While details of what you need to implement for this project are in the C++ files, here is a copy in case you need it. The main project page can be found here.

Overview of Classes

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You will be modifying the following classes:

• Point represents a 2D point on the screen¹.

• Velocity represents a 2D vector that indicates the direction and speed of movement.

• Ball represents the bouncing ball. It has a circle shape and thus can be located by a Point that represents its center and an integer that represents its radius. We also need to associate a Velocity to the ball since it can move freely in the game world.

• Paddle represents the paddle that the player controls. It has a rectangle shape and thus can be represented by a Point for the location of its upper-left corner and a pair (w, h) for its width and height. The paddle is also movable but can only do so horizontally, so it is sufficient to represent its velocity with a single integer.

• Brick represents a brick that the player has to destroy. Like the paddle, it also has a rectangle shape so we represent it in the same way, but without a velocity.

• World represents the entire game world. It is a rectangle area with (0,0) as its top-left corner and (w, h) as its lower-right corner, where w and h are its width and height. This rectangle defines the area of the entire coordinate system that is visible to the player.

Functions to Implement

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Complete the member functions listed below. The code you write in this section is going to serve as base utilities for the next section.

• Ball

  • Implement the constructor of the Ball class. The constructor takes three parameters: the center point of the ball, the radius of the ball, and the velocity of the ball.

  • Implement the getCenter(), getRadius(), and getVelocity() member functions, which returns the center point, the radius, and the velocity of the ball, respectively.

• Paddle

  • Implement the constructor of the Paddle class. The constructor takes three parameters: the upper-left corner of the paddle, the width of the paddle, the height of the paddle, and the velocity of the paddle.

  • Implement the getUpperLeft() and getLowerRight() member functions, which returns the upper-left corner and the lower-right corner of the paddle, respectively.

• Brick

  • A brick is like a paddle without velocity. Implement its constructor, getUpperLeft() and getLowerRight() member functions similarly to the Paddle class.

• World

  • Implement the World constructor. There are 5 parameters in the constructor: its width, its height, a ball, a paddle, and a vector of bricks.

  • Implement the get() functions for each of the 5 parameters.

World::isLegal()

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Users of the World class are able to use the class’ constructor to create arbitrary game world, including worlds that contain an illegal game states. For example, there is nothing that prevents the user from constructing a world without any bricks, or a world with a ball of velocity zero. The isLegal() member function should detect such illegal initial game states. Specifically, it does the following check:

• There should be at least one brick in the world.

• The ball must have a nonzero velocity.

• All entities (ball, paddle, and bricks) must locate completely inside the boundaries of the world.

• Entities must not collide with one another.²

World::update()

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Given a legal World object, the final task is to write the update logic for the game: World::update(). The function takes the user input as a parameter, which is an scoped enum that has three possibilities: Input::None (player does not press any key), Input::Left (player wants to move the paddle to the left), Input::Right (player wants to move the paddle to the right). Based on the user input, it should update the internal state of the World object:

1. First, the paddle moves. If the original location of the paddle is (x, y), the new location would be (x + v, y), where v is the paddle’s velocity. However, if the paddle would move beyond the left (or right) boundary of the game world, you need to keep it inside the world and align it to the left (or right, respectively) world boundary.

2. Next, the paddle’s velocity changes according to the user input.

   • If the input is Input::None, set the velocity to zero.

   • If the input is Input::Left, set the velocity to -Paddle::DefaultVelocity.

   • If the input is Input::Right, set the velocity to Paddle::DefaultVelocity.

3. Then, the ball moves. If the original location of the ball is (x, y), the new location would be (x + v_x, y + v_y), where v_x and v_y are the ball’s horizontal velocity and vertical velocity, respectively.

   After this step, it is OK if the ball moves to an illegal position (e.g. it goes outside of the game world, or it overlaps with either the paddle or some bricks). In the next step, we will fix that by changing the ball’s velocity in such a way that will move the ball out of the illegal position in the next couple of frames.

4. Next, the ball’s velocity changes.

   • If the ball collides with or goes beyond the left boundary of the world, set its horizontal velocity to Ball::DefaultHorizontalVelocity.

   • If the ball collides with or goes beyond the right boundary of the world, set its horizontal velocity to -Ball::DefaultHorizontalVelocity.

   • If the ball collides with or goes beyond the upper boundary of the world, set its vertical velocity to Ball::DefaultVerticalVelocity.

   • If the ball collides with the paddle, set its vertical velocity to -Ball::DefaultVerticalVelocity.

   • If the ball collides with or goes beyond the lower boundary of the world, the game is over. We handle this case by throwing an exception: throw GameOverException();³

• Finally, remove all bricks that collide with the ball.