Добавление тени в OpenGL

У меня есть очень простой код, который просто рисует здание, я хочу добавить тень от здания. Я перепробовал много примеров кода, но либо они слишком сложны с большим количеством нарисованных объектов. или просто слишком расплывчато Как я могу получить тень от моего здания?

#include "GLee/GLee.h" //GL header file, including extensions
#include "glut.h"#include <stdio.h>
#include <conio.h>
#include <math.h>
#include "tga.h"#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#include <stdio.h>
char  g_SelectedColor = 'w';
int   g_Width;
int   g_Height;
int a=0.0 ,b=0.0, c=500, d=0.0, e=0.0, f=0.0,g=0.0,h=1.0,i=0.0;

static int rotationAngle=0;
void init();
void myMouseFunction( int button, int state, int mouseX, int mouseY );
void myKeyboardFunction( unsigned char key, int mouseX, int mouseY );
void Reshape( int width, int height );
void timer( int val );
void display();
void drawBuilding();
void menu(int);
// Assign a default value
float light_diffuse[]   = { 0.8, 0.8, 0.8, 1.0 };
float light_ambient[]   = { 0.1, 1.1, 0.0, 0.0 };
float light_specular[]  = { 0.5, 0.5, 0.9, 1.0 };
float light_position[]  = { 0.0, 10.0, 0.0, 1.0 };
void selectMessage( int val )
{
if(val==2)
{
glBegin(GL_POLYGON);
glVertex3f(0.0,0.0,0.0);
glVertex3f(0.0,200.0,0.0);
glVertex3f(200.0,200.0,0.0);
glVertex3f(200.0,0.0,0.0);
glVertex3f(0.0,0.0,0.0);
glEnd();
}
}
int main(int argc, char** argv)
{
glutCreateMenu(menu);
glutAddMenuEntry("View1", 1);
glutAddMenuEntry("View2", 2);
glutAttachMenu(GLUT_RIGHT_BUTTON);g_Width =1200; g_Height = 600;
glutInitDisplayMode( GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
// glutInitWindowSize( g_Width, g_Height );
//glutFullScreen();
glutInitWindowPosition( 50, 50 );
glutCreateWindow( "CHECK" );
init();
glutMouseFunc( myMouseFunction );
glutKeyboardFunc( myKeyboardFunction );

glutReshapeFunc( Reshape );
glutDisplayFunc( display );
glutMainLoop();
return 0;
}
void init(void)
{

glutAttachMenu(GLUT_RIGHT_BUTTON);
glClearColor( 1.0, 1.0, 1.0, 1.0 );
glMatrixMode( GL_PROJECTION );
glLoadIdentity();
gluPerspective( 50.0, 1.0, 200, 1000 );
//glOrtho( -5.0, +5.0, -5.0, +5.0, +5.0, -5.0 );
glLightfv(GL_LIGHT0, GL_DIFFUSE,  light_diffuse);
glLightfv(GL_LIGHT0, GL_AMBIENT,  light_ambient );
glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular );
glLightfv(GL_LIGHT0, GL_POSITION, light_position);
glShadeModel(GL_SMOOTH);
//glShadeModel(GL_FLAT);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST);
//glCullFace(GL_FRONT_AND_BACK );
glDisable(GL_CULL_FACE );
glMatrixMode( GL_MODELVIEW );
if ( loadTGA ("im1.tga", 10 ) == false )
printf ("\nError: File myQuakeTexture.tga not found!");

if ( loadTGA ("im2.tga", 11 ) == false )
printf ("\nError: File myQuakeTexture.tga not found!");
}
void myMouseFunction( int button, int state, int mouseX, int mouseY )
{
}
void myKeyboardFunction( unsigned char key, int mouseX, int mouseY )
{

switch( key )
{
case 'r':
{

glClearColor( 0.0, 0.0, 1.0, 1.0 );
glRotatef( rotationAngle++, 0.0, 1.0, 0.0 );
//  drawBuilding();
//display();

}
case 'R':
case 'g':

case 'G':
case 'b':

case 'B':
case 'w':
case 'W':
g_SelectedColor = key;
break;
case '1':

case '2':
case '3':
case '4':
case '5':
break;
case 27:  // Esc key
exit(0);
break;  // redundant
default:
break;
}
}
void Reshape( int width, int height )
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
g_Width  = width;
g_Height = height;
glViewport (0, 0, g_Width, g_Height);
glMatrixMode (GL_PROJECTION);
glLoadIdentity ();
gluPerspective( 50.0, 1.0, 200, 1000 );
//glOrtho( -5.0, +5.0, -5.0, +5.0, +5.0, -5.0 );;
}
void timer( int val )
{
display();
}
static float firstAngle=0;
void drawBuilding()
{
float DoorMaterial[4] = { 0.5, 0.2, 1.3, 1.0 };
//

glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D ,10);
glTranslatef(30,-180,0);
//Building 1
//Front
glBegin(GL_POLYGON);
glVertex3f(0.0,0.0,0.0);
glTexCoord2d(1,1);
glVertex3f(0.0,400.0,0.0);
glTexCoord2d(0,1);
glVertex3f(70.0,400.0,0.0);
glTexCoord2d(0,0);
glVertex3f(70.0,0.0,0.0);
glTexCoord2d(1,0);
glVertex3f(0.0,0.0,0.0);
glEnd();
//Back
glBegin(GL_POLYGON);
glVertex3f(0.0,0.0,-50.0);
glTexCoord2d(1,1);
glVertex3f(0.0,400.0,-50.0);
glTexCoord2d(0,1);
glVertex3f(70.0,400.0,-50.0);
glTexCoord2d(0,0);
glVertex3f(70.0,0.0,-50.0);
glTexCoord2d(1,0);
glVertex3f(0.0,0.0,-50.0);
glEnd();
//Left
glBegin(GL_POLYGON);
glVertex3f(0.0,0.0,0.0);
glTexCoord2d(1,1);
glVertex3f(0.0,400.0,0.0);
glTexCoord2d(0,1);
glVertex3f(0.0,400.0,-50.0);
glTexCoord2d(0,0);
glVertex3f(0.0,0.0,-50.0);
glTexCoord2d(1,0);
glVertex3f(0.0,0.0,0.0);
glEnd();
//Right
glBegin(GL_POLYGON);
glVertex3f(70.0,0.0,0.0);
glTexCoord2d(1,1);
glVertex3f(70.0,400.0,0.0);
glTexCoord2d(0,1);
glVertex3f(70.0,400.0,-50.0);
glTexCoord2d(0,0);
glVertex3f(70.0,0.0,-50.0);
glTexCoord2d(1,0);
glVertex3f(70.0,0.0,0.0);
glEnd();
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D ,11);

}
void menu(int item)
{
switch (item)
{
case 1:
{

a=-500, b=0, c=300,d=0,e=0,f=0,g=0,h=1,i=0;}

break;

case 2:
{
a=0, b=300, c=500,d=0,e=0,f=0,g=0,h=1,i=0;
drawBuilding();
}
}
}
void display()
{
glRotatef( rotationAngle++, 0.0, 1.0, 0.0 );
glutFullScreen();
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt( a, b, c,
d, e,  f,
g, h, i );

glRotatef( rotationAngle++, 0.0, 1.0, 0.0 );
//
drawBuilding();
glDisable(GL_TEXTURE_2D);// this tells glut to call the 'timer' function in 33 milliseconds
// i.e. this way we will draw 1000/33 = 30 times a second
glutTimerFunc( 33, timer, 0 );
glutSwapBuffers();
printf(".");
}