opengl 空心圆

以下是使用OpenGL绘制空心圆的代码示例：

#include <GL/glut.h>

void display() {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);
    glBegin(GL_LINE_LOOP);
    for (int i = 0; i < 360; i++) {
        float theta = i * 3.1415926 / 180;
        glVertex2f(0.5*cos(theta), 0.5*sin(theta));
    }
    glEnd();
    glFlush();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(400, 400);    glutInitWindowPosition(100, 100);
    glutCreateWindow("OpenGL");
    glutDisplayFunc(display);
    glutMainLoop();
    return 0;
}