feat: implement blue noise generation for initial creature positions

static/index.js

@@ -6,6 +6,7 @@ const FRAME_RATE = 6; // in FPS
 const FRAME_DELAY = 1 / FRAME_RATE * 1000; // in ms
 const DEFAULT_SPRITE_SHEET_COUNT = 1; // number of default sprite sheets
 const WALK_SIZE = 8; // magnitude of position change, in px
+const MAX_RETRIES = 10;
 
 /**
  * Enum of directions
@@ -274,6 +275,120 @@ const isBetween = (val, min, max) => {
     return val >= min && val < max;
 }
 
+/**
+ * Generate an array of n vec2's such that all vectors lie in
+ * [left, left + width) x [top, top + height) and are at least radius
+ * distance away from all other points.
+ * This function uses almost (but not quite)
+ * [the poisson disk sampling method]{@link https://a5huynh.github.io/posts/2019/poisson-disk-sampling/}
+ * insofar that instead of generating points in an annulus around a seed,
+ * it generates points anywhere else in the bounds.
+ * @param {number} n the number of points to generate
+ * @param {number} radius the minimum distance between points
+ * @param {number} left x lower bound of points
+ * @param {number} top y lower bound of points
+ * @param {number} width x width of bounds
+ * @param {number} height y width of bounds
+ * @param {number=} maxRetries maximum number of generation attemps before giving up
+ * @return {Array<vec2>}
+ */
+const generateBlueNoise = (n, radius, left, top, width, height, maxRetries = MAX_RETRIES) => {
+    const gridCellSize = radius / Math.sqrt(2);
+    const gridWidth = Math.ceil(width / gridCellSize);
+    const gridHeight = Math.ceil(height / gridCellSize);
+    const grid = /** @type {Array<Array<vec2|undefined>>} */ [...Array(gridHeight)].map(() => Array(gridWidth));
+
+    /**
+     * @param {vec2} point
+     * @return {vec2}
+     */
+    const getSamplePoint = (point) => {
+        const randomX = Math.random() * (width - 2 * radius);
+        const randomY = Math.random() * (height - 2 * radius);
+
+        const samplePointX = left + (
+            randomX < (point.at(0) - radius) ? randomX : randomX + 2 * radius
+        )
+        const samplePointY = top + (
+            randomY < (point.at(1) - radius) ? randomY : randomY + 2 * radius
+        )
+
+        return [samplePointX, samplePointY];
+    }
+
+    /**
+     * @param {vec2} point
+     * @return {void}
+     */
+    const insertPointIntoGrid = (point) => {
+        const indexX = Math.floor((point.at(0) - left) / gridCellSize);
+        const indexY = Math.floor((point.at(1) - top) / gridCellSize);
+
+        grid[indexY][indexX] = point;
+    }
+
+    const areValid = (point1, point2) => {
+        const deltaX = point1.at(0) - point2.at(0);
+        const deltaY = point1.at(1) - point2.at(1);
+        return (deltaX * deltaX + deltaY * deltaY) > (radius * radius)
+    }
+
+    /**
+     * @param {vec2} point
+     * @return {boolean}
+     */
+    const isValidPoint = (point) => {
+        const indexX = Math.floor((point.at(0) - left) / gridCellSize);
+        const indexY = Math.floor((point.at(1) - top) / gridCellSize);
+
+        const testPoints = [
+            [indexX - 1, indexY - 1], [indexX, indexY - 1], [indexX + 1, indexY - 1],
+            [indexX - 1, indexY],     [indexX, indexY],     [indexX + 1, indexY],
+            [indexX - 1, indexY + 1], [indexX, indexY + 1], [indexX + 1, indexY + 1],
+        ]
+            .filter((indices) => (
+                indices.at(0) >= 0 && indices.at(1) >= 0 && indices.at(0) < gridWidth && indices.at(1) < gridHeight
+            ))
+            .map((indices) => grid[indices.at(1)][indices.at(0)])
+            .filter((point) => point !== undefined);
+
+        return testPoints.every((testPoint) => areValid(point, testPoint))
+    }
+
+    // initialize
+    const initialPoint = [
+        left + width / 2, top + height / 2,
+    ]
+    insertPointIntoGrid(initialPoint);
+    const blueNoiseSamples = [initialPoint];
+    const activeList = [initialPoint];
+
+    const findAndInsertPoint = () => {
+        if (activeList.length === 0) return;
+
+        const activePoint = /** @type {vec2} */ getRandomChoice(undefined, activeList);
+        const samplePoints = [...Array(MAX_RETRIES)].map(_ => getSamplePoint(activePoint));
+        const samplePoint = samplePoints.find(isValidPoint);
+
+        if (samplePoint === undefined) {
+            // remove active point from active list
+            const indexOfActivePoint = activeList.indexOf(activePoint);
+            activeList.splice(indexOfActivePoint, 1);
+            return;
+        }
+
+        activeList.push(samplePoint);
+        blueNoiseSamples.push(samplePoint);
+        insertPointIntoGrid(samplePoint);
+    }
+
+    while (activeList.length > 0 && blueNoiseSamples.length < n) {
+        findAndInsertPoint();
+    }
+
+    return blueNoiseSamples.length < n ? [] : blueNoiseSamples;
+}
+
 // === </MATH_UTILS> ===
 
