// when you set the glPushMatrix(); it distinguishes where to start the transformations for an object
// to set where to stop these transformations you would call glPopMatrix();

// for instance, if you take the push and pop matrix code out of this file
// cube1 would act normal, but cube2 would be rotating it's own way as well
// as including the rotation from cube1

#include <GL/gl.h>
#include <GL/glut.h>

GLfloat angle = 0.0; //angle for cube1
GLfloat tangle = 0.0; //angle for cube2

void cube (void) {
	glPushMatrix(); //set where to start the current object transformations
	glTranslatef(1, 0, 0); //move cube1 to the right
	glRotatef(angle, 1.0, 0.0, 0.0);
	glRotatef(angle, 0.0, 1.0, 0.0);
	glRotatef(angle, 0.0, 0.0, 1.0);
	glColor3f(1.0, 0.0, 0.0); //change cube1 to red
	glutWireCube(2);
	glPopMatrix(); //end the current object transformations
}

void cube2 (void) {
	glPushMatrix(); //set where to start the current object transformations
	glTranslatef(-1, 0, 0); //move cube2 to the left
	glRotatef(tangle, 1.0, 0.0, 0.0);
	glRotatef(tangle, 0.0, 1.0, 0.0);
	glRotatef(tangle, 0.0, 0.0, 1.0);
	glColor3f(0.0, 1.0, 0.0); //change cube2 to green
	glutWireCube(2);
	glPopMatrix(); //end the current object transformations
}

void display (void) {
	glClearColor (0.0,0.0,0.0,1.0);
    glClear (GL_COLOR_BUFFER_BIT);
    glLoadIdentity();  
	gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
	cube();
	cube2();
	glutSwapBuffers();
	angle+= 1.0;
	tangle+= 2.0;
}

void reshape (int w, int h) {
	glViewport (0, 0, (GLsizei)w, (GLsizei)h);
	glMatrixMode (GL_PROJECTION);
	glLoadIdentity ();
	gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);
	glMatrixMode (GL_MODELVIEW);
}

int main (int argc, char **argv) {
    glutInit (&argc, argv);
	glutInitDisplayMode (GLUT_DOUBLE);
	glutInitWindowSize (500, 500);
	glutInitWindowPosition (100, 100);
    glutCreateWindow ("A basic OpenGL Window");
    glutDisplayFunc (display);
	glutIdleFunc (display);
	glutReshapeFunc (reshape);
    glutMainLoop ();
    return 0;
}