# ball hitting paddle in breaout

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In the game breakout how am I supposed to get the new value of x and y for the ball when it hits the paddle at a certain spot?

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You can set up different bounding boxes around your paddle and depends on where the ball hit you can make you decision and position the x and y in the correct location.

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Take a point directly below (or above) the centre of the paddle. Then get the vector from this point to the point of collision (collision point - point below center). Normalize this vector and then multiply it by the ball’s previous speed (length of previous velocity – you may want to add a small number on to this so as to increase the speed with each hit). This is the balls new velocity.
That is how I might go about it. If you need more information I’ll be happy to assist.

Hope this helps,
Jackson Allan

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What does it mean to normalize a vector?

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jack_1313, I did something like this:

ball->xs = (ball->x - paddle->x2) * ball->xs;
ball->ys = ((ball->y + 21) - paddle->y) * ball->ys;

where xs = ball's horizontal velocity
ys = vertical velocity
x = current horizontal position of ball which is the collison point
y = same as x but this is the vertical position

x2 = left corner of paddle
y2 = botom of paddle

but all this does is exit out of my game loop which means it's failing right here:
if (ball->x < paddle->x1 || ball->x > paddle->x2);

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Hello again.

To normalize a vector is to make it a unit vector (length of 1.0). One can read a quick and to-the-point explanation of a 2d vector that will surely come in handy right here. Check the forum FAQ for more in-depth information.

/*paddle->x = centre of paddlepaddle->y = bottom of paddleball->xsball->ys = velocity of ballball->xball->y = ball position (presumably point of collision)*/float vx;float vy;float vl;float sl;//Get the vector from the paddle bottom centre to the point of collisionvx = ball->x – paddle->x;vy = ball->y – paddle->y;//Get the length of the vectorvl = sqrt( vx * vx + vy * vy );//Normalize this vector (make it’s length 1.0):vx *= ( 1.0f / vl );vy *= ( 1.0f / vl );//Multiply it by the length of the ball’s previous velocitysl = sqrt(ball->sx * ball->sx + ball->sy * ball->sy );vx *= sl;vy *= sl;//This is the new velocityball->sx = vx;ball->sy = vy;

That should do the trick (code untested).

Hope this helps,
Jackson Allan

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wow thanks, I made a few changes and everything works well now.

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Ooops… I forgot to mention the final part:

vx = ball->x – paddle->x;
vy = ball->y – paddle->y;

Should be changed to something more like this:

vx = ball->x – paddle->x;
vy = ball->y – ( paddle->y + 50.0f );

Or some such depending on the size of the paddles and the angle variation you want in your game. Obviously the lager the number you add to paddle->y the lesser the variation. Sounds like you’ve already figured this one out though.

Anyhow, glad to be of help,
Jackson Allan