Object Oriented Programming Car Example: A Beginner’s Guide to Natural Movement

Learning object-oriented programming (OOP) can be much more engaging when applied to relatable examples. Controlling a car in a program is a fantastic way to grasp fundamental OOP concepts. Let’s explore a simple car program example and see how we can make its movement more intuitive and natural.

The initial code sets up a basic car as a rectangle that can be moved and rotated using keyboard inputs. Currently, pressing ‘W’ increases the X coordinate, ‘S’ decreases it, ‘A’ increases the angle, and ‘D’ decreases the angle. This direct manipulation, while functional, isn’t very realistic for driving a car.

Below is the primitive code structure that forms the base of our car program.

1. Car car;
2. void setup(){
3. size(400,400);
4. car = new Car();
5. }
6. void draw(){
7. background(200,210,200);
8. //DRAW THE SHAPE
9. car.display();
10.
11. //CONTROL THE CAR WITH KEYBOARD (W,S,D,A)
12. if(keyPressed) {
13. if (key == 'w' || key == 'W') {
14. car.forward();
15. }
16. }
17.
18. if(keyPressed) {
19. if (key == 's' || key == 'S') {
20. car.backward();
21. }
22. }
23.
24. if(keyPressed) {
25. if (key == 'a' || key == 'A') {
26. car.left();
27. }
28. }
29.
30. if(keyPressed) {
31. if (key == 'd' || key == 'D') {
32. car.right();
33. }
34. }
35. }

1. class Car{
2. float speed, posX, posY, w, h, angle;
3. Car(){
4. posX = width/2;
5. posY = width/2;
6. w = 30;
7. h = 10;
8. speed = 5;
9. angle = radians(90);
10. }
11.
12. void display(){
13. rectMode(CENTER);
14. translate(posX, posY);
15. rotate(angle);
16. rect(0, 0, w, h);
17. }
18.
19. void forward(){
20. posX += 5;
21. }
22.
23. void backward(){
24. posX -= 5;
25. }
26.
27. void left(){
28. angle += radians(15);
29. }
30.
31. void right(){
32. angle -= radians(15);
33. }
34. }

Understanding the Car Class in OOP

This code snippet effectively demonstrates the basics of object-oriented programming by creating a Car class.

• Class Definition: class Car{ ... } defines a blueprint for creating car objects.
• Attributes (Properties): Inside the class, float speed, posX, posY, w, h, angle; declare variables that describe the car’s properties such as speed, position (posX, posY), width (w), height (h), and angle of rotation.
• Constructor: Car(){ ... } is a special method that initializes a new Car object when it’s created. It sets default values for position, size, speed, and initial angle.
• Methods (Behaviors): Functions like display(), forward(), backward(), left(), and right() define what a Car object can do. display() handles drawing the car, while the movement methods currently alter the car’s posX, posY, and angle directly.

Making Car Movement More Natural

The goal is to control the car more naturally, similar to driving in reality. Instead of directly changing X and Y coordinates with ‘W’ and ‘S’, we want ‘W’ to always move the car forward in its current facing direction, and ‘S’ to move it backward. ‘A’ and ‘D’ should handle rotation, making the car turn left and right respectively.

To achieve this “natural” movement, we need to consider the car’s angle. When we want to move forward, the change in posX and posY should be calculated based on the current angle. Trigonometry comes in handy here.

• Forward/Backward Movement: Instead of posX += 5; for forward, we need to calculate the change in X and Y using cos() and sin() of the angle. For instance, moving forward could involve increasing posX by cos(angle) * speed and decreasing posY by sin(angle) * speed (adjusting signs based on coordinate system). Backward would be the opposite.
• Rotation: The current left() and right() methods are already rotating the car by changing the angle, which is a good starting point. We can refine the rotation speed or method if needed.

By implementing these changes, pressing ‘W’ will propel the car forward in whatever direction it’s currently pointed, and ‘S’ will move it backward, relative to its orientation. ‘A’ and ‘D’ will steer the car by rotating it. This will provide a much more intuitive and “natural” driving experience for our little rectangular car.

Next Steps: Physics and Game-Like Controls

To further enhance the realism and make the car controls even more engaging, we can incorporate concepts like:

• Inertia: The car shouldn’t stop instantly when the forward key is released. It should gradually slow down, simulating inertia.
• Acceleration: Instead of instantly reaching full speed, the car should accelerate over time when ‘W’ is pressed.
• Collision Detection: To prevent the car from going off-screen or interacting with other objects, collision detection is essential.
• Gravity (if needed): For more complex simulations, especially in a 3D environment, gravity might become relevant.

These concepts are fundamental in game programming and physics simulations. To delve deeper into these areas and object-oriented programming for game development, exploring resources on game physics and OOP design patterns would be beneficial. Books and online tutorials focusing on game development with OOP principles will provide valuable guidance and expand your knowledge in creating more sophisticated and realistic simulations.