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So we figured out how to detect 

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collision with the top and bottom walls and make our ball bounce off the walls.

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The next thing we need to do is to detect when there's a collision with the

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paddle and make the ball bounce off the paddle.

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This is probably going to be the hardest part of this program yet

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so I wanna talk you through the logic. Now,

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how can we know when the ball has hit the paddle? Now,

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normally we use the distance method to check what is the distance between the

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ball and the paddle. And if it's less than a certain amount,

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then we can be relatively sure that they've made contact with each other.

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So the code that we normally use would be something like this.

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We get our ball and we check its distance from the paddle.

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Now remember that our ball has a width of 20 pixels and our paddle has a

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width of 20 pixels. Normally we would say, well,

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if that distance between the two of them is less than 20, well,

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then they've probably made contact, right?

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But the problem occurs when the ball hits the paddle, not right in the center,

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but at the edge of the paddle,

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because this distance measures the center of the ball from the centre of the

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paddle as the distance.

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So you can see that this distance is way bigger than 20,

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so it's not going to register as a collision.

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How can we solve this problem? Well,

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we could add on an additional condition. We could check well

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if the ball has gone past a certain point on the X-axis,

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if it's gone far enough over to the right and it's within a 50 pixel distance of

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the paddle,

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then that also means it's made contact with the paddle. Inside our main.py

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I'm going to add a comment to detect collision with right paddle.

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So let's experiment with some numbers here and see if we can get the ball to

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bounce off the paddle. In this case,

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we're going to check if the ball.distance to the r_paddle is less than

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50 and the ball.xcor is greater than 340.

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If the ball has hit the right paddle,

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let's print something to the console to test our code. Let's print made contact.

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So if we run this code and I manage to make contact with the ball,

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you can see that it says 'Made contact' in our console.

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So instead of just printing made contact,

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what we want the ball to do is to again, to bounce. Now,

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this bounce is a little bit different from the last bounce,

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because the previous one was changing its Y coordinate so that it moved in the

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opposite along the vertical. But in this case,

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we actually want it to move along the opposite direction in the horizontal

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because the paddle is here and the ball is coming this way,

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we want it to go back this way. So instead of just calling this bounce,

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I'm going to right-click on it and then refactor and rename to bounce_

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y because this is bouncing in the Y-axis. Now,

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once we hit refactor, it'll change it here and it will change it here.

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Now on top of that, I'm going to define my bounce_x,

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so it bouncing in the X-axis, and this is very similar.

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We're going to change the x_move,

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so the amount that the ball moves each time when the move method is called and

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I'm going to multiply it by -1,

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so reversing the X direction.

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And then when our collision is detected,

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we're going to get the ball to bounce in the X direction.

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So now if we run our code,

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you can see that even though this only works on the right paddle,

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when the ball hits the right paddle

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it moves back and it bounces back towards the left.

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It changes the direction that it was moving in the X-axis.

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So now lets add the collision for both paddles because they both need to bounce

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in the X-axis

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and so we're going to tag onto this a 'or' statement and we're going to say

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or if the ball.distance to the left paddle is also less than 50

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and on top of that

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the ball.xcor is less than -340.

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So this basically checks to see if the ball has gone far enough to the left as

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to be past the paddle and its within a distance of 50 pixels from the left

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paddle. So if we run the code right now,

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you can see that not only does our ball bounce when it hits the right.

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So now when we run the program again,

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you can see that not only does the ball bounce on the right paddle,

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it also bounces when it hits the left paddle.

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Now there's a little bit more tweaking that we can do with the coordinates because

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you can see that when the ball hits the paddle,

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it goes a little bit too far before it actually reverses direction.

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So we can change this to a slightly smaller number if we want it to bounce

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before it's within the actual paddle.

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So we can change this to 320 and this one also to 320 and notice what

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happens now. Before it hits the actual paddle,

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it now actually bounces and it doesn't look like as if the ball's fallen into the

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paddle before it turns back. And there you have it.

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Now we just have to figure out what should happen when the paddle misses the

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ball. For all of that and more, I'll see you in the next lesson.