/* Example 2.5.cone: draw a cone 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=5, circleRadius=200, cnt=1; 


static float vdata[4][3] = {
	{1.0, 0.0, 0.0}, {0.0, 1.0, 0.0}, 
	{-1.0, 0.0, 0.0}, {0.0, -1.0, 0.0}
};


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 subdivideCone(float *v1, float *v2, int depth)
{
	float v0[3] = {0, 0, 0}, v12[3];
	int i;

	if (depth == 0) {
		glColor3f(v1[0]*v1[0], v1[1]*v1[1], v1[2]*v1[2]);

		drawtriangle(v1, v2, v0); // bottom cover of the cone

		v0[2] = 1; // height of the cone, the tip on z axis
		drawtriangle(v1, v2, v0); // side cover of the cone

		return;
	}
		
	for (i=0; i<3; i++) 
		v12[i] = v1[i]+v2[i]; 

	normalize(v12);

	subdivideCone(v1, v12, depth - 1);
	subdivideCone(v12, v2, depth - 1);
}


void drawCone(void)
// draw a unit cone with center at the origin and bottom in xy plane
{
	subdivideCone(vdata[0], vdata[1], depth);
	subdivideCone(vdata[1], vdata[2], depth);
	subdivideCone(vdata[2], vdata[3], depth);
	subdivideCone(vdata[3], vdata[0], depth);	
}


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

	circleRadius+=cnt;

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


	glRotatef(1.1, 1, 0, 0); // rotate 1.1 degree alone x axis
	glPushMatrix();
		glScaled(circleRadius, circleRadius, circleRadius);
		drawCone();
	glPopMatrix();

	glutSwapBuffers();
}



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

	// enable zbuffer (depthbuffer) for hidden-surface removal
	glEnable(GL_DEPTH_TEST);

	Width = w; Height = h; 

    glViewport (0, 0, Width, Height);

    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
	// make sure the cone is within the viewing volume
    glOrtho(-Width/2, Width/2, -Height/2, Height/2, -Width/2, Width/2); 
 
	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 2.5.cone.c: press SPACE & another key");

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

    glutMainLoop();
}