createGraphics ?

var c2; // global second graphics context

​

function setup() {

 createCanvas(500,500); // default graphics context

 c2 = createGraphics(500,500); // second graphics context, same size

 c2.background(255);

 c2.ellipse(100,100,50,50); // draw an ellipse on the second screen

​

}

​

function draw() {

 image(c2,0,0); // render the second screen

 noFill();

 rect(0,0,width-1,height-1); // put a bounding rectangle around the default screen

 ellipse(100,100,50,50); // draw same ellipse on the default screen

 // two ellipses should be identical, but they're not (at least on my computer

 // which is a surface pro 4), the c2 context seems to be blown up somehow. 

}

​

// click to place garish circles on second graphics context, they don't appear

// at the proper location

function mouseClicked() {

 c2.stroke(color(255,0,0));

 c2.fill(color(0,255,0));

 c2.ellipse(mouseX,mouseY,10,10);

 print(mouseX + ", " + mouseY);

}