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+---
+title: >-
+    Visualization 5
+description: >-
+    TODO
+series: viz
+tags: tech art
+---
+
+<script type="text/javascript">
+
+function randn(n) {
+    return Math.floor(Math.random() * n);
+}
+
+const w = 100;
+const h = 50;
+
+const maxNewElsPerTick = 10;
+const deathThresh = 10;
+
+class Canvas {
+  constructor(canvasDOM) {
+    this.dom = canvasDOM;
+    this.ctx = canvasDOM.getContext("2d");
+
+    // expand canvas element's width to match parent.
+    this.dom.width = this.dom.parentElement.offsetWidth;
+
+    // rectSize must be an even number or the pixels don't display nicely.
+    this.rectSize = Math.floor(this.dom.width / w /2) * 2;
+
+    this.dom.width = w * this.rectSize;
+    this.dom.height = h * this.rectSize;
+  }
+
+  rectSize() {
+    return Math.floor(this.dom.width / w);
+  }
+}
+
+class Layer {
+  constructor(newEl) {
+    this.els = {};
+    this.diff = {};
+    this.newEl = newEl;
+  }
+
+  _normCoord(coord) {
+    if (typeof coord !== 'string') coord = JSON.stringify(coord);
+    return coord;
+  }
+
+  get(coord) {
+    return this.els[this._normCoord(coord)];
+  }
+
+  getAll() {
+    return Object.values(this.els);
+  }
+
+  set(coord, el) {
+    this.diff[this._normCoord(coord)] = {action: "set", coord: coord, ...el};
+  }
+
+  unset(coord) {
+    this.diff[this._normCoord(coord)] = {action: "unset"};
+  }
+
+  applyDiff() {
+    for (const coordStr in this.diff) {
+      const el = this.diff[coordStr];
+      delete this.diff[coordStr];
+
+      if (el.action == "set") {
+        delete el.action;
+        this.els[coordStr] = el;
+      } else {
+        delete this.els[coordStr];
+      }
+    }
+  }
+
+  update(state) {
+    // Apply diff from previous update first. The diff can't be applied last
+    // because it needs to be present during the draw phase.
+    this.applyDiff();
+
+    const allEls = this.getAll().sort(() => Math.random() - 0.5);
+
+    if (allEls.length == 0) {
+      this.set([w/2, h/2], this.newEl([]));
+    }
+
+    let newEls = 0;
+    for (const el of allEls) {
+      const nCoord = randEmptyNeighboringCoord(this, el.coord);
+      if (!nCoord) continue; // el has no empty neighboring spots
+
+      const nEl = this.newEl(neighboringElsOf(this, nCoord))
+      nEl.tick = state.tick;
+      this.set(nCoord, nEl);
+
+      newEls++;
+      if (newEls >= maxNewElsPerTick) break;
+    }
+
+    for (const el of allEls) {
+      const nEls = neighboringElsOf(this, el.coord);
+      if (state.tick - el.tick - (nEls.length * deathThresh) >= deathThresh) this.unset(el.coord);
+    }
+}
+
+  draw(canvas) {
+    for (const coordStr in this.diff) {
+      const el = this.diff[coordStr];
+      const coord = JSON.parse(coordStr);
+
+      if (el.action == "set") {
+        canvas.ctx.fillStyle = `hsl(${el.h}, ${el.s}, ${el.l})`;
+        canvas.ctx.fillRect(
+          coord[0]*canvas.rectSize, coord[1]*canvas.rectSize,
+          canvas.rectSize, canvas.rectSize,
+        );
+
+      } else {
+        canvas.ctx.clearRect(
+          coord[0]*canvas.rectSize, coord[1]*canvas.rectSize,
+          canvas.rectSize, canvas.rectSize,
+        );
+      }
+    }
+  }
+}
+
+const neighbors = [
+    [-1, -1],   [0, -1],   [1, -1],
+    [-1, 0], /* [0, 0], */ [1, 0],
+    [-1, 1],    [0, 1],    [1, 1],
+];
+
+function neighborsOf(coord) {
+  return neighbors.map((n) => {
+    let nX = coord[0]+n[0];
+    let nY = coord[1]+n[1];
+    nX = (nX + w) % w;
+    nY = (nY + h) % h;
+    return [nX, nY];
+  });
+}
+
+function randEmptyNeighboringCoord(layer, coord) {
+  const neighbors = neighborsOf(coord).sort(() => Math.random() - 0.5);
+  for (const nCoord of neighbors) {
+    if (!layer.get(nCoord)) return nCoord;
+  }
+  return null;
+}
+
+function neighboringElsOf(layer, coord) {
+  const neighboringEls = [];
+  for (const nCoord of neighborsOf(coord)) {
+    const el = layer.get(nCoord);
+    if (el) neighboringEls.push(el);
+  }
+  return neighboringEls;
+}
+
+const drift = 30;
+function mkNewEl(l) {
+  return (nEls) => {
+    const s = "100%";
+    if (nEls.length == 0) {
+      return {
+        h: randn(360),
+        s: s,
+        l: l,
+      };
+    }
+
+    // for each h (which can be considered as degrees around a circle) break the h
+    // down into x and y vectors, and add those up separately. Then find the angle
+    // between those two resulting vectors, and that's the "average" h value.
