Strange Attractors

var canvas = document.getElementById("canvas"); 
var ctx = canvas.getContext("2d"); 
var width = 800; 
var height = 800; 
var pixels = Array(width).fill(0).map(x => Array(height).fill(0.0)); 

//var a = -1.4, b = 1.6, c = 1.0, d = 0.7; 
//var a = 1.7, b = 1.7, c = 0.6, d = 1.2; 
//var a = -1.8, b = -2.0, c = -0.5, d = -0.9; 
var a = -1.4, b = 1.6, c = -1.0, d = 0.9; 
//var a = 1.5, b = -1.8, c = 1.6, d = 0.9; 

var x = 0, y = 0; 
var max = 0.0; 

// generate 
for (var i = 0; i < 40000000; ++i) 
{ 
   var x1 = Math.sin(a * y) + c * Math.cos(a * x); 
   var y1 = Math.sin(b * x) + d * Math.cos(b * y); 

   var m = Math.round((x1 + 2.5) * width / 5); 
   var n = Math.round((2.5 - y1) * height / 5); 
   var h = ++pixels[m][n]; 
   max = Math.max(max, h); 

   x = x1; 
   y = y1; 
} 

// draw 
for (var m = 0; m < width; ++m) 
{ 
   for (var n = 0; n < height; ++n) 
   { 
       var color = 2 * Math.round(Math.sqrt(pixels[m][n] / max) * 100.0); 
       color = Math.max(0, Math.min(color, 100)); 
       ctx.fillStyle = "hsl("+ 30 + "," + 100 + "%," + (100 - color) +"%)"; 
       ctx.fillRect(m, n, 1, 1); 
   } 
}