 // === <CREATURE_UTILS> ===
@@ -416,7 +531,6 @@ const createCreature = (
  * Start creature animation
  * @param {Creature} creature
  * @param {(creature: Creature) => Creature} [updateCreature] if undefined, uses identity
- *                                                            (via {@link renderAndUpdateCreature})
  */
 const beginCreatureAnimation = (
   creature,
@@ -441,8 +555,8 @@ const beginCreatureAnimation = (
  */
 const isCreaturesColliding = (creature1, creature2) => {
     return isIntersectingCircles(
-      creature1.positionX, creature1.positionY, CREATURE_WIDTH * 1/2,
-      creature2.positionX, creature2.positionY, CREATURE_WIDTH * 1/2,
+      creature1.positionX, creature1.positionY, CREATURE_WIDTH / 2,
+      creature2.positionX, creature2.positionY, CREATURE_WIDTH / 2,
     )
 }
 
@@ -771,35 +885,34 @@ const resolveCollision = (updatedCreature, allCreatures, creature) => {
 }
 
 window.onload = () => {
-    if (
-      window.matchMedia(`(prefers-reduced-motion: reduce)`).matches
-        || window.matchMedia(`(prefers-reduced-motion: reduce)`).matches
-    ) {
-        // user preference for low motion. do not render creatures
+    // user preference for low motion. do not render creatures
+    if (window.matchMedia(`(prefers-reduced-motion: reduce)`).matches) {
         return;
     }
 
+    const TEST_CREATURE_COUNT = 32;
     const kennelWindowEle = document.querySelector('#kennel-window');
-    const creatures = Array(32).fill('test-creature')
-      .map((name, index) => createCreature(
-        kennelWindowEle,
-        name + index.toString(),
-        undefined, // default sprite sheet
-        getRandomChoice(undefined, [
+
+    const startingPoints = generateBlueNoise(
+        TEST_CREATURE_COUNT, CREATURE_WIDTH,
+        kennelWindowEle.clientLeft, kennelWindowEle.clientTop,
+        kennelWindowEle.clientWidth, kennelWindowEle.clientHeight
+    )
+
+    const creatures = /** @type {Array<Creature>} */ startingPoints
+        .map((startingPoint, index) => createCreature(
+            kennelWindowEle,
+            `test-creature-${index}`,
+            undefined, // use a default sprite sheet
             CreatureState.IDLE,
-            CreatureState.TIRED,
-            CreatureState.SCRATCH_SELF,
-        ]),
-        getRandomInRange(kennelWindowEle.clientLeft, kennelWindowEle.clientLeft + kennelWindowEle.clientWidth),
-        getRandomInRange(kennelWindowEle.clientTop, kennelWindowEle.clientTop + kennelWindowEle.clientHeight),
+            startingPoint.at(0),
+            startingPoint.at(1),
       ))
 
     const updateCreature = updateCreatureWithContext((creature, allCreatures) => {
-        return resolveCollision(
-            CREATURE_STATE_TO_UPDATE_CREATURE_FUNCTION[creature.state](creature, allCreatures),
-            allCreatures,
-            creature,
-        );
+        const updateCreatureFunction = CREATURE_STATE_TO_UPDATE_CREATURE_FUNCTION[creature.state];
+        const updatedCreature = updateCreatureFunction(creature, allCreatures);
+        return resolveCollision(updatedCreature, allCreatures, creature);
     }, creatures);
 
     creatures.forEach((creature) => beginCreatureAnimation(creature, updateCreature))