OpenGL - Cube rotation along different axes

CubeRotate.c

#include<stdio.h>
#include<GL/glut.h>
#include<math.h>

float v[][3] = { {-1,-1,-1} ,{ -1,1,-1 } ,{ 1,1,-1 } ,{ 1,-1,-1 } ,{ -1,-1,1 } ,{ -1,1,1 } ,{ 1,1,1 } ,{ 1,-1,1 }  }; // 8 vertices of the cube with origin as its centroid
int t[] = { 0,0,0 };  // degree of rotation along {x,y,z} 
int ax = 2; // axis of rotation


void init()
{
	glMatrixMode(GL_PROJECTION);
	glOrtho(-4, 4, -4, 4, -10, 10); // https://www.khronos.org/registry/OpenGL-Refpages/gl2.1/xhtml/glOrtho.xml (check)
	glMatrixMode(GL_MODELVIEW);  // place where your object gets modelled

}


void polygon(int a, int b, int c, int d)  // function used to draw one face of a cube at a time 
{
	glBegin(GL_POLYGON);	// draw the square using polygon
	glVertex3fv(v[a]);		// 4 coordinates of the square face are give.. 
	glVertex3fv(v[b]);		// each v[i] contains 3 values (x,y,z) which denotes a point in 3D plane
	glVertex3fv(v[c]);
	glVertex3fv(v[d]);
	glEnd();
}



void colorcube()		//function used to color each face of the cube seperately 
{
	// 0,1,2,3....8 are the index postions of the 2D matrix v[][] which holds the coordinates of each vertex of the cube

	glColor3f(0, 0, 1);		//color of front square
	polygon(0, 1, 2, 3);	// drawing the front square

	glColor3f(0, 1, 1);		// color of the left square
	polygon(4, 5, 6, 7);	// drawing the left square

	glColor3f(0, 1, 0);		// color of the right square
	polygon(0, 1, 5, 4);	// drawing the right square

	glColor3f(1, 0, 0);		// color of the top square
	polygon(2, 6, 7, 3);	// drawing the top square

	glColor3f(1, 1, 0);		// color of the bottom square
	polygon(0, 4, 7, 3);	// drawing the bottom square

	glColor3f(1, 0, 1);		// color of the back square
	polygon(1, 5, 6, 2);	// drawing the back square


}


void spincube()
{
	t[ax] += 1;		// rotating the cube by 1 degree at a time on the given axis "ax" ( ax = 0 is x axis , ax =1 is y axis , ax =2 is z axis)
	if (t[ax] == 360)
		t[ax] -= 360;	// when the rotation along any axis reaches 360 reset the axis to 0
	glutPostRedisplay();	// calling the display again.. 

}


void mouse(int btn, int state, int x, int y)  // function is used to capture the events of the mouse and rotate cube accordingly
{
	if (btn == GLUT_LEFT_BUTTON && state == GLUT_DOWN)	// on left click, state of the left button is set to DOWN ...and ax =0
		ax = 0;											//ie rotate along x axis

	if (btn == GLUT_MIDDLE_BUTTON && state == GLUT_DOWN)// on middle click, state of the middle button is set to DOWN .. and ax=1
		ax = 1;											//ie rotate along y axis

	if (btn == GLUT_RIGHT_BUTTON && state == GLUT_DOWN)// on right click, state of the right button is set to DOWN.. and ax=2
		ax = 2;											//ie rotate along z axis

}



void display()	// display function
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //clears the color buffer and depth buffer
	glClearColor(1, 1, 1, 1);	//sets the backround screen color
						
	glLoadIdentity();	//loads identity matrix into modelview

	//glrotatef(angle of rotation,x,y,z)
	glRotatef(t[0], 1, 0, 0);	//rotate cube at an angle of t[0] degrees wrt vector(1,0,0)
	glRotatef(t[1], 0, 1, 0);	//rotate cube at an angle of t[1] degrees wrt vector(0,1,0)
	glRotatef(t[2], 0, 0, 1);	//rotate cube at an angle of t[2] degrees wrt vector(0,0,1)

	colorcube();	// call the function to color each square of cube with different colors

	glutSwapBuffers();	/* this program contains 2 buffers .. one buffer stores the current object and the other buffer stores the 
						next view of the object .. in this case lets say if buffer 1 stores cube rotated by 5 degree and the buffer 2 stores 
						cube that is rotated by 5 + 1 degree.. swapping of these buffers will make it seem animated such a way that u see
						cube rotating*/

	glFlush();	

}


void main(int argc, char **argv)
{

	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH); // no idea xD
	glutInitWindowPosition(100, 100); // set window position
	glutInitWindowSize(500, 500);	//set window size
	glutCreateWindow("Cube rotation");

	init();
	glutIdleFunc(spincube);	/*idle function helps the spincube function called continuosly .. 
							this is what makes cube rotate even when you are not clicking the 
							mouse buttons */

	glutMouseFunc(mouse);	// calls the mouse function... glutmousefunc captures your mouse activity
	glEnable(GL_DEPTH_TEST);	//enabling the depth buffer
	glutDisplayFunc(display);
	glutMainLoop();

}