Hello,

I am wanting to make a pong clone to test my new knowledge with Java and slick. i haven't started anything yet but im planning it out. I am just a it confused on how you get the direction the ball goes after you hit it with the paddle. I don't know anything about physics (im taking it in school though). do i just randomly generate a direction or is there some stupid long mathematical equation thanks for any help.

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#2
Members - Reputation: **121**

Posted 20 August 2012 - 05:28 AM

That doesn't sound good regardless of how much I spin it around in my head."stupid long mathematical equation"

Anyway, you could just go with some simple conditional statements and inverse the direction of the ball. If you want something more complex you'd have to do some vector maths with at least the ball's direction vector, the paddle's forward vector and the position the ball hit the paddle.

[source lang="cpp"] // edge of playing field if (pong.ball.centre_y > 0.6f) { pong.ball_velocity_y = -ball_speed; } else if (pong.ball.centre_y < -0.6f) { pong.ball_velocity_y = ball_speed; } // ball hit a paddle on the right side if (pong.ball_velocity_x > 0 && collides(&pong.ball, &pong.bats[1]) ) { pong.ball_velocity_x = -pong.ball_velocity_x; } // ball hit a paddle on the left side if (pong.ball_velocity_x < 0 && collides(&pong.ball, &pong.bats[0]) ) { pong.ball_velocity_x = -pong.ball_velocity_x; }[/source]

**Edited by Tudor Nita, 20 August 2012 - 06:09 AM.**

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#4
Crossbones+ - Reputation: **11967**

Posted 20 August 2012 - 06:07 AM

A simple model for a ball bouncing off a paddle (ignoring edge effects) is perfect reflection. If you use vectors, it has an elegant expression not at all complicated once you know some vector algebra. Note that if your paddle is perfectly vertical, this is equivalent to negating the x-component of the ball's velocity, so you could start by doing that instead and improve later on (perhaps by adding round edges).

*“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”*