Este es el archivo .h

#ifndef FD_demonstracion_h_
#define FD_demonstracion_h_
/* Header file generated with fdesign. */

/**** Callback routines ****/

void Salir(FL_OBJECT *ob,long data);    
void Rotar(FL_OBJECT *ob,long data);    


/**** Forms and Objects ****/

typedef struct {
        FL_FORM *demonstracion;
        
        FL_OBJECT *canvas;              
        FL_OBJECT *boton_rotar;         
        FL_OBJECT *boton_detener;       
        FL_OBJECT *boton_ok;                    
        
        void *vdata;
        long ldata;
} FD_demonstracion;

extern FD_demonstracion * create_form_demonstracion(void);

#endif /* FD_demonstracion_h_ */

Este es el archivo .c

/* Form definition file generated with fdesign. */

#define v3f glVertex3f          

#include "forms.h"
#include "prueba.h"
#include "GL/gl.h"              
#include "GL/glx.h"

FD_demonstracion *display;      

char rotar=1;                   

int idle_cb(XEvent *ev,void *data); 
void Detener(FL_OBJECT *ob,long data);  
int InitOGL(FL_OBJECT *ob, Window win,int w,int h, XEvent *xev,void *ud);
void Figura(void);              

FD_demonstracion *create_form_demonstracion(void)
{
  FL_OBJECT *obj;
  FD_demonstracion *fdui = (FD_demonstracion *) fl_calloc(1, sizeof(FD_demonstracion));

  fdui->demonstracion = fl_bgn_form(FL_NO_BOX, 460, 520);
  obj = fl_add_box(FL_UP_BOX,0,0,460,520,"");

        
  fdui->canvas= obj = fl_add_glcanvas(FL_NORMAL_CANVAS,80,200,300,290,"");      /*  ojo, gl aqui! */

  fdui->boton_ok= obj = fl_add_button(FL_NORMAL_BUTTON,360,20,80,50,"OK");
    fl_set_object_lsize(obj,FL_HUGE_SIZE);
    fl_set_object_lstyle(obj,FL_BOLD_STYLE+FL_ENGRAVED_STYLE);

  fdui->boton_rotar= obj = fl_add_button(FL_NORMAL_BUTTON,30,120,260,60,"ROTAR");
    fl_set_object_lsize(obj,FL_HUGE_SIZE);
    fl_set_object_lstyle(obj,FL_NORMAL_STYLE+FL_ENGRAVED_STYLE);
    fl_set_object_callback(obj,Rotar,0);        

  fdui->boton_detener= obj = fl_add_button(FL_NORMAL_BUTTON,30,50,260,60,"DETENER");
    fl_set_object_lsize(obj,FL_HUGE_SIZE);
    fl_set_object_lstyle(obj,FL_NORMAL_STYLE+FL_ENGRAVED_STYLE);
    fl_set_object_callback(obj,Detener,0);      

  fl_end_form();

  return fdui;
}
/*---------------------------------------*/

void main(int argc,char *argv[])
{
        FL_OBJECT *controla;    
        
        
        fl_initialize(argv[0],"GlDemo",0,0,&argc,argv); 
        display=create_form_demonstracion();    
        fl_add_canvas_handler(display->canvas,Expose,InitOGL,0);        
        fl_set_idle_callback(idle_cb,0);        

        fl_show_form(display->demonstracion,FL_PLACE_CENTER|FL_FREE_SIZE,
        FL_FULLBORDER,"Open GL demo");                  

        while((controla = fl_do_forms()) != display->boton_ok); 
}



int InitOGL(FL_OBJECT *ob, Window win,int w,int h, XEvent *xev, void *ud)
{

/* La primera parte de esta funcion inicializa OpenGL con los parametros
   que diran como se visualiza. */

        glViewport(0,0,(GLint)w,(GLint)h);
        glDrawBuffer(GL_FRONT);
        glClearColor(0.0,0.0,0.0,0.0);
        glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();

        glOrtho(-5.0,5.0,-5.0,5.0,1.0,100.0);
        glTranslatef(0,0,-5);

        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

        glCullFace(GL_BACK);
        glEnable(GL_CULL_FACE);
        glScalef(2.0,2.0,2.0);
        
        glShadeModel(GL_SMOOTH);


        return 0;
}

int idle_cb(XEvent *ev,void *data)
{
        
        if(rotar)
        {
                glDrawBuffer(GL_BACK);
                glClearColor(0.5,0.5,0.5,0.0);
                glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

                glRotatef(1.0,1.0,2.0,-3.0);
        
                Figura();                               

                glXSwapBuffers(fl_display, fl_get_canvas_id(display->canvas));  
        }


}



void Figura( void )
{
   glColor3f( 1.0, 0.0, 0.0 );
   glBegin(GL_POLYGON);
   v3f( 1.0, 1.0, 1.0 );   v3f( 1.0, -1.0, 1.0 );
   v3f( 1.0, -1.0, -1.0 ); v3f( 1.0, 1.0, -1.0 );
   glEnd();

   glColor3f( 0.5, 0.0, 0.0 );
   glBegin(GL_POLYGON);
   v3f( -1.0, 1.0, 1.0 );   v3f( -1.0, 1.0, -1.0 );
   v3f( -1.0, -1.0, -1.0 ); v3f( -1.0, -1.0, 1.0 );
   glEnd();

   glColor3f( 0.0, 1.0, 0.0 );
   glBegin(GL_POLYGON);
   v3f(  1.0, 1.0,  1.0 ); v3f(  1.0, 1.0, -1.0 );
   v3f( -1.0, 1.0, -1.0 ); v3f( -1.0, 1.0,  1.0 );
   glEnd();

   glColor3f( 0.0, 0.5, 0.0 );
   glBegin(GL_POLYGON);
   v3f(  1.0, -1.0,  1.0 ); v3f( -1.0, -1.0,  1.0 );
   v3f( -1.0, -1.0, -1.0 ); v3f(  1.0, -1.0, -1.0 );
   glEnd();

   glColor3f( 0.0, 0.0, 1.0 );
   glBegin(GL_POLYGON);
   v3f(  1.0,  1.0,  1.0 ); v3f( -1.0,  1.0,  1.0 );
   v3f( -1.0, -1.0,  1.0 ); v3f(  1.0, -1.0,  1.0 );
   glEnd();

   glColor3f( 0.0, 0.0, 0.5 );
   glBegin(GL_POLYGON);
   v3f(  1.0, 1.0, -1.0 ); v3f(  1.0,-1.0, -1.0 );
   v3f( -1.0,-1.0, -1.0 ); v3f( -1.0, 1.0, -1.0 );
   glEnd();
}


void Rotar(FL_OBJECT *ob,long data)
{
        rotar=1;
}
void Detener(FL_OBJECT *ob,long data)
{
        rotar=0;
}