Merge pull request #971 from 3DStreet/use-random-seed

Use random seed

src/components/street-generated-clones.js

@@ -1,4 +1,5 @@
 /* global AFRAME */
+import { createRNG } from '../lib/rng';
 
 AFRAME.registerComponent('street-generated-clones', {
   multiple: true,
@@ -10,6 +11,7 @@ AFRAME.registerComponent('street-generated-clones', {
     positionX: { default: 0, type: 'number' },
     positionY: { default: 0, type: 'number' },
     facing: { default: 0, type: 'number' }, // Y Rotation in degrees
+    seed: { default: 0, type: 'int' }, // random seed for random and randomFacing mode
     randomFacing: { default: false, type: 'boolean' },
     direction: { type: 'string', oneOf: ['none', 'inbound', 'outbound'] }, // not used if facing defined?
 
@@ -40,6 +42,18 @@ AFRAME.registerComponent('street-generated-clones', {
   },
 
   update: function (oldData) {
+    // If mode is random or randomFacing and seed is 0, generate a random seed and return,
+    // the update will be called again because of the setAttribute.
+    if (this.data.mode === 'random' || this.data.randomFacing) {
+      if (this.data.seed === 0) {
+        const newSeed = Math.floor(Math.random() * 1000000) + 1; // Add 1 to avoid seed 0
+        this.el.setAttribute(this.attrName, 'seed', newSeed);
+        return;
+      }
+      // Always recreate RNG when update is called to be sure we end of with the same clones positions for a given seed
+      this.rng = createRNG(this.data.seed);
+    }
+
     // Clear existing entities
     this.remove();
 
@@ -115,7 +129,7 @@ AFRAME.registerComponent('street-generated-clones', {
       rotationY = 180 - data.facing;
     }
     if (data.randomFacing) {
-      rotationY = Math.random() * 360;
+      rotationY = this.rng() * 360;
     }
     clone.setAttribute('rotation', `0 ${rotationY} 0`);
 
@@ -131,9 +145,7 @@ AFRAME.registerComponent('street-generated-clones', {
   getModelMixin: function () {
     const data = this.data;
     if (data.modelsArray && data.modelsArray.length > 0) {
-      return data.modelsArray[
-        Math.floor(Math.random() * data.modelsArray.length)
-      ];
+      return data.modelsArray[Math.floor(this.rng() * data.modelsArray.length)];
     }
     return data.model;
   },
@@ -151,8 +163,12 @@ AFRAME.registerComponent('street-generated-clones', {
         // Apply the offset similar to fixed mode
         return start + idx * correctedSpacing;
       });
+    // Use seeded random for shuffling
+    for (let i = positions.length - 1; i > 0; i--) {
+      const j = Math.floor(this.rng() * (i + 1));
+      [positions[i], positions[j]] = [positions[j], positions[i]];
+    }
 
-    // Randomly select positions
-    return positions.sort(() => 0.5 - Math.random()).slice(0, count);
+    return positions.slice(0, count);
   }
 });

src/components/street-generated-pedestrians.js

@@ -1,11 +1,10 @@
 /* global AFRAME */
+import { createRNG } from '../lib/rng';
 
-// a-frame component to generate cloned pedestrian models along a street
 AFRAME.registerComponent('street-generated-pedestrians', {
   multiple: true,
   schema: {
     segmentWidth: {
-      // width of the segment in meters
       type: 'number',
       default: 3
     },
@@ -15,23 +14,20 @@ AFRAME.registerComponent('street-generated-pedestrians', {
       oneOf: ['empty', 'sparse', 'normal', 'dense']
     },
     length: {
-      // length in meters of linear path to fill with clones
       type: 'number'
     },
     direction: {
       type: 'string',
       default: 'none',
       oneOf: ['none', 'inbound', 'outbound']
     },
-    // animated: {
-    //   // load 8 animated characters instead of 16 static characters
-    //   type: 'boolean',
-    //   default: false
-    // },
     positionY: {
-      // y position of pedestrians
       type: 'number',
       default: 0
+    },
+    seed: {
+      type: 'int',
+      default: 0
     }
   },
 