+    let x = 0;
+    let y = 0;
+    nEls.forEach((el) => {
+      const hRad = el.h * Math.PI / 180;
+      x += Math.cos(hRad);
+      y += Math.sin(hRad);
+    });
+
+    let h = Math.atan2(y, x);
+    h = h / Math.PI * 180;
+
+    // apply some random drift, normalize
+    h += (Math.random() * drift * 2) - drift;
+    h = (h + 360) % 360;
+
+    return {
+      h: h,
+      s: s,
+      l: l,
+    };
+  }
+}
+
+class Universe {
+  constructor(canvasesByClass, layersByClass) {
+    this.canvasesByClass = canvasesByClass;
+    this.state = {
+      tick: 0,
+      layers: layersByClass,
+    };
+  }
+
+  update() {
+    this.state.tick++;
+    Object.values(this.state.layers).forEach((layer) => layer.update(this.state));
+  }
+
+  draw() {
+    for (const layerName in this.state.layers) {
+      if (!this.canvasesByClass[layerName]) return;
+      this.canvasesByClass[layerName].forEach((canvas) => {
+        this.state.layers[layerName].draw(canvas);
+      });
+    }
+  }
+}
+
+</script>
+
+<style>
+
+.canvasContainer {
+  display: grid;
+  margin-bottom: 2rem;
+  text-align: center;
+}
+
+canvas {
+  border: 1px dashed #AAA;
+  width: 100%;
+  grid-area: 1/1/2/2;
+}
+
+</style>
+
+<div class="canvasContainer">
+  <canvas class="layer1"></canvas>
+  <canvas class="layer2"></canvas>
+</div>
+
+<div class="row">
+  <div class="columns six">
+    <div class="canvasContainer"><canvas class="layer1"></canvas></div>
+  </div>
+  <div class="columns six">
+    <div class="canvasContainer"><canvas class="layer2"></canvas></div>
+  </div>
+</div>
+
+This visualization combines two distinct layers, each of them borrowing their
+behavior from [Visualization 4][viz4]. Neither layer has any effect on the
+other, one is merely super-imposed on top of the other in the top canvas. You
+can see each layer individually in the two lower canvases.
+
+Despite their not affecting each other, the code is set up so that each layer
+_could_ be affected by the other. This will likely be explored more in a future
+post.
+
+[viz4]: {% post_url 2021-05-26-viz-4 %}
+
+<script>
+
+const canvasesByClass = {};
+[...document.getElementsByTagName("canvas")].forEach((canvasDOM) => {
+
+  const canvas = new Canvas(canvasDOM);
+  canvasDOM.classList.forEach((name) => {
+    if (!canvasesByClass[name]) canvasesByClass[name] = [];
+    canvasesByClass[name].push(canvas);
+  })
+});
+
+
+const universe = new Universe(canvasesByClass, {
+  "layer1": new Layer(mkNewEl("90%")),
+  "layer2": new Layer(mkNewEl("50%")),
+});
+
+const requestAnimationFrame =
+  window.requestAnimationFrame ||
+  window.mozRequestAnimationFrame ||
+  window.webkitRequestAnimationFrame ||
+  window.msRequestAnimationFrame;
+
+function doTick() {
+  universe.update();
+  universe.draw();
+  requestAnimationFrame(doTick);
+}
+
+doTick();
+
+</script>