球不显示 OpenGL C++

Question

我是 OpenGL 和 C++ 的新手，但我有一些 C、Java 和 Python 的背景。

我正在打乒乓球，但屏幕上没有绘制我的 Ball 对象。有什么我没看到的吗？

我的猜测是它是主要方法中的一些东西，或者只是我忽略的东西，但我在它上面花了一点时间，但似乎没有任何效果。

#include <GL/glut.h>
#include <cmath>

class GameObject
{
public:
    float xpos;
    float ypos;

    void draw() {}
    void update() {}
};

class Paddle : public GameObject
{
public:
    float xlen;
    float ylen;

    float xvel;
    float yvel;

    Paddle() {}

    Paddle(float x, float y, float xl, float yl, float xv, float yv)
    {
        xpos = x;
        ypos = y;
        xlen = xl;
        ylen = yl;
        xvel = xv;
        yvel = yv;
    }

    void draw()
    {
        glPushMatrix();
        glTranslatef(xpos, ypos, 0.0f);
        glColor3f(1.0f, 1.0f, 1.0f);
        glBegin(GL_QUADS);
        glVertex2f(-xlen, -ylen);
        glVertex2f(-xlen, ylen);
        glVertex2f(xlen, ylen);
        glVertex2f(xlen, -ylen);
        glEnd();
        glPopMatrix();
    }

    void update()
    {
        xpos += xvel;
        ypos += yvel;

        if (xpos > 1.0f || xpos < -1.0f)
        {
            xvel *= -1.0f;
        }

        if (ypos > 1.0f || ypos < -1.0f)
        {
            yvel *= -1.0f;
        }
    }
};

class Ball : public GameObject
{
public:
    float rad;

    float xvel;
    float yvel;

    Ball() {}

    Ball(float x, float y, float rad, float xv, float yv)
    {
        xpos = x;
        ypos = y;
        rad = rad;
        xvel = xv;
        yvel = yv;
    }

    void draw()
    {
        glPushMatrix();
        glTranslatef(xpos, ypos, 0.0f);
        glColor3f(1.0f, 1.0f, 1.0f);
        glBegin(GL_TRIANGLE_FAN);
        for (int i = 0; i < 360; i++)
        {
            float theta = i * 3.14159 / 180;
            glVertex2f(rad * cos(theta), rad * sin(theta));
        }
        glEnd();
        glPopMatrix();
    }

    void update()
    {
        xpos += xvel;
        ypos += yvel;

        // Check for collision with the edges of the window
        if (xpos > 1.0f || xpos < -1.0f)
        {
            xvel *= -1.0f;
        }

        if (ypos > 1.0f || ypos < -1.0f)
        {
            yvel *= -1.0f;
        }
    }
};

class Game
{
public:
    Paddle paddle1;
    Paddle paddle2;
    Ball ball;
    Game()
        : paddle1(-0.85f, 0.0f, 0.05f, 0.3f, 0.0f, 0.1f),
          paddle2(0.85f, 0.0f, 0.05f, 0.3f, 0.0f, -0.1f),
          ball(0.0f, 0.0f, 0.3f, 0.0f, 0.0f)
    {
    }
};

Game game = Game(); // global game object

void display()
{
    // Clear the screen
    glClear(GL_COLOR_BUFFER_BIT);

    // Draw the paddles
    game.paddle1.draw();
    game.paddle2.draw();

    // Draw the ball
    game.ball.draw();

    // Swap the front and back buffers (double buffering)
    glutSwapBuffers();
}

void update(int value)
{
    // Update the object's position
    game.paddle1.update();
    game.paddle2.update();

    game.ball.update();

    // Redraw the scene
    glutPostRedisplay();

    // Call update() again after 16 milliseconds (60 frames per second)
    glutTimerFunc(16, update, 0);
}

int main(int argc, char **argv)
{
    // Initialize GLUT and create the window
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE);
    glutInitWindowSize(720, 720);
    glutCreateWindow("Pong");

    // Set up the display and update callbacks
    glutDisplayFunc(display);
    glutTimerFunc(0, update, 0);

    // Start the main loop
    glutMainLoop();

    return 0;
}

我试过弄乱它，甚至给它相同的代码来绘制桨，但它不起作用。