nature-of-code · ant-fugue · Apr 28, 2021
diff --git a/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/CA.js b/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/CA.js
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+class CA {
+  constructor() {
+    // the width of each cell
+    this.w = 10;
+
+    // all cells start with state 0, except the center cell has state 1
+    this.cells = new Array(width / this.w).fill(0);
+    this.cells[this.cells.length / 2] = 1;
+
+    // keep track of generations
+    this.generation = 0;
+
+    // rule 90 in Wolfram's CA
+    this.ruleSet = [0, 1, 0, 1, 1, 0, 1, 0];
+  }
+
+  generate() {
+    // an array to store the state for the next generation
+    let nextGen = new Array(this.cells.length).fill(0);
+
+    // update generation
+    for (let i = 1; i < this.cells.length - 1; i++) {
+      // look at the states from the current array
+      let left = this.cells[i - 1];
+      let middle = this.cells[i];
+      let right = this.cells[i + 1];
+
+      // create a new generation from a rule
+      nextGen[i] = this.rules(left, middle, right);
+
+      // the new generation becomes the current generation
+    }
+    this.cells = nextGen;
+    this.generation++;
+  }
+
+  // look up a new state from the ruleset
+  rules(a, b, c) {
+    // join three bits into a string
+    let s = "" + a + b + c;
+
+    // translate binary into a index in the ruleset
+    let index = parseInt(s, 2);
+
+    // return a new state from the rule in the ruleset
+    return this.ruleSet[index];
+  }
+
+  display() {
+    // call restart() when the last generation reaches the edge of the canvas
+    if (this.generation * this.w >= height) {
+      this.restart();
+    }
+    for (let i = 0; i < this.cells.length; i++) {
+      // 0 -> white, 1 -> black
+      if (this.cells[i] === 1) fill(0);
+      else fill(255);
+      // display each generation
+      rect(i * this.w, this.generation * this.w, this.w, this.w);
+    }
+  }
+  // randomize the states of cells and reset generation counter
+  restart() {
+    this.cells = new Array(width / this.w)
+      .fill(0)
+      .map((elem) => Math.round(Math.random()));
+    this.generation = 0;
+  }
+}
diff --git a/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/index.html b/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/index.html
@@ -0,0 +1,13 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.9.0/p5.min.js"></script>
+    <script src="https://cdnjs.cloudflare.com/ajax/libs/p5.js/0.9.0/addons/p5.dom.min.js"></script>
+    <meta charset="utf-8" />
+  </head>
+
+  <body>
+    <script src="CA.js"></script>
+    <script src="sketch.js"></script>
+  </body>
+</html>
diff --git a/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/sketch.js b/chp07_CA/Exercise_7_02_WolframCA_randomized_initial_states/sketch.js
@@ -0,0 +1,13 @@
+let ca;
+
+function setup() {
+  frameRate(20);
+  createCanvas(400, 400);
+  ca = new CA();
+}
+
+function draw() {
+  ca.generate();
+  ca.rules();
+  ca.display();
+}