16_exercises.md

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16. Classes and Structs

• Exercise 160
• Exercise 161

Exercise 160

Simple class

1. Create an empty class named Clyde within the .hpp file.
2. Look at other ghost .hpp files and see how they define the class. It does not need to inherit from the Ghost base class and it does not need any functions.

Solution

Clyde.hpp

#pragma once

#include "Ghost.hpp"

namespace pacman {

class Clyde {

};

} // namespace pacman

Clyde.cpp

#include "Clyde.hpp"

namespace pacman {

} // namespace pacman

Exercise 161

Add Clyde as a Ghost

Background: Clyde

We have three ghosts within the project. Blinky , Inky and Pinky. But Clyde is missing. Implement Clyde and their behavior.

Clyde chases PacMan, so you need to know where PacMan is currently located. But Clyde gets scared and runs back to its scatter target when PacMan gets too close (less than 8 the size of a cell). Clyde also has the scatter and eyes behaviors as the other ghosts.

Exercise

1. Clyde should inherit from Ghost
2. Make simple implementations of the functions to make it compile
3. Clyde should start at Position { .x = 15.5, .y = 14 }
4. Modify Canvas.cpp to make sure Clyde is rendered. Otherwise, it will not appear on screen.
5. Clyde's scatter target is { .x = 0, .y = 30 }
6. Clyde always targets its scatter target, unless PacMan is further than 8 tiles away
7. Update GameState.cpp with calls to the functions in Clyde to make Clyde move.

Hint Canvas.cpp and GameState.hpp

Add a line to Canvas::render to make sure that Clyde is rendered. This requires a change to GameState.hpp also.

Solution: Canvas.cpp

Canvas.cpp

  // Call renderGhost with clyde
  renderGhost(gameState.clyde);

Solution: GameState.hpp

GameState.hpp

  // Create a Clyde object in GameState together with the other ghosts
  Clyde clyde;

Solution: Clyde.hpp

Clyde.hpp

#pragma once

#include "Ghost.hpp"

namespace pacman {

class Clyde final : public Ghost {
public:
  Clyde();
  void setTarget(Position pacManPos);

protected:
  double speed() const override;
  Position initialPosition() const override;

private:
  Position scatterTarget() const;
  static constexpr Position initial_position = { 15.5, 14 };
  static constexpr Position scatter_target = { 0, 30 };
};

} // namespace pacman

Solution: Clyde.cpp

Clyde.cpp

#include "Clyde.hpp"

namespace pacman {

Clyde::Clyde()
  : Ghost(Atlas::Ghost::clyde, initial_position) {}

double Clyde::speed() const {
  if (state == State::Eyes)
    return 2;
  if (state == State::Frightened)
    return 0.5;
  return 0.75;
}

void Clyde::setTarget(Position pacManPos) {
  if (state == State::Eyes) {
    target = initialPosition();
    return;
  }

  if (isInPen()) {
    target = penDoorPosition();
    return;
  }

  // Clyde always target its scatter target, unless pacman is further than 8 tiles away
  target = scatterTarget();
  if (state == State::Scatter) {
    return;
  }

  const auto distanceFomPacMan = std::hypot(pos.x - pacManPos.x, pos.y - pacManPos.y);
  if (distanceFomPacMan > 8) {
    target = pacManPos;
  }
}

Position Clyde::initialPosition() const {
  return initial_position;
}

Position Clyde::scatterTarget() const {
  return scatter_target;
}

} // namespace pacman

Hint GameState.cpp

Search for the other ghosts in the file and add similar calls for Clyde.

Solution: GameState.cpp

GameState.cpp

  // In GameState::step
  clyde.setTarget(pacMan.position());
  clyde.update(delta);

  // In GameState::step
  checkCollision(clyde);

  // In GameState::handleDeathAnimation
  clyde.reset();

  // In GameState::eatPellets
  clyde.frighten();