prog3-cube_spin.c

// 3. Draw a colour cube and spin it using OpenGL transformation matrices.

/*
ALGORITHM:
1. Initialize vertices, normal’s and colors of the color cube. Also initialize theta and axis.

2. Define main()
		- Enable display mode as double and depth buffer.
		- Register mouse and idle callback function.
		- Enable depth test.

3. Define reshape () enabling glOrtho.

4. Define mouse callback mouse(), coding for left, middle and right buttons for x, y and z axis respectively.

5. Define idle callback spincube()
		- Increment theta for every click.
		- Reinitialize theta
		- If theta > 360 then theta = 0, Call display()

6. Define callback function display()
		- Load identity matrix.
		- Define rotation function for x, y & z axis.
		- Draw the color cube using right hand rule.
		- Swap buffers for there is animation in the scene
*/

#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)
{
/* draw a polygon via list of vertices */

 	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)
{

/* 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(void)
{
/* 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] += 1.0;
	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);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutCreateWindow("Rotating a Color Cube");
    glutReshapeFunc(myReshape);
    glutDisplayFunc(display);
    glutIdleFunc(spinCube);
    glutMouseFunc(mouse);
    glEnable(GL_DEPTH_TEST);
    glutMainLoop();
    return 0;
}