// This example shows the basic
// structure of most Processing programs:
// using "setup" and "draw". This program
// resembles the previous example very much.
// In contrast however, it never stops
// drawing lines.
//
// Example I.4

float P1x, P1y;
float P2x, P2y;
float P3x, P3y;
float P4x, P4y;
float P5x, P5y;
float P6x, P6y;
float P7x, P7y;
float P8x, P8y;

int xint, yint, x2int, y2int;
float x, y;
float x2, y2;
float Aang = 0.0;
float Bang, Cang;
float Aang2, Bang2, Cang2;
float totang;
float d1, d2, d3;
float a, b, c;
float radius = 20;
int center = 250;

// Everything inside this function is done
// once, at the start of program execution.
void setup() {
  size(500, 500);
  background(102);
}

// law of sines
// sin(Aang)/a == sin(Bang)/b
// Aang = asin((a * sin(Bang))/b)

// law of cosines
// sq(c) == sq(a) + sq(b) - 2*a*b*cos(Cang)
// 2*a*b*cos(Cang) == sq(a) + sq(b) - sq(c)
// cos(Cang) == (sq(a) + sq(b) - sq(c))/(2*a*b)
// Cang == acos((sq(a) + sq(b) - sq(c))/(2*a*b))
//


// Everything inside this function is done
// continuously and without stopping, after
// setup() is done.
// In this example it keeps on drawing 
// lines with an orientation (a) that
// changes slowly towards zero degrees.
void draw() {
  background(102); // refreshes the screen
  P1x = (float) (center);
  P1y = (float) (center);
  ellipseMode (CENTER);
  ellipse (P1x, P1y, 2*radius, 2*radius);
  P2x =  P1x + (radius * cos(Aang));
  P2y =  P1y + (radius * sin(Aang));
  line(P1x, P1y, P2x, P2y); 
  P3x =  (P1x + 80);
  P3y =  P1y;
  line(P1x, P1y, P3x, P3y);
  line(P2x, P2y, P3x, P3y); 
  // Now compute P4
  d1 = dist(P2x, P2y, P3x, P3y); 
  Cang = acos((sq(radius) + sq(d1) - sq(80))/(2*radius*d1));
  Bang = PI - (Aang + Cang); 
	// this is the angle between the length P1 P3 and P2 P3 
  if (Aang > PI) Bang = PI - (((2*PI) - Aang) + Cang); // Bang will be 
	// above the horizontal.
  Cang2 = acos((sq(d1) + sq(60) - sq(70))/(2*d1*60));
  totang = Bang + Cang2; 
  if (Aang > PI) totang = Cang2 - Bang; // after PI, need to subtract Bang
  P4x = ((P3x) - (60 * cos(totang)));
  P4y = (int) ((P3y ) + (60 * sin(totang))); 
  d2 = dist(P4x, P4y, P2x, P2y);
  if ((d2 <= 71) && (d2 >= 69)) Aang += PI/180;
  line(P4x, P4y, P2x, P2y);
  line(P4x, P4y, P3x, P3y);
  if(Aang >= 2 * PI) Aang = Aang - (2*PI);
}

void mousePressed() 
{
  loop();
}