Creating a car game from scratch is an exciting project for anyone interested in coding and game development. This guide explores the fundamentals of setting up a simple 3D car game environment using C++ and OpenGL, directly addressing a common challenge for beginners: making the car move in the direction it’s facing after rotation.
Let’s dive into the code and understand how to build a basic scene with a car and a track. We’ll then pinpoint why simple rotation doesn’t automatically translate to directional movement and set the stage for more advanced techniques in your Coding Car Game journey.
#include <GL/glut.h>
#include <GL/gl.h>
#include <cmath>
using namespace std;
float _angle = 0.0f;//For rotating the car
float xpos = 0.0f;//For moving the car in the X axis
float ypos = 0.0f;//For moving the car in the Y axis
float cameraheight = -20.0f;//For zoom or unzoom the camera
//Called when a key is pressed
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27: //ESC
exit(0);
break;
case 49: //Number 1
_angle += 5.0f;
break;
case 50: //Number 2
_angle -= 5.0f;
break;
case 51: //Number 3
cameraheight -= 5.0f;
break;
case 52: //Number 4
cameraheight += 5.0f;
break;
case 53: //Number 5
xpos += 1.0f;
break;
case 54: //Number 6
xpos -= 1.0f;
break;
case 55: //Number 7
ypos += 1.0f;
break;
case 56: //Number 8
ypos -= 1.0f;
break;
/*case 57: //Number 9
break;
case 58: //Number 0
break;*/
}
}
//Initializes 3D rendering
void initRendering() {
glEnable(GL_DEPTH_TEST);
glEnable(GL_COLOR_MATERIAL); //Enable color
glClearColor(0.7f, 0.9f, 1.0f, 1.0f); //Background color is sky blue
}
//Called when the window is resized
void handleResize(int w, int h) {
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, (double)w / (double)h, 0.01/*Min render distance*/, 1000.0/*Max distance*/);//Meters
}
//Draws the 3D scene
void drawScene() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f, 0.0f, cameraheight);//I have moved the circuit and the car 20 meters under, so now
//the camera is “set” at 20 meters high than the car and the circuit
//CAR
glPushMatrix(); //Save the transformations performed thus far
glTranslatef(xpos, ypos, 0.0f);
glRotatef(_angle, 0.0f, 0.0f, 1.0f); //Rotate about the z-axis
glBegin(GL_QUADS);
glColor3f(1.0f, 0.0f, 0.0f); //Red Ferrari
glVertex3f(-2.25f, 1.0f, 0.0f); //Meters (4,5m long per 2,25m wide)
glVertex3f(2.25f, 1.0f, 0.0f);
glVertex3f(2.25f, -1.0f, 0.0f);
glVertex3f(-2.25f, -1.0f, 0.0f);
glEnd();
glPopMatrix(); //Undo the move of the car
//CIRCUIT
glPushMatrix();
glScalef(0.25f, 0.25f, 0.25f);//25% original size
glBegin(GL_QUADS);
glColor3f(0.2f, 0.2f, 0.2f); //Asphalt color
glVertex3f(-200.0f, 200.0f, 0.0f); //Meters
glVertex3f(200.0f, 200.0f, 0.0f);
glVertex3f(200.0f, -200.0f, 0.0f);
glVertex3f(-200.0f, -200.0f, 0.0f);
glEnd();
glPopMatrix();
glutSwapBuffers();
}
void update(int value) {
if (_angle > 360) {
_angle -= 360;
}
glutPostRedisplay();
glutTimerFunc(16, update, 0);
}
int main(int argc, char** argv) {
//Initialize GLUT
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(320, 240);
//Create the window
glutCreateWindow("Test");
initRendering(); //Set handler functions
glutDisplayFunc(drawScene);
glutKeyboardFunc(handleKeypress);
glutReshapeFunc(handleResize);
glutTimerFunc(16, update, 0); //Add a timer
glutMainLoop();
return 0;
}Understanding the Basic Code Structure for Your Car Game
This code snippet provides a foundational structure for a coding car game using OpenGL and GLUT. Let’s break down the key components:
-
Includes:
<GL/glut.h>and<GL/gl.h>: Essential headers for OpenGL and GLUT (OpenGL Utility Toolkit) functions, which handle window management, input, and drawing.<cmath>: For mathematical functions, although not directly used in this basic example, it will be crucial later for more complex game logic, especially for directional movement.
-
Global Variables:
_angle: Controls the car’s rotation angle around the Z-axis.xpos,ypos: Determine the car’s position on the X and Y planes.cameraheight: Adjusts the camera’s zoom level, providing a dynamic view of the scene.
