## Draw a color cube and spin it using OpenGL transformation matrices

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 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 until mouse event occurs.

Step 8: Stop

				
Program //Color cube viewer
#include<stdio.h>
#include<GL/glut.h>
GLfloat vertices[][3]= {
{-1.0,-1.0,-1.0},{1.0,-1.0,-1.0}, {1.0,1.0,-1.0},{-1.0,1.0,-1.0}, {-1.0,-1.0,1.0},{1.0,-1.0,1.0}, {1.0,1.0,1.0},{-1.0,1.0,1.0}
};
GLfloat colors[][3]= {
{0.0,0.0,0.0},{0,0.0,0.0}, {1.0,1.0,0.0},{0.0,1.0,1.0}, {0.0,0.0,1.0},{1.0,0.0,1.0}, {1.0,1.0,1.0},{0.0,1.0,1.0}
};
void polygon(int a,int b,int c,int d)
{
glBegin(GL_POLYGON);
glColor3fv(colors[a]);
glVertex3fv(vertices[a]);
glColor3fv(colors[b]);
glVertex3fv(vertices[b]);
glColor3fv(colors[c]);
glVertex3fv(vertices[c]);
glColor3fv(colors[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);
//similarly for remaining 5 faces
}
static GLfloat theta[]={0.0,0.0,0.0};
//angle of rotation along each axis
static GLint axis=2;//current axis
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glRotatef(theta[0],1.0,0.0,0.0);//for x axis
glRotatef(theta[1],0.0,1.0,0.0);
glRotatef(theta[2],0.0,0.0,1.0); // similarly for y and z axis
colorcube();
glutSwapBuffers();
}
void spinCube()
{
theta[axis]+=5.0;
if(theta[axis]>360.0)
theta[axis]-=360.0;
glutPostRedisplay();
}
void mouse(int btn,int state,int x,int y)
{
if(btn==GLUT_LEFT_BUTTON&&state==GLUT_DOWN)axis=0;//x axis rotation
if(btn==GLUT_MIDDLE_BUTTON&&state==GLUT_DOWN)
axis=1;//y axis rotn
if(btn==GLUT_RIGHT_BUTTON&&state==GLUT_DOWN)
axis=2; //similarly for y and z axis
}
void myReshape(int w,int h)// common reshape func for all prgrms
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
if(w<=h)
glOrtho(-2.0,2.0,-2.0*(GLfloat)h/(GLfloat)w,2.0*(GLfloat)h/(GLfloat)w,- 10.0,10.0);
else
glOrtho(-2.0*(GLfloat)w/(GLfloat)h,2.0*(GLfloat)w/(GLfloat)h,-2.0,2.0,- 10.0,10.0);
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 viewer");
glutReshapeFunc(myReshape);
glutDisplayFunc(display);
glutMouseFunc(mouse);
glutIdleFunc(spinCube);
glEnable(GL_DEPTH_TEST);
glutMainLoop();
return 0;
}