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我写了几行代码来绘制一个旋转的矩形：

#include "glut.h"
static GLfloat spin = 0.0; /* current angle */
void init(void) 
{
    glClearColor (0.0, 0.0, 0.0, 0.0);
    glShadeModel (GL_FLAT);
}
void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glPushMatrix();
    glRotatef(spin, 0.0, 0.0, 1.0);  /* rotate Oxyz (OZ) */
    glColor3f(1.0, 1.0, 1.0); /* bgr-color: white; */
    glRectf(-25.0, -25.0, 25.0, 25.0); /* Rectangle */
    glPopMatrix();
    glutSwapBuffers();  /* Swap 2 buffer */
}
void spinDisplay(void)
{
    spin = spin + 2.0;  /* Add 2 degrees for every loop action */
    if (spin > 360.0)
        spin = spin - 360.0;
    glutPostRedisplay();  /* Alert: Redraw */
}
/* Change window mode */
void reshape(int w, int h)
{
    glViewport (0, 0, (GLsizei) w, (GLsizei) h); /* change viewport */
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-50.0, 50.0, -50.0, 50.0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
/* Mouse interaction */
void mouse(int button, int state, int x, int y) 
{
    switch (button) {
    case GLUT_LEFT_BUTTON:  /* left mouse */
        if (state == GLUT_DOWN)
            glutIdleFunc(spinDisplay); /* idle mode switch to spinDisplay */
        break;
        //case GLUT_MIDDLE_BUTTON:  /* middle mouse button */
        //if (state == GLUT_DOWN)
        //glutIdleFunc(NULL);
        //break;
    default:
        break;
    }
}
/* main */
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);  /* double buffer */
    glutInitWindowSize (500, 500); 
    glutInitWindowPosition (100, 100);
    glutCreateWindow ("spinning rectangle");
    init ();
    glutDisplayFunc(display); 
    glutReshapeFunc(reshape); /* reshape func (redraw) when window size changed */
    glutMouseFunc(mouse); /* mouse func */
    glutMainLoop();
    return 0;
}

我想将帧缓冲区保存到图像（JPEG、BMP、TIFF）或文件中。你能告诉我怎么做吗？我需要使用一些像 jpeglib、libtiff 这样的库吗？

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