epic/src/epic-collision-intro.ts

0001 /**
0002  * The ePIC collision intro: the electron (blue, from +z) and the ion (red,
0003  * twice the size, from -z) fade in and fly to the interaction point, where
0004  * the event's time animation takes over. Registered by `withEpic()` through
0005  * a dynamic import (three.js).
0006  */
0007
0008 import { Mesh, MeshBasicMaterial, Object3D, SphereGeometry } from 'three';
0009 import type { CollisionIntro } from '@dexvis/firebird-ng';
0010
0011 /** Distance from the interaction point at which the beams start [mm]. */
0012 const START_DISTANCE = 5000;
0013 /** Electron sphere radius [mm]; the ion sphere is twice as large. */
0014 const ELECTRON_RADIUS = 30;
0015 /** Fade-in time of both spheres [ms]. */
0016 const FADE_IN_MS = 300;
0017
0018 export class EpicCollisionIntro implements CollisionIntro {
0019   readonly durationMs = 1000;
0020
0021   private electron: Mesh<SphereGeometry, MeshBasicMaterial> | null = null;
0022   private ion: Mesh<SphereGeometry, MeshBasicMaterial> | null = null;
0023
0024   begin(parent: Object3D): void {
0025     this.electron = this.beamParticle(ELECTRON_RADIUS, 0x0000FF);
0026     this.ion = this.beamParticle(2 * ELECTRON_RADIUS, 0xFF0000);
0027     parent.add(this.electron, this.ion);
0028     this.update(0);
0029   }
0030
0031   update(elapsedMs: number): void {
0032     if (!this.electron || !this.ion) return;
0033     // Linear in time: the spheres meet at the interaction point at durationMs
0034     const opacity = Math.min(1, elapsedMs / FADE_IN_MS);
0035     const distance = START_DISTANCE * (1 - Math.min(1, elapsedMs / this.durationMs));
0036     this.electron.material.opacity = opacity;
0037     this.ion.material.opacity = opacity;
0038     this.electron.position.setZ(distance);
0039     this.ion.position.setZ(-distance);
0040   }
0041
0042   end(): void {
0043     for (const particle of [this.electron, this.ion]) {
0044       if (!particle) continue;
0045       particle.removeFromParent();
0046       particle.geometry.dispose();
0047       particle.material.dispose();
0048     }
0049     this.electron = null;
0050     this.ion = null;
0051   }
0052
0053   private beamParticle(radius: number, color: number): Mesh<SphereGeometry, MeshBasicMaterial> {
0054     return new Mesh(
0055       new SphereGeometry(radius, 32, 32),
0056       new MeshBasicMaterial({ color, transparent: true, opacity: 0 }),
0057     );
0058   }
0059 }