Create Graphics

/**
 * Create Graphics. 
 * 
 * The createGraphics() function creates an object from 
 * the PGraphics class. PGraphics is the main graphics and 
 * rendering context for Processing. The beginDraw() method 
 * is necessary to prepare for drawing and endDraw() is
 * necessary to finish. Use this class if you need to draw 
 * into an off-screen graphics buffer or to maintain two 
 * drawing surfaces with different properties.
 */

PGraphics* pg;

void setup() {
    size(640, 360);
    pg = createGraphics(400, 200);
}

void draw() {
    fill(0, 12);
    rect(0, 0, width, height);

    fill(255);
    noStroke();
    ellipse(mouseX, mouseY, 60, 60);

    pg->beginDraw();
    pg->background(51);
    pg->noFill();
    pg->stroke(255);
    pg->ellipse(mouseX - 120, mouseY - 60, 60, 60);
    pg->endDraw();

    // Draw the offscreen buffer to the screen with image() 
    image(pg, 120, 60);
}