added a simple feedback example

Author: aceslowman

src/data/examples/en/20_3D/12_simple_feedback.js

@@ -0,0 +1,42 @@
+/*
+ * @name Simple Feedback
+ * @arialabel An example of a simple feedback effect using two buffers.
+ * @description A simple feedback effect can be achieved through WEBGL mode and two graphics buffers.
+ */
+
+let pg, swap;
+
+function setup() {
+  createCanvas(710, 400);
+
+  // this will hold our main graphic
+  pg = createGraphics(710, 400, WEBGL);
+  // this will hold the previous frame
+  swap = createGraphics(710, 400, WEBGL);
+}
+
+function draw() {
+  // draw the previous frame
+  pg.texture(swap);
+  pg.noStroke();  
+  pg.plane(width, height);
+
+  // draw our circle graphic on top
+  pg.fill(255);
+  pg.ellipse(Math.sin(millis()/200)*5, Math.cos(millis()/200)*5, 150, 150);
+
+  // draw a slightly scaled up copy of the texture
+  swap.push();
+  swap.scale(1.1, 1.1);
+  swap.texture(pg);
+  swap.noStroke();
+  swap.plane(width, height);
+  swap.pop();
+
+  // an opaque rectangle is drawn over top to control the feedback decay
+  swap.fill(0, 50);
+  swap.rect(-width / 2, -height / 2, width, height);
+
+  // draw the output to the screen
+  image(swap, 0, 0);
+}