# Dynamic Lighting in OpenGL using GLUT

This is a simple program to show dynamic lighting. The heavy lifting is done in the shadePolygons() function which determines the luminosity of the surface of the cube according to the angle.

``````#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "GL/glut.h"

void init();
void display();
void myIdle();
int main(int argc, char** argv);
void shadePolygons(double x[], double y[], double z[], double kr, double kg, double kb);

float xNear = -3, xFar = 3, yNear = -3, yFar = 3, zNear = 3, zFar = -3;
double lightPos[3] = {-60, 10, 20};
double Id = 4.0;
double Ia = 1.0;
int direction = 1;

void shadePolygons(double x[], double y[], double z[], double kr, double kg, double kb)
{
float vx = x[1] - x[0];
float vy = y[1] - y[0];
float vz = z[1] - z[0];

float wx = x[2] - x[1];
float wy = y[2] - y[1];
float wz = z[2] - z[1];

float Nx = vy*wz-vz*wy;
float Ny = vx*wz-vz*wx;
float Nz = vx*wy-vy*wx;

float Lx = lightPos[0] - ((x[0]+x[1])/2);
float Ly = lightPos[1] - ((y[0]+y[1])/2);
float Lz = lightPos[2] - ((z[0]+z[1])/2);

float LdotN = (Lx*Nx)+(Ly*Ny)+(Lz*Nz);
float normL = sqrt(Lx*Lx + Ly*Ly + Lz*Lz);
float normN = sqrt(Nx*Nx + Ny*Ny + Nz*Nz);

float lightAmt = ( (LdotN*Id)/(normL*normN) );
lightAmt = lightAmt + Ia;
lightAmt = lightAmt / (Ia+Id);
glColor3f(kr*lightAmt, kg*lightAmt, kb*lightAmt);
glBegin(GL_POLYGON);
glVertex3f(x[0], y[0], z[0]);
glVertex3f(x[1], y[1], z[1]);
glVertex3f(x[2], y[2], z[2]);
glVertex3f(x[3], y[3], z[3]);
glEnd();
}

void init()
{
glClearColor(0, 0, 0, 0);
glMatrixMode(GL_PROJECTION);
glOrtho(xNear, xFar, yNear, yFar, zNear, zFar);
glRotatef(30, -1, 1, 0);
}

void display()
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glColor3f(1,1,1);

char title[15];
sprintf(title,"%f", lightPos[0]);
glutSetWindowTitle(title);

double face1x[] = {0,0,1,1};
double face1y[] = {0,0,0,0};
double face1z[] = {0,-1,-1,0};

double face2x[] = {0,0,1,1};
double face2y[] = {0,-1,-1,0};
double face2z[] = {-1,-1,-1,-1};

double face3x[] = {1,1,1,1};
double face3y[] = {0,-1,-1,0};
double face3z[] = {-1,-1,0,0};

double face4x[] = {0,0,1,1};
double face4y[] = {-1,-1.5,-1.5,-1};
double face4z[] = {-1,-1.5,-1.5,-1};

double face5x[] = {1,1,2,2};
double face5y[] = {0,-1,-1,0};
double face5z[] = {0,0,0,0};
glutSwapBuffers();
}

void myIdle()
{
lightPos[0] = lightPos[0]+direction;
if(lightPos[0] >= 60)
direction = direction*(-1);
if(lightPos[0] <= -60)
direction = direction*(-1);
double zzz=0;
for (int i=0; i<2000000; i++)
zzz = sqrt((double)i);
glutPostRedisplay();
}

int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowSize(400,400);
glutInitWindowPosition(20,20);