Aim:

Program to draw a color cube and allow the user to move the camera suitably to experiment with perspective viewing. Use OpenGL functions.

Algorithm

1. Choose appropriate coordinates to make a cube
2. Rotate or move the cube by a small variation on user input
3. Repeat

Code moveCube.c

#include<stdlib.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 normals[][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}, {1.0,0.0,0.0}, {1.0,1.0,0.0}, {0.0,1.0,0.0}, {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]);
    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()
{
    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();
    gluLookAt(viewer[0],viewer[1],viewer[2],0.0,0.0,0.0,0.0,1.0,0.0);
    glRotatef(theta[0],1.0,0.0,0.0);
    glRotatef(theta[1],0.0,1.0,0.0);
    glRotatef(theta[2],0.0,0.0,1.0);
    colorcube();
    glFlush();
    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;
    display();
}

void myReshape(int w,int h)
{
    glViewport(0,0,w,h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    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("colorcube viewer");
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
    glutMouseFunc(mouse);
    glutKeyboardFunc(keys);
    glEnable(GL_DEPTH_TEST);
    glutMainLoop();
}

Output:

Commands for execution:-

• Open a terminal and Change directory to the file location in both the terminals.
• compile as gcc -lGLU -lGL -lglut moveCube.c -o movecube
• If no errors, run as ./movecube

Screenshots:-