/* Example 1.5.circle.c: animation and circle 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[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 subdivideCircle(int radius, float *v1, float *v2, int depth)
{
	float v11[3], v22[3], v00[3] = {0, 0, 0}, v12[3];
	int i;

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

		for (i=0; i<3; i++) {
			v11[i] = v1[i]*radius;
			v22[i] = v2[i]*radius;
		}
		drawtriangle(v11, v22, v00);

		return;
	}
		
	v12[0] = v1[0]+v2[0]; 
	v12[1] = v1[1]+v2[1];
	v12[2] = v1[2]+v2[2];


	normalize(v12);

	subdivideCircle(radius, v1, v12, depth - 1);
	subdivideCircle(radius, v12, v2, depth - 1);
}


void drawCircle(int circleRadius)
// draw a circle with center at the origin in xy plane
{

	subdivideCircle(circleRadius, vdata[0], vdata[1], depth);
	subdivideCircle(circleRadius, vdata[1], vdata[2], depth);
	subdivideCircle(circleRadius, vdata[2], vdata[3], depth);
	subdivideCircle(circleRadius, vdata[3], vdata[0], depth);	
}


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

	circleRadius+=cnt;

	glClear(GL_COLOR_BUFFER_BIT);
	drawCircle(circleRadius);

	glutSwapBuffers();
}



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

	Width = w; Height = h; 

    glViewport (0, 0, Width, Height);

    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    glOrtho(-Width/2, Width/2, -Height/2, Height/2, -1.0, 1.0); 
}



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 1.5.circle.c: press SPACE & another key");

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

    glutMainLoop();
}