WEBVTT 00:00.060 --> 00:00.630 Hello again! 00:00.930 --> 00:05.310 In this video, we are going to look at how to make our paddle move across the bottom of the screen. 00:07.660 --> 00:09.820 So let's try and specify what we want. 00:10.390 --> 00:16.780 When the user presses the left arrow key, the paddle will move to the left, when the screen is next updated. 00:17.650 --> 00:22.270 And if the user presses the right arrow key, the paddle will move to the right. 00:23.110 --> 00:26.170 If the user presses any other key, we just ignore it. 00:26.920 --> 00:29.680 And this is only for left or right movement. 00:30.760 --> 00:33.010 The paddle is not going to move up or down. 00:35.120 --> 00:38.210 The obvious place to make these changes is in the update() 00:38.500 --> 00:43.850 member function of the paddle class, because that determines how the paddle will appear, the next time that the 00:43.850 --> 00:45.050 frame is displayed. 00:45.890 --> 00:50.770 So in this function, we are going to check for the key press, and then we are going to set the "x" member 00:50.960 --> 00:54.350 of the velocity, to make the paddle move left or right. 00:55.370 --> 00:58.520 And in fact, I think you could actually do this yourselves. 00:59.060 --> 01:04.340 There is code in the main() function, which shows how to check for a key press. If you go to the SFML 01:04.550 --> 01:10.220 website and look through the documentation, you should be able to find which keys correspond to the 01:10.580 --> 01:15.410 left and right arrow keys. And then you can make your changes in the update() member function. 01:15.950 --> 01:20.320 So I will let you pause the video, if you are intending to do that. 01:25.070 --> 01:29.330 I have added another constant, which is going to be the paddle speed. 01:29.840 --> 01:33.740 So the paddle will move 8 pixels between updates, when it is moving. 01:36.470 --> 01:41.450 I have actually added a new member function, to respond to the input from the player. 01:42.140 --> 01:44.830 This is a private member function of the class. 01:45.680 --> 01:52.580 You could argue that this is something which could be useful for any moving entity. So it should perhaps 01:52.580 --> 01:57.560 be a protected member function of the moving entity_class. In this game, 01:58.220 --> 02:03.410 the paddle is going to be the only thing which responds to keyboard input, so it makes sense to have 02:03.410 --> 02:04.460 it as a private member. 02:05.090 --> 02:09.620 If we are watching a different game where different entities can respond to key put input, 02:09.980 --> 02:11.930 then perhaps we could organize the code differently. 02:15.830 --> 02:22.700 I have also made one other small change, which is to change the origin of the sprite. By default, 02:22.790 --> 02:25.820 this will be the top left hand corner of the bounding rectangle. 02:26.510 --> 02:29.540 I find it easier to think in terms of the centre of the sprite. 02:30.170 --> 02:31.910 So I have made this change. 02:32.510 --> 02:36.410 But if you do not like that, you can just ignore that, or remove it from your code. 02:38.930 --> 02:45.860 And then in the update() member function, I just call this new member function, which will deal with keyboard input. 02:48.250 --> 02:49.750 The draw() function is the same. 02:50.470 --> 02:52.120 And then here is this 02:52.120 --> 02:53.650 process_player_input() member function. 02:56.010 --> 03:03.750 We start by checking for the left elbow. And then if, it has been pressed, we set the "x" member of the 03:03.900 --> 03:06.960 velocity to be minus the paddle speed. 03:07.590 --> 03:12.270 So that is going to move 8 pixels to the left, the next time the display is updated. 03:13.710 --> 03:20.460 If the user presses the right key, then we set the "x" member to be plus 8 pixels. 03:21.930 --> 03:27.840 We also need to check that we have not reached the edge of the window. With the ball, 03:27.840 --> 03:31.090 we made the ball bounce off when it reached the edge. With the paddle, 03:31.120 --> 03:32.250 we do not want to do that. 03:32.610 --> 03:38.190 Instead, the paddle is just going to stop. So it will sit there and wait, until the user presses the 03:38.190 --> 03:39.750 key to make it go in the other direction. 03:40.170 --> 03:45.630 So if we reach the left hand edge of the screen, then the paddle will stop until the user presses the 03:45.660 --> 03:46.430 right arrow. 03:48.380 --> 03:52.430 And if there is no key press, then we just set the velocity to be zero. 03:56.740 --> 03:59.560 And now, if I press the left key, it moves to the left. 04:00.280 --> 04:02.470 If I press the right key, it moves to the right. 04:03.310 --> 04:06.610 If I hold the left key, it keeps on going until it reaches the edge. 04:07.840 --> 04:13.630 And then for the right. I am actually using the centre, so the paddle can go halfway into the edge. 04:14.530 --> 04:19.660 The reason for that is, there are some variations, where the way that the ball bounces depends on which 04:19.660 --> 04:20.950 part of the pebble it hits. 04:21.820 --> 04:23.350 Okay, that is it for this video. 04:23.770 --> 04:24.610 I will see you next time. 04:24.610 --> 04:26.860 But until then, keep coding!