问opengl --如何调用函数并从头开始绘制(从菜单选项)

EN

 void mandelbrot();     
 void mandelbrot_black();

 GLsizei width = 600;
 GLsizei height = 600; 
 GLfloat AspectRatio;
 int max = 500;
 double xpos=0,ypos=0;
 int CLEARFLAG=1;


  double xmax = 2.0;
  double xmin = -2.0; 
  double ymax = 2.0;
  double ymin = -2.0;

  using namespace std;

  void display()
 {
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
  gluOrtho2D(-2, width, -2, height);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glClear(GL_COLOR_BUFFER_BIT| GL_DEPTH_BUFFER_BIT );
  mandelbrot();
  glutSwapBuffers();
  }


  void reshape(GLsizei w, GLsizei h) {

  width=w; height=h;
  glViewport(0,0,width,height);
  glutPostRedisplay();
   }



  void setXYpos(int px, int py)
    {  
     xpos=xmin+(xmax-xmin)*px/width;
     ypos=ymax-(ymax-ymin)*py/height;

     }



   void mouse(int button, int state, int x, int y)
  {
if(button==GLUT_LEFT_BUTTON && state==GLUT_DOWN) {CLEARFLAG=0; setXYpos(x,y);}

glutPostRedisplay();
  }

void mandelbrot()
 {
 ...}

void mandelbrot_black(){
...}

void mymenu(int n)
{
  switch(n) {

   case 1: zoom_in();break;
   case 2: zoom_out();break;
   case 3: mandelbrot_black();break;
   case 4: exit(0);
     }

   glutPostRedisplay();
    }




   void SetupMenu()
   {

glutCreateMenu(mymenu);
glutAddMenuEntry("zoom in",1);
glutAddMenuEntry("zoom out",2);
glutAddMenuEntry("black&white",3);
glutAddMenuEntry("exit",4);
glutAttachMenu(GLUT_RIGHT_BUTTON);
    } 

     int main(int argc, char *argv[])
     {

     glutInit(&argc, argv);
     glutInitWindowSize(600, 600);
     glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
     glutCreateWindow("Mandelbrot");
     glutDisplayFunc(display);
     glutReshapeFunc(reshape);
     glutMainLoop();

     return 0;
      }