@@ -47,12 +43,22 @@ AFRAME.registerComponent('street-generated-pedestrians', {
 
   remove: function () {
     this.createdEntities.forEach((entity) => entity.remove());
-    this.createdEntities.length = 0; // Clear the array
+    this.createdEntities.length = 0;
   },
 
   update: function (oldData) {
     const data = this.data;
 
+    // Handle seed initialization
+    if (this.data.seed === 0) {
+      const newSeed = Math.floor(Math.random() * 1000000) + 1;
+      this.el.setAttribute(this.attrName, 'seed', newSeed);
+      return;
+    }
+
+    // Create seeded RNG
+    this.rng = createRNG(this.data.seed);
+
     // Clean up old entities
     this.remove();
 
@@ -67,7 +73,7 @@ AFRAME.registerComponent('street-generated-pedestrians', {
       this.densityFactors[data.density] * data.length
     );
 
-    // Get available z positions
+    // Get Z positions using seeded randomization
     const zPositions = this.getZPositions(
       -data.length / 2,
       data.length / 2,
@@ -79,25 +85,23 @@ AFRAME.registerComponent('street-generated-pedestrians', {
       const pedestrian = document.createElement('a-entity');
       this.el.appendChild(pedestrian);
 
-      // Set random position within bounds
+      // Set seeded random position within bounds
       const position = {
         x: this.getRandomArbitrary(xRange.min, xRange.max),
         y: data.positionY,
-        z: zPositions.pop()
+        z: zPositions[i]
       };
       pedestrian.setAttribute('position', position);
 
-      // Set model variant
-      const variantNumber = this.getRandomIntInclusive(
-        1,
-        data.animated ? 8 : 16
-      );
-      const variantPrefix = data.animated ? 'a_char' : 'char';
-      pedestrian.setAttribute('mixin', `${variantPrefix}${variantNumber}`);
+      // Set model variant using seeded random
+      const variantNumber = this.getRandomIntInclusive(1, 16);
+      pedestrian.setAttribute('mixin', `char${variantNumber}`);
 
-      // Set rotation based on direction
-      if (data.direction === 'none' && Math.random() < 0.5) {
-        pedestrian.setAttribute('rotation', '0 180 0');
+      // Set rotation based on direction and seeded random
+      if (data.direction === 'none') {
+        if (this.rng() < 0.5) {
+          pedestrian.setAttribute('rotation', '0 180 0');
+        }
       } else if (data.direction === 'outbound') {
         pedestrian.setAttribute('rotation', '0 180 0');
       }
@@ -111,22 +115,29 @@ AFRAME.registerComponent('street-generated-pedestrians', {
     }
   },
 
-  // Helper methods from legacy function
+  // Helper methods now using seeded RNG
   getRandomIntInclusive: function (min, max) {
     min = Math.ceil(min);
     max = Math.floor(max);
-    return Math.floor(Math.random() * (max - min + 1) + min);
+    return Math.floor(this.rng() * (max - min + 1) + min);
   },
 
   getRandomArbitrary: function (min, max) {
-    return Math.random() * (max - min) + min;
+    return this.rng() * (max - min) + min;
   },
 
   getZPositions: function (start, end, step) {
     const len = Math.floor((end - start) / step) + 1;
-    const arr = Array(len)
+    const positions = Array(len)
       .fill()
       .map((_, idx) => start + idx * step);
-    return arr.sort(() => 0.5 - Math.random());
+
+    // Use seeded shuffle (Fisher-Yates algorithm with seeded RNG)
+    for (let i = positions.length - 1; i > 0; i--) {
+      const j = Math.floor(this.rng() * (i + 1));
+      [positions[i], positions[j]] = [positions[j], positions[i]];
+    }
+
+    return positions;
   }
 });

src/lib/rng.js

@@ -0,0 +1,12 @@
+export function createRNG(seed) {
+  // Create a RNG with the specified seed
+  // Mulberry32 PRNG implementation
+  return (function (a) {
+    return function () {
+      var t = (a += 0x6d2b79f5);
+      t = Math.imul(t ^ (t >>> 15), t | 1);
+      t ^= t + Math.imul(t ^ (t >>> 7), t | 61);
+      return ((t ^ (t >>> 14)) >>> 0) / 4294967296;
+    };
+  })(seed)
+}