/* rotating cube with color interpolation */

/* demonstration of use of homogeneous-coordinate transformations
and simple data structure for representing cube from Chapter 4 */

/*colors are assigned to the vertices */
/*cube is centered at origin */

#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 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)
{

/* draw a polygon via list of vertices */

 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()
{

/* map vertices to faces */

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;

void display()
{

/* display callback, clear frame buffer and z buffer,
   rotate cube and draw, swap buffers */

 glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 glLoadIdentity();
 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 spinCube()
{

/* idle callback, spin cube 2 degrees about selected axis */

 theta[axis] += 2.0;
 if( theta[axis] > 360.0 ) theta[axis] -= 360.0;
 /* display(); */
 glutPostRedisplay();
}

void mouse(int btn, int state, int x, int y)
{

/* mouse callback, selects an axis about which to rotate */

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;
}

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);

/* need both double buffering and z buffer */

    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutCreateWindow("colorcube");
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
    glutIdleFunc(spinCube);
    glutMouseFunc(mouse);
    glEnable(GL_DEPTH_TEST); /* Enable hidden-surface removal */
    glutMainLoop();
}
