball
            ballPos.y = 590;
           velocity *= -1;
        }


        if ( velocity == 0 )
        {
            isBounce = false;
        }
}

Upvotes: 0

Nico Schertler
Nico Schertler

Reputation: 32627

Accelerate only if the ball does not lie on the ground:

if(ballPos.y < 590)
    velocity += accelaration;

Btw, you should not set the ball position to 590 if you detect a collision. Instead, turn back the time to the moment when the ball hit the ground, invert the velocity and fast forward the amount of time you stepped back.

if ( ballPos.y >= 590 )
{
    auto time = (ballPos.y - 590) / velocity;
    //turn back the time
    ballPos.y = 590;
    //ball hits the ground
    velocity *= -1;
    //fast forward the time
    ballPos.y += velocity * time;
}

Upvotes: 0

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