WEBVTT 00:00.120 --> 00:01.830 Hello again! In this video, 00:01.830 --> 00:06.540 we are going to look at how to make our bouncing ball bounce off the edges of the window. 00:08.310 --> 00:11.280 To do this, we need to be able to find the position of the ball. 00:11.640 --> 00:14.780 So we are going to add a member function which will return that. 00:15.810 --> 00:21.900 We are also going to add some member functions which will come in useful, later on. So we can find the centre 00:21.900 --> 00:25.140 of the ball, and also the bounding rectangle. 00:26.220 --> 00:31.320 The bounding rectangle is actually the same as the texture rectangle, but it has different significance. 00:31.950 --> 00:33.390 With a texture rectangle. 00:33.400 --> 00:34.770 we are interested in the image 00:34.770 --> 00:37.560 that it is bound to. With a bounding rectangle, 00:37.980 --> 00:39.720 we are interested in its geometry. 00:41.520 --> 00:46.530 When we get the bounding rectangle, we will get the coordinates of the origin. 00:47.430 --> 00:53.880 And then, if we want the centre, we can just add half the width of the rectangle to move across, and 00:53.880 --> 00:56.400 then we move down by half the height of the rectangle. 00:58.690 --> 01:02.410 These functions are going to be useful for all the sprites, not just the bull. 01:03.010 --> 01:07.480 SFML has some functions for detecting collisions which use the bounding rectangle. 01:07.750 --> 01:09.490 So that is why we are interested in it. 01:10.150 --> 01:13.420 And we are going to use that with bricks, which are not a moving entity. 01:13.870 --> 01:16.750 So we are going to add this to the basic entity class. 01:18.900 --> 01:24.330 So here is our revised entity class. We have added these member functions. 01:25.970 --> 01:29.100 We are going to make these noexcept and const, for efficiency. 01:29.490 --> 01:32.100 I hope you are noticing these C++11 features! 01:32.460 --> 01:38.310 So noexcept for functions which cannot throw, constexpr for expressions which are constant 01:38.310 --> 01:38.940 expressions. 01:39.660 --> 01:44.430 And when we override a virtual function, we use the "override" keyword. 01:47.480 --> 01:50.210 get_bounding_box() will return the bounding rectangle. 01:50.600 --> 01:57.380 This will be an object of type FloatRect. get_centre() will return the centre of the sprite, as 01:57.380 --> 02:02.900 a Vector2f, which we have met before, and then we have functions for getting the x and y coordinates. 02:05.130 --> 02:09.240 I have added a source file for implementing these member functions. 02:10.050 --> 02:12.360 get_bounding_box() will call the member 02:12.360 --> 02:15.300 function of the sprite, get_global_bounds(). 02:15.750 --> 02:22.170 This will return the bounding rectangle in global coordinates, which means the coordinates relative 02:22.230 --> 02:24.030 to the top left hand corner of the window. 02:24.660 --> 02:27.030 So that is the same coordinates as the display. 02:29.190 --> 02:30.030 get_centre(). 02:30.030 --> 02:38.490 This will return in the coordinates of the sprite. So the center of the sprite will be half the bounding 02:38.490 --> 02:44.790 box width from the top left hand corner, and half the box height below the top left hand corner. 02:48.620 --> 02:53.930 And then, to get to the position, we just call get_position() on the sprite. That returns a Vector2f, 02:54.290 --> 02:58.520 and then we use the 'x' and 'y' members for the coordinates of the position. 03:02.120 --> 03:06.230 In the ball class, we need to modify the update() function. 03:06.740 --> 03:10.730 So if the ball is moving off the screen, we need to make sure it moves back onto the screen. 03:12.170 --> 03:18.110 If it is moving off the screen to the left, x is less than zero. Then that means the velocity is negative. 03:18.110 --> 03:21.080 It is moving to the left and we want it to move to the right. 03:21.380 --> 03:23.600 So we need to make the velocity positive. 03:24.140 --> 03:26.300 So we just change the sign of the velocity. 03:27.980 --> 03:32.720 If it is moving off the right hand side of the screen, x is greater than the width of the window. 03:33.320 --> 03:38.420 Then we want to make it move to the left, so we make the velocity negative. 03:40.280 --> 03:44.570 And similarly for the top and bottom of the screen. At the top y equals zero. 03:44.960 --> 03:48.320 So we invert the velocity to make it move down, instead of up. 03:49.070 --> 03:53.930 And when y is equal to the window height at the bottom of the screen, then we change the sign again. 03:54.200 --> 03:56.330 So it is now moving up instead of down. 03:57.590 --> 03:59.900 And we do not need to change anything else in the code. 04:00.140 --> 04:04.040 We do not need to change the main() function, because this is all done in the ball class. 04:07.020 --> 04:11.070 And then when we run it, you can see the ball is now bouncing off the edge of the screen. 04:11.580 --> 04:12.330 That is much better. 04:13.230 --> 04:14.490 Okay, that is it for this video. 04:14.940 --> 04:15.780 I will see you next time. 04:15.780 --> 04:18.090 But until then, keep coding!