guilloche.jsx

// get the curent document
var doc_ref = doc = app.activeDocument;

// get current artboard and save width/height for use in sizing the guilloche
var currentArtboard = doc_ref.artboards[doc_ref.artboards.getActiveArtboardIndex()],
    size = {
      x: Math.floor(Math.abs( currentArtboard.artboardRect[2] )), 
      y: Math.floor(Math.abs( currentArtboard.artboardRect[3] ))
    },
    halfSize = {x: size.x / 2, y: size.y / 2};


// CONFIG ZONE - PLAY AROUND

// array of "good looking" guilloche keys. script chooses one at random
var keys = [50, 71, 75, 76, 100, 112, 152, 200, 269, 270, 279, 284, 292, 295, 300],
    guilloche_key = keys[ Math.floor( Math.random() * keys.length ) ];

// Guilloche rendering opts - have fun    
var factor = 0.426;
var guillocheOptions = {
  majorR: (size.x - 250),
	minorR: (size.x - 250)  * factor,
	angleMultiplier: guilloche_key,
  radiusEffectConstant: 250,
  steps: 1500,
  centerPoint: halfSize
};

// Line Style Configuration   
var lineStyleConfig = {
  stroked: true,
  filled: true,
  opacity: 25,
  strokeWidth: 0.2 // width in points  
};


// utility function for drawing a line
function draw_line(x1, y1, x2, y2){    
  newPath = doc_ref.pathItems.add(); 
  newPath.stroked = lineStyleConfig.stroked;
  newPath.filled = lineStyleConfig.filled;
  newPath.opacity = lineStyleConfig.opacity;
  newPath.strokeWidth = lineStyleConfig.strokeWidth;
  newPath.setEntirePath([[x1,-1*y1],[x2,-1*y2]]);
}

// here's where we actually draw the guilloche
var guilloche = function(){
	var	diff = guillocheOptions.majorR - guillocheOptions.minorR,
			s = diff / guillocheOptions.minorR,
			theta = 0,
			radiusEffect = guillocheOptions.radiusEffectConstant + guillocheOptions.minorR,        
			oldX, oldY;
			
	for (var i = guillocheOptions.steps; i--;) {
		var new_theta = guillocheOptions.angleMultiplier * theta,
			  x = diff * Math.sin(new_theta) + radiusEffect * Math.sin(new_theta * s) + (guillocheOptions.centerPoint.x),
			  y = diff * Math.cos(new_theta) - radiusEffect * Math.cos(new_theta * s) + (guillocheOptions.centerPoint.y);
			
		theta += Math.PI * 4 / guillocheOptions.steps;
		
		if (oldX)
      draw_line(oldX, oldY, x, y);
		
		oldX = x;
		oldY = y;
	}

};

// do it
guilloche();