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refactor: add softening and reuse Vector3 for gravity calculations #18

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refactor: add softening and reuse Vector3 for gravity calculations #18

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6 changes: 4 additions & 2 deletions src/pages/Simulation/components/PlanetMesh.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ import type React from "react";
import { useEffect, useMemo, useRef } from "react";
import * as THREE from "three";
import type { Planet } from "@/types/planet";
import { calc_gravity_force } from "../utils/gravityUtils";
import { calcGravityForce } from "../utils/gravityUtils";

type PlanetMeshProps = {
planet: Planet;
Expand Down Expand Up @@ -89,6 +89,7 @@ export function PlanetMesh({
}, [planet.id, planetRegistry, planet.mass, planet.radius, ref]);

// 計算用ベクトルをメモリに保持しておく（毎フレームnewしないため）
const force = useMemo(() => new THREE.Vector3(), []);
const forceAccumulator = useMemo(() => new THREE.Vector3(), []);
const myPosVec = useMemo(() => new THREE.Vector3(), []);
const otherPosVec = useMemo(() => new THREE.Vector3(), []);
Expand All @@ -113,13 +114,14 @@ export function PlanetMesh({
const otherMass = otherMesh.userData.mass || 1;
const otherRadius = otherMesh.userData.radius || 0.1;

const force = calc_gravity_force(
calcGravityForce(
myPosVec,
planet.mass,
planet.radius,
otherPosVec,
otherMass,
otherRadius,
force,
);
forceAccumulator.add(force);
}
Expand Down
24 changes: 14 additions & 10 deletions src/pages/Simulation/utils/gravityUtils.ts
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Original file line number Diff line number Diff line change
@@ -1,25 +1,29 @@
import * as THREE from "three";
import type * as THREE from "three";

const G = 1;
const softeningFactor = 0.01;

export function calc_gravity_force(
export function calcGravityForce(
targetPos: THREE.Vector3,
targetMass: number,
targetRadius: number,
sourcePos: THREE.Vector3,
sourceMass: number,
sourceRadius: number,
): THREE.Vector3 {
const direction = new THREE.Vector3().subVectors(sourcePos, targetPos);
const distanceSq = direction.lengthSq();
resultVec: THREE.Vector3,
): void {
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@tknkaa tknkaa Mar 11, 2026

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パフォーマンス上の理由（アロケーションを避ける）であれば納得できるのですが、そうでない場合は Vector3 を返す純粋な関数として定義した方が読みやすいかと思います。関数を純粋に保つことで、後々テストも書きやすくなります。React でもその思想が取り入れられてますね。

const EPS = ((targetRadius + sourceRadius) / 2) * softeningFactor;

resultVec.subVectors(sourcePos, targetPos);
const distanceSq = resultVec.lengthSq() + EPS ** 2;
const distance = Math.sqrt(distanceSq);

// 2つの惑星が接触または重なっている場合は、引力を0にする
const minDistance = targetRadius + sourceRadius;
if (distance < minDistance) {
return new THREE.Vector3(0, 0, 0);
// 距離が0の場合、力は0として扱う（ゼロ除算を避ける）
if (distance === 0) {
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@tknkaa tknkaa Mar 11, 2026

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EPS ** 2 を足しているため、distanceSq が0になることはなく、distance が0になることもないと思うので、このチェックは削除して、EPS の計算箇所に「ゼロ除算を避ける」という意図をコメントで説明するのがいいかと思います。

resultVec.set(0, 0, 0);
return;
}

const forceScalar = (G * targetMass * sourceMass) / (distanceSq * distance);
return direction.multiplyScalar(forceScalar);
resultVec.multiplyScalar(forceScalar);
}