/*  fractalgl.c   using fractals to draw a tree */

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

static int w1W           = 600;
static int w1H           = 500;
static float height      = 80.0f;
static float width       = 20.0f;
static float left_alpha  =  2.0f;
static float right_alpha =  2.2f;
static float left_angle  = 20.0f;
static float right_angle = 26.0f;
static int level_in      = 14;
static float left_width_factor;
static float right_width_factor;
static float left_height_factor;
static float right_height_factor;
static int level; 
static float x, y, x1, y01;
static float turtle_x, turtle_y, turtle_r, turtle_theta;

static void turn(float angle);
static float point(float x1, float y01, float x2, float y2);
static void step();

static void drawbranch(float widthl, int x0, int y0, int x1, int y1)
{
  if(widthl < 1.5f)
  {
    glLineWidth(1.0);
    glBegin(GL_LINES);
      glVertex2f(x0, y0);
      glVertex2f(x1, y1);
    glEnd();
  }
  glLineWidth(widthl);
  glBegin(GL_LINES);
    glVertex2f(x0, y0);
    glVertex2f(x1, y1);
  glEnd();
  return;
}
  
static void generate(float x, float y, float widtht, float height,
                   float angle, int level)
{
  float x1, y01;
  
  turtle_x = x;
  turtle_y = y;
  turtle_r = height;
  step();
  x1 = turtle_x;
  y01 = turtle_y;
  level--;
  if(level<3)
  {
    glColor3f(0.0, 1.0, 0.0);
    drawbranch(widtht, (int)x, (int)y, (int)x1, (int)y01);
  }
  else
  {
    glColor3f(0.0, 0.0, 0.0);
    drawbranch(widtht, (int)x, (int)y, (int)x1, (int)y01);
  }
  if(level>0)
  {
    turtle_theta = point(x, y, x1, y01);
    turn(left_angle);
    generate(turtle_x, turtle_y, left_width_factor*widtht,
             left_height_factor*height, left_angle, level);
    turtle_theta = point(x, y, x1, y01);
    turn(-right_angle);
    generate(x1, y01, left_width_factor*widtht,
             left_height_factor*height, right_angle, level);
  }
} /* end generate */

static void turn(float angle)
{
  turtle_theta += angle;
} /* end turn */

static float point(float x1, float y01, float x2, float y2)
{
  float theta;
  
  if((x2-x1)==0.0)
  {
    if(y2>y01) theta=90.0f;
    else       theta=270.0f;
  }
  else
  {
    theta=atan((y2-y01)/(x2-x1))*57.295779f;
  }
  if(x1>x2) theta += 180.0f;
  return theta;
} /* end point */

static void step()
{
  turtle_x += turtle_r*cos(turtle_theta*0.017453292);
  turtle_y += turtle_r*sin(turtle_theta*0.017453292);
} /* end step */

static void display(void)
{
  /* clear window */
  glClear(GL_COLOR_BUFFER_BIT); 
  glLoadIdentity ();
  glColor3f(0.0, 0.0, 0.0);
  level = level_in;
  left_width_factor   = pow(2.0, -1.0/left_alpha);
  right_width_factor  = pow(2.0, -1.0/right_alpha);
  left_height_factor  = pow(2.0, -2.0/(3*left_alpha));
  right_height_factor = pow(2.0, -2.0/(3*right_alpha));

  x = (float)w1W/2.0f;
  y = (float)w1H/10.0f;

  x1 = x;
  y01 = y+height;
  drawbranch(width, (int)x, (int)y, (int)x1, (int)y01);
  turtle_r = height;
  turtle_theta = point(x, y, x1, y01);
  turtle_x = x;
  turtle_y = y;
  turn(left_angle);
  generate(x1, y01, left_width_factor*width,
           left_height_factor*height, left_angle, level);
  turtle_theta = point(x, y, x1, y01);
  turn(-right_angle);
  generate(x1, y01, left_width_factor*width,
           left_height_factor*height, right_angle, level);
  glFlush(); 
} /* end display */

/* This routine handles window resizes */
static void reshape(int w, int h)
{
  w1W = w;
  w1H = h;
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0.0, (float)w1W, 0.0, (float)w1H);
  glMatrixMode(GL_MODELVIEW);
  glViewport(0, 0, w1W, w1H);
  printf("reshape w1H=%d, w1H=%d \n", w1W, w1H);
} /* end reshape */

static void init()
{
  /* set clear color to white */
  glClearColor (1.0, 1.0, 1.0, 0.0);
  /* set fill  color to black */
  glColor3f(0.0, 0.0, 0.0);

  glMatrixMode (GL_PROJECTION);
  glLoadIdentity ();
  gluOrtho2D(0.0, (float)w1W, 0.0, (float)w1H);
  glMatrixMode (GL_MODELVIEW);
  glViewport(0, 0, w1W, w1H);
} /* end init */

int main(int argc, char* argv[])
{
  printf("fractalgl.c tree from \n");
  printf("height=%f, width=%f, left_alpha=%f, right_alpha=%f \n",
          height, width, left_alpha, right_alpha);
  printf("left_angle=%f, right_angle%f, level_in=%d \n",
          left_angle, right_angle, level_in);
  glutInit(&argc,argv);
  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);  
  glutInitWindowSize(w1W, w1H);
  glutInitWindowPosition(100,100); 
  glutCreateWindow(argv[0]); 
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  init();
  glutMainLoop();
  return 0;
} /* end main in fractalgl.c */