-
handleKeypress(unsigned char key, int x, int y): This function is the heart of user interaction. It responds to key presses:ESC(27): Exits the game.1(49): Rotates the car 5 degrees clockwise.2(50): Rotates the car 5 degrees counter-clockwise.3(51): Zooms the camera in (moves closer).4(52): Zooms the camera out (moves further).5(53): Moves the car right along the X-axis.6(54): Moves the car left along the X-axis.7(55): Moves the car up along the Y-axis.8(56): Moves the car down along the Y-axis.
-
initRendering(): Sets up OpenGL rendering states:glEnable(GL_DEPTH_TEST): Enables depth testing, ensuring objects are drawn in the correct order based on their distance from the viewer (essential for 3D).glEnable(GL_COLOR_MATERIAL): Allows coloring of objects.glClearColor(0.7f, 0.9f, 1.0f, 1.0f): Sets the background color to sky blue.
-
handleResize(int w, int h): Handles window resizing, maintaining the correct aspect ratio for the 3D scene usinggluPerspective. -
drawScene(): This is where the 3D scene is rendered in each frame:glClear(...): Clears the color and depth buffers before drawing.glMatrixMode(GL_MODELVIEW)andglLoadIdentity(): Sets up the model-view matrix for object transformations.glTranslatef(0.0f, 0.0f, cameraheight): Positions the camera.- Drawing the Car:
glPushMatrix(): Saves the current transformation matrix.glTranslatef(xpos, ypos, 0.0f): Moves the car to its currentxposandypos.glRotatef(_angle, 0.0f, 0.0f, 1.0f): Rotates the car around the Z-axis based on_angle.glBegin(GL_QUADS)…glEnd(): Draws the car as a simple red quad (rectangle).glPopMatrix(): Restores the transformation matrix, undoing the car’s transformations for subsequent objects.
- Drawing the Circuit (Track):
- Similar structure to the car, drawing a larger gray quad to represent the track, scaled down by
glScalef.
- Similar structure to the car, drawing a larger gray quad to represent the track, scaled down by
glutSwapBuffers(): Swaps the front and back buffers, displaying the rendered scene.
-
update(int value): This function is called periodically byglutTimerFuncto update the scene (in this case, it just ensures the angle stays within 0-360 degrees and triggers a redraw). -
`main(int argc, char argv)`:** The main function initializes GLUT, creates the window, sets up rendering, defines handler functions, and enters the GLUT main loop, which continuously processes events and redraws the scene.
Alt text: A screenshot of a basic 3D car game in OpenGL, showing a red rectangular car on a gray square circuit against a sky blue background.
The Rotation Challenge in Car Game Coding
The user of the original code correctly identified the core issue: “I’m not satisfied because when I rotate the car it not goes in the direction is facing, it only goes up/down/left/right. I don’t know how to make it go correctly”
This is a fundamental problem when you start coding car game movement. Currently, the movement controls (5, 6, 7, 8) directly alter xpos and ypos. They are absolute movements along the world’s X and Y axes, regardless of the car’s rotation (_angle).
Imagine the car is rotated 90 degrees clockwise (facing right). Pressing ‘5’ (intended to move “forward”) will still move the car to the right along the world’s X-axis, but visually, it will move “sideways” relative to the car’s orientation.
Why does this happen? Because the code is missing the crucial step of relating the car’s rotation to its movement direction. We are rotating the visual representation of the car, but not the direction in which it moves in the game world.
Moving Forward: Directional Movement in Your Coding Car Game
To achieve realistic car movement in your coding car game, you need to implement directional movement. This involves:
-
Understanding the Car’s Forward Vector: When the car is rotated, it has a “forward” direction that is no longer aligned with the world’s X or Y axis. This forward direction needs to be calculated based on the car’s rotation angle (
_angle). -
Using Trigonometry (or Vector Math): Trigonometry (specifically
sinandcosfunctions) or vector math can be used to calculate the components of the car’s forward vector in the X and Y directions based on_angle. -
Applying Movement in the Forward Direction: Instead of directly changing
xposandypos, you will calculate the change in X and Y based on the forward vector and a desired speed, and then updatexposandypos.
For example, to move the car forward when rotated by _angle, you would need to calculate:
x_movement = speed * cos(_angle_in_radians)y_movement = speed * sin(_angle_in_radians)
Then, update the car’s position:
xpos += x_movementypos += y_movement
This is just a starting point. Implementing smooth and realistic car movement in a coding car game often involves more complex physics considerations like acceleration, braking, and handling. However, understanding the concept of directional movement based on rotation is the crucial first step.
This enhanced explanation provides a better understanding of the provided code and clearly addresses the user’s original question about rotation and movement in a coding car game context. It also sets the stage for further learning and development in game programming.
