## OpenGL to draw a color cube and allow the user to move the camera

Algorithm:
Step 1: Start
Step 2: Render the cube using the array of vertices.
Step 3: Obtain the co-ordinates of the cube with the origin at the center of the cube.
Step 4: Draw the 6 faces of the cube using three points.
Step 5: Increment the angle w.r.t current axis by user specified value.
Step 6: Display the cube on the screen and rotate by the current value of angle around current axis.
Step 7: Repeat step 4 and 5.
Step 8: Stop

				
#include<stdio.h>
#include<GL/glut.h>
GLfloat vertices[][3]=
{
{-2.0,-2.0,-2.0},{2.0,-2.0,-2.0}, {2.0,2.0,-2.0},{-2.0,2.0,-2.0}, {-2.0,-2.0,2.0},{2.0,-2.0,2.0}, {2.0,2.0,2.0},{-2.0,2.0,2.0}
};
GLfloat normals[][3]=
{
{-2.0,-2.0,-2.0},{2.0,-2.0,-2.0}, {2.0,2.0,-2.0},{-2.0,2.0,-2.0}, {-2.0,-2.0,2.0},{2.0,-2.0,2.0}, {2.0,2.0,2.0},{-2.0,2.0,2.0} }; GLfloat colors[][3]= { {0.0,0.0,0.0},{2.0,0.0,0.0}, {2.0,2.0,0.0},{0.0,2.0,0.0}, {0.0,0.0,2.0},{2.0,0.0,2.0}, {2.0,2.0,2.0},{2.0,0.0,2.0}
};
void polygon(int a,int b,int c,int d)
{
glBegin(GL_POLYGON);
glColor3fv(colors[a]);
glNormal3fv(normals[a]);
glVertex3fv(vertices[a]);
glColor3fv(colors[b]);
glNormal3fv(normals[b]);
glVertex3fv(vertices[b]);
glColor3fv(colors[c]);
glNormal3fv(normals[c]);
glVertex3fv(vertices[c]);
glColor3fv(colors[d]);
glNormal3fv(normals[d]);
glVertex3fv(vertices[d]);
glEnd();
}
void colorCube(void)
{
polygon(0,3,2,1);
polygon(2,3,7,6);
polygon(0,4,7,3);
polygon(1,2,6,5);
polygon(4,5,6,7);
polygon(0,1,5,4);
}
static GLfloat theta[]={0.0,0.0,0.0};
static GLint axis=2;
static GLdouble viewer[]={0.0,0.0,5.0};
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
glClearColor(1.0,1.0,1.0,1.0);
gluLookAt(viewer[0],viewer[1],viewer[2],0.0,0.0,0.0,0.0,1.0,0.0);// define a viewing
transformation glRotatef(theta[0],1.0,0.0,0.0);
glRotatef(theta[1],0.0,1.0,0.0);
glRotatef(theta[2],.0,0.0,1.0);
colorCube();
glutSwapBuffers();
}
void mouse(int btn,int state,int x,int y)
{
if(btn==GLUT_LEFT_BUTTON && state==GLUT_DOWN) axis=0;
if(btn==GLUT_MIDDLE_BUTTON && state==GLUT_DOWN) axis=1;
if(btn==GLUT_RIGHT_BUTTON && state==GLUT_DOWN) axis=2;
theta[axis]+=2.0;
if(theta[axis]>360.0)theta[axis]-=360.0;
glutPostRedisplay();
}
void keys(unsigned char key,int x,int y)
{
if(key=='x') viewer[0] -= 1.0;
if(key=='X') viewer[0] += 1.0;
if(key=='y') viewer[1] -= 1.0;
if(key=='Y') viewer[1] += 1.0;
if(key=='z') viewer[2] -= 1.0;
if(key=='Z') viewer[2] += 1.0;
glutPostRedisplay();
}
void myReshape(int w,int h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if(w<=h)
glFrustum(-2.0,2.0,- 2.0*(GLfloat)h/(GLfloat)w,2.0*(GLfloat)h/(GLfloat)w,2.0,20.0);
else
glFrustum(-2.0,2.0,- 2.0*(GLfloat)w/(GLfloat)h,2.0*(GLfloat)w/(GLfloat)h,2.0,20.0);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc,char**argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
glutInitWindowSize(500,500);
glutCreateWindow("color cube");
glutReshapeFunc(myReshape);
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutKeyboardFunc(keys);
glEnable(GL_DEPTH_TEST);
glutMainLoop();
return 0;
}