viz7

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+---
+title: >-
+    Visualization 7
+description: >-
+    Feedback Loop.
+series: viz
+tags: tech art
+---
+
+<script type="text/javascript">
+
+function randn(n) {
+    return Math.floor(Math.random() * n);
+}
+
+const w = 100;
+const h = 60;
+
+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 UniverseState {
+  constructor(layers) {
+    this.tick = 0;
+    this.layers = layers;
+  }
+
+  neighboringLayers(layerIndex) {
+    const prevIndex = layerIndex-1;
+    const prev = prevIndex < 0 ? null : this.layers[prevIndex];
+
+    const nextIndex = layerIndex+1;
+    const next = nextIndex >= this.layers.length ? null : this.layers[nextIndex];
+
+    return [prev, next];
+  }
+}
+
+const defaultKnobs = {
+  maxNewElsPerTick: 10,
+  ageOfDeath: 30,
+  drift: 30,
+  neighborScalar: 0,
+  prevLayerScalar: 0,
+  prevLayerLikenessScalar: 0,
+  nextLayerScalar: 0,
+  nextLayerLikenessScalar: 0,
+  chaos: 0,
+};
+
+class Layer {
+  constructor(className, newEl, knobs = {}) {
+    this.className = className;
+    this.els = {};
+    this.diff = {};
+    this.newEl = newEl;
+    this.knobs = { ...defaultKnobs, ...knobs };
+  }
+
+  _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, thisLayerIndex) {
+    // 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) {
+      const newEl = this.newEl(this, [])
+      newEl.tick = state.tick;
+      this.set([w/2, h/2], newEl);
+      return;
+    }
+
+    let newEls = 0;
+    for (const el of allEls) {
+      const nCoord = randEmptyNeighboringCoord(this, el.coord);
+      if (!nCoord) continue; // el has no empty neighboring spots
+
+      const newEl = this.newEl(this, neighboringElsOf(this, nCoord))
+      newEl.tick = state.tick;
+      this.set(nCoord, newEl);
+
+      newEls++;
+      if (newEls >= this.knobs.maxNewElsPerTick) break;
+    }
+
+    const calcLayerBonus = (el, layer, scalar, likenessScalar) => {
+        if (!layer) return 0;
+        const nEls = neighboringElsOf(layer, el.coord, true)
+
+        const likeness = nEls.reduce((likeness, nEl) => {
+            const diff = Math.abs(nEl.c - el.c);
+            return likeness + Math.max(diff, Math.abs(1 - diff));
+        }, 0);
+
+        return (nEls.length * scalar) + (likeness * likenessScalar);
+    };
+
+    const [prevLayer, nextLayer] = state.neighboringLayers(thisLayerIndex);
+
+    for (const el of allEls) {
+      const age = state.tick - el.tick;
+      const neighborBonus = neighboringElsOf(this, el.coord).length * this.knobs.neighborScalar;
+      const prevLayerBonus = calcLayerBonus(el, prevLayer, this.knobs.prevLayerScalar, this.knobs.prevLayerLikenessScalar);
+      const nextLayerBonus = calcLayerBonus(el, nextLayer, this.knobs.nextLayerScalar, this.knobs.nextLayerLikenessScalar);
+      const chaos = (this.chaos > 0) ? randn(this.knobs.chaos) : 0;
+
+      if (age - neighborBonus - prevLayerBonus - nextLayerBonus + chaos >= this.knobs.ageOfDeath) {
+        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, includeCoord = false) {
+  const neighboringEls = [];
+
+  const neighboringCoords = neighborsOf(coord);
+  if (includeCoord) neighboringCoords.push(coord);
+
+  for (const nCoord of neighboringCoords) {
+    const el = layer.get(nCoord);
+    if (el) neighboringEls.push(el);
+  }
+  return neighboringEls;
+}
+
+function newEl(h, l) {
+  return {
+    h: h,
+    s: "100%",
+    l: l,
+    c: h / 360, // c is used to compare the element to others
+  };
+}
+
+function mkNewEl(l) {
+  return (layer, nEls) => {
+    const s = "100%";
+    if (nEls.length == 0) {
+      const h = randn(360);
+      return newEl(h, 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() * layer.knobs.drift * 2) - layer.knobs.drift;
+    h = (h + 360) % 360;
+
+    return newEl(h, l);
+  }
+}
+
+class Universe {
+  constructor(canvasesByClass, layers) {
+    this.canvasesByClass = canvasesByClass;
+    this.state = new UniverseState(layers);
+  }
+
+  update() {
+    this.state.tick++;
+    let prevLayer;
+    this.state.layers.forEach((layer, i) => {
+        layer.update(this.state, i);
+        prevLayer = layer;
+    });
+  }
+
+  draw() {
+    this.state.layers.forEach((layer) => {
+      if (!this.canvasesByClass[layer.className]) return;
+      this.canvasesByClass[layer.className].forEach((canvas) => {
+        layer.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">
+    <h3>Bottom Layer</h3>
+    <div class="canvasContainer"><canvas class="layer1"></canvas></div>
