/* Example 2.7.sphere.c: draw a sphere by subdivision */
// by Jim X. Chen; September, 2000

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

#define ESC 27
#define SPACE 32
int Height=400, Width=400;
int depth=0, circleRadius=2, cnt=1; 


static float vdata[6][3] = {
	{1.0, 0.0, 0.0}, {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0},
	{-1.0, 0.0, 0.0}, {0.0, -1.0, 0.0}, {0.0, 0.0, -1.0}
};


void normalize(float v[3]) {
	float d = sqrt(v[0]*v[0]+v[1]*v[1]+v[2]*v[2]);

	if (d == 0) {
		printf("zero length vector");
		return;
	}
	v[0] /= d;	v[1] /= d;	v[2] /= d;
}

void drawtriangle(float *v1, float *v2, float *v3)
{
	glBegin(GL_TRIANGLES);
		glVertex3fv(v1);
		glVertex3fv(v2);
		glVertex3fv(v3);
	glEnd();
}


void subdivideSphere(float *v1, float *v2, float *v3, long depth)
{
	float v12[3], v23[3], v31[3];
	int i;

	if (depth == 0) {
		glColor3f(v1[0]*v1[0], v2[1]*v2[1], v3[2]*v3[2]);
		drawtriangle(v1, v2, v3);
		return;
	}
	for (i = 0; i < 3; i++) {
		v12[i] = v1[i]+v2[i];
		v23[i] = v2[i]+v3[i];
		v31[i] = v3[i]+v1[i];
	}
	normalize(v12);
	normalize(v23);
	normalize(v31);
	subdivideSphere(v1, v12, v31, depth - 1);
	subdivideSphere(v2, v23, v12, depth - 1);
	subdivideSphere(v3, v31, v23, depth - 1);
	subdivideSphere(v12, v23, v31, depth - 1);
}


void drawSphere(void)
// draw a cone with z=height and bottom in xy plane

{
	subdivideSphere(vdata[0], vdata[1], vdata[2], depth);
	subdivideSphere(vdata[0], vdata[2], vdata[4], depth);
	subdivideSphere(vdata[0], vdata[4], vdata[5], depth);
	subdivideSphere(vdata[0], vdata[5], vdata[1], depth);

	subdivideSphere(vdata[3], vdata[1], vdata[5], depth);
	subdivideSphere(vdata[3], vdata[5], vdata[4], depth);
	subdivideSphere(vdata[3], vdata[4], vdata[2], depth);
	subdivideSphere(vdata[3], vdata[2], vdata[1], depth);


}


void display(void)
{ 
	if (circleRadius>Width/2 || circleRadius==1) 
	{
		cnt=-cnt; 
		depth++;
		depth = depth % 5;
	}

	circleRadius+=cnt;

	// clears both framebuffer and zbuffer
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glPushMatrix();
		glScalef(circleRadius, circleRadius, circleRadius);
		drawSphere();
	glPopMatrix();

	glutSwapBuffers();
}



static void Reshape(int w, int h)
{
    glClearColor (0.0, 0.0, 0.0, 1.0);

	// enables depth test for hidden surface removal
 	glEnable(GL_DEPTH_TEST);

	Width = w; Height = h; 

    glViewport (0, 0, Width, Height);

    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glOrtho(-Width/2, Width/2, -Height/2, Height/2, -Width, Width); 
    glMatrixMode (GL_MODELVIEW);
    glLoadIdentity ();
}



static void Key(unsigned char key, int x, int y)
{ 
    switch (key) {
      case ESC:
			exit(0);
	  case SPACE: 
			glutIdleFunc(NULL); display();
			break; 
	  default: 
			glutIdleFunc(display); 
    }
}


int main(int argc, char **argv)
{
    glutInit(&argc, argv);
 	glutInitDisplayMode(GLUT_DOUBLE);
    glutInitWindowSize(Width, Height);
    glutCreateWindow("Example 2.7.sphere.c: press SPACE & another key");

    glutKeyboardFunc(Key);
    glutReshapeFunc(Reshape); 
    glutDisplayFunc(display);
    glutIdleFunc(display);

    glutMainLoop();
}