// String art, Version 1
// Start with a simple setup
// to draw lines...

// Version 1: Vary the stroke color

float angle;
float radius;
float cx, cy;
float x1, y1, x2, y2;
float strokeColor;      

float strokeDelta;  // Define this (V1)

void setup() {
  size(500, 500);
  smooth();
  background(255);

  // Initial settings
  cx = width/2;
  cy = height/2;
  radius = width/2;
  angle = 0; // degrees 
  strokeColor = 0;

  strokeDelta = 1;    // stroke color will change by 1
} // setup

void draw() {

  angle = angle - 3;
  float theta = radians(angle);

  // compute the end points of line
  x1 = cx + radius * cos(theta);
  y1 = cy + radius * sin(theta);

  x2 = cx + radius * cos(theta+PI);
  y2 = cy + radius * sin(theta+PI);

  // Draw the line
  // Modify stroke color properties (V1)
  strokeColor = strokeColor + strokeDelta;
  if (strokeColor > 255 || strokeColor < 0) {
    strokeDelta = strokeDelta * -1;
  }

  stroke(strokeColor);
  strokeWeight(1);
  line(x1, y1, x2, y2);
} // draw()