+    <div class="layer1 layerParams">
+        <label>Max New Elements Per Tick</label><input type="text" param="maxNewElsPerTick" />
+        <label>Color Drift</label><input type="text" param="drift" />
+        <label>Age of Death</label><input type="text" param="ageOfDeath" />
+        <label>Neighbor Scalar</label><input type="text" param="neighborScalar" />
+        <label>Top Layer Neighbor Scalar</label><input type="text" param="nextLayerScalar" />
+        <label>Top Layer Neighbor Likeness Scalar</label><input type="text" param="nextLayerLikenessScalar" />
+    </div>
+  </div>
+
+  <div class="columns six">
+    <h3>Top Layer</h3>
+    <div class="canvasContainer"><canvas class="layer2"></canvas></div>
+    <div class="layer2 layerParams">
+        <label>Max New Elements Per Tick</label><input type="text" param="maxNewElsPerTick" />
+        <label>Color Drift</label><input type="text" param="drift" />
+        <label>Age of Death</label><input type="text" param="ageOfDeath" />
+        <label>Neighbor Scalar</label><input type="text" param="neighborScalar" />
+        <label>Bottom Layer Neighbor Scalar</label><input type="text" param="prevLayerScalar" />
+        <label>Bottom Layer Neighbor Likeness Scalar</label><input type="text" param="prevLayerLikenessScalar" />
+    </div>
+  </div>
+
+</div>
+
+Once again, this visualization iterates upon the previous. In the last one the
+top layer was able to "see" the bottom, and was therefore able to bolster or
+penalize its own elements which were on or near bottom layer elements, but not
+vice-versa. This time both layers can see each other, and the "Layer Neighbor
+Scalar" can be used to adjust lifetime of elements which are on/near elements of
+the neighboring layer.
+
+By default, the bottom layer has a high affinity to the top, and the top layer
+has a some (but not as much) affinity in return.
+
+Another addition is the "likeness" scalar. Likeness is defined as the degree to
+which one element is like another. In this visualization likeness is determined
+by color. The "Layer Neighbor Likeness Scalar" adjusts the lifetime of elements
+based on how like they are to nearby elements on the neighboring layer.
+
+By default, the top layer has a high affinity for the bottom's color, but the
+bottom doesn't care about the top's color at all (and so its color will drift
+aimlessly).
+
+And finally "Color Drift" can be used to adjust the degree to which the color of
+new elements can diverge from its parents. This has always been hardcoded, but
+can now be adjusted separately across the different layers.
+
+In the default configuration the top layer will (eventually) converge to roughly
+match the bottom both in shape and color. When I first implemented the likeness
+scaling I thought it was broken, because the top would never converge to the
+bottom's color.
+
+What I eventually realized was that the top must have a higher color drift than
+the bottom in order for it to do so, otherwise the top would always be playing
+catchup. However, if the drift difference is _too_ high then the top layer
+becomes chaos and also doesn't really follow the color of the bottom. A
+difference of 10 (degrees out of 360) is seemingly enough.
+
+<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 layers = [
+
+  new Layer("layer1", mkNewEl("90%"), {
+    maxNewElsPerTick: 2,
+    ageOfDeath: 30,
+    drift: 40,
+    neighborScalar: 50,
+    nextLayerScalar: 20,
+  }),
+
+  new Layer("layer2", mkNewEl("50%", ), {
+    maxNewElsPerTick: 15,
+    ageOfDeath: 1,
+    drift: 50,
+    neighborScalar: 5,
+    prevLayerScalar: 5,
+    prevLayerLikenessScalar: 20,
+  }),
+
+];
+
+for (const layer of layers) {
+    document.querySelectorAll(`.${layer.className}.layerParams > input`).forEach((input) => {
+        const param = input.getAttribute("param");
+
+        // pre-fill input values
+        input.value = layer.knobs[param];
+
+        input.onchange = () => {
+            console.log(`setting ${layer.className}.${param} to ${input.value}`);
+            layer.knobs[param] = input.value;
+        };
+    });
+}
+
+const universe = new Universe(canvasesByClass, layers);
+
+const requestAnimationFrame =
+  window.requestAnimationFrame ||
+  window.mozRequestAnimationFrame ||
+  window.webkitRequestAnimationFrame ||
+  window.msRequestAnimationFrame;
+
+function doTick() {
+  universe.update();
+  universe.draw();
+  requestAnimationFrame(doTick);
+}
+
+doTick();
+
+</script>