Как сделать так, чтобы в окне, созданом OpenGL, рисовали 2 потока?

-lopengl32 -lglu32 -lglut32 -static

// GLRect.cpp
// Just draw a single rectangle in the middle of the screen
// OpenGL SuperBible, 3rd Edition
// Richard S. Wright Jr.
// [email]rwright@starstonesoftware.com[/email]
 
//#include "../../shared/gltools.h"    // OpenGL toolkit
#define _STDCALL_SUPPORTED
#include <GL\glut.h>
#include <stdio.h>
 
///////////////////////////////////////////////////////////
// Called to draw scene
void RenderScene(void)
    {
    // Clear the window with current clearing color
    glClear(GL_COLOR_BUFFER_BIT);
 
       // Set current drawing color to red
    //           R     G       B
    glColor3f(1.0f, 0.0f, 0.0f);
 
    // Draw a filled rectangle with current color
    glRectf(-25.0f, 25.0f, 25.0f, -25.0f);
 
    // Flush drawing commands
    glFlush();
    }
 
///////////////////////////////////////////////////////////
// Setup the rendering state
void SetupRC(void)
    {
    // Set clear color to blue
    glClearColor(0.0f, 0.0f, 1.0f, 1.0f);
    }
 
 
///////////////////////////////////////////////////////////
// Called by GLUT library when the window has chanaged size
void ChangeSize(int w, int h)
    {
    GLfloat aspectRatio;
 
    // Prevent a divide by zero
    if(h == 0)
        h = 1;
        
    // Set Viewport to window dimensions
    glViewport(0, 0, w/2, h);
 
    // Reset coordinate system
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
 
    // Establish clipping volume (left, right, bottom, top, near, far)
    aspectRatio = (GLfloat)w / (GLfloat)h;
    if (w <= h){  
        glOrtho (-100.0, 100.0, -100 / aspectRatio*2, 100.0 / aspectRatio*2, 1.0, -1.0);
    }
    else{ 
        glOrtho (-100.0 * aspectRatio, 100.0 * aspectRatio, -100.0, 100.0, 1.0, -1.0);
    }
//        glOrtho (-100.0, 100.0, -100 , 100, 1.0, -1.0);
 
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    }
 
///////////////////////////////////////////////////////////
// Main program entry point
int main(int argc, char* argv[])
    {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutCreateWindow("GLRect");
 
 
    glutDisplayFunc(RenderScene);
    glutReshapeFunc(ChangeSize);
 
 
    SetupRC();
    glutMainLoop();
        
    return 0;
    }
 
 
 
//void *taskl(void *X) { 
// pthread_t Threadld; 
// Threadld = pthread_self(); 
//
// printf ("A gl_per= %d\n", gl_per);
// getchar ();
// gl_per++;
// printf ("A gl_per= %d\n", gl_per);
// 
// printf ("TID A= %x\n", *(unsigned int*)Threadld.p);
// return NULL; 
//}