【ゲーム制作】ヒットストップとは？｜TimeScaleで「一瞬の間」を作る演出

// ゲーム全体の「時間の流れる速さ」。1.0が通常速度。
float g_TimeScale = 1.0f;

class HitStop {
public:
    static void Trigger(float duration, float scale = 0.05f) {
        s_Timer = duration;
        s_OriginalScale = g_TimeScale; // 発動前の速度を覚えておく
        g_TimeScale = scale;           // ゲーム全体をスローに
    }

    // 毎フレーム呼ぶ(残り時間管理)。ここは「実時間」で減らすのがポイント。
    static void Update(float realDeltaTime) {
        if (s_Timer <= 0.0f) return;
        s_Timer -= realDeltaTime;
        if (s_Timer <= 0.0f) {
            g_TimeScale = s_OriginalScale; // 元の速度に戻す
        }
    }

    static bool IsActive() { return s_Timer > 0.0f; }

private:
    static float s_Timer;
    static float s_OriginalScale;
};
float HitStop::s_Timer = 0.0f;
float HitStop::s_OriginalScale = 1.0f;

struct Player {
    float x = 0.0f;
    float speed = 6.0f; // 1秒あたり6進む

    void Update(float realDeltaTime) {
        // ゲーム内の移動処理は、必ずTimeScaleを掛けて更新する
        x += speed * g_TimeScale * realDeltaTime;
    }
};

frame  0: TimeScale=1.00  IsActive=0  player.x=0.100
frame  1: TimeScale=1.00  IsActive=0  player.x=0.200
frame  2: TimeScale=1.00  IsActive=0  player.x=0.300
frame  3: TimeScale=1.00  IsActive=0  player.x=0.400
frame  4: TimeScale=1.00  IsActive=0  player.x=0.500
--- frame  5: HitStop::Trigger(0.15f, 0.05f) ---
frame  5: TimeScale=0.05  IsActive=1  player.x=0.505
frame  6: TimeScale=0.05  IsActive=1  player.x=0.510
frame  7: TimeScale=0.05  IsActive=1  player.x=0.515
frame  8: TimeScale=0.05  IsActive=1  player.x=0.520
frame  9: TimeScale=0.05  IsActive=1  player.x=0.525
frame 10: TimeScale=0.05  IsActive=1  player.x=0.530
frame 11: TimeScale=0.05  IsActive=1  player.x=0.535
frame 12: TimeScale=0.05  IsActive=1  player.x=0.540
frame 13: TimeScale=0.05  IsActive=1  player.x=0.545
frame 14: TimeScale=1.00  IsActive=0  player.x=0.550
frame 15: TimeScale=1.00  IsActive=0  player.x=0.650

// 3フレーム目: 1段目の攻撃がヒット
if (frame == 3) {
    HitStop::Trigger(0.3f, 0.05f);
}
// 8フレーム目: まだ1段目のヒットストップ中なのに、2段目がヒット
if (frame == 8) {
    HitStop::Trigger(0.1f, 0.05f);
}

--- frame  3: 1段目ヒット Trigger(0.3f, 0.05f) ---
frame  3: TimeScale=0.050 IsActive=1
--- frame  8: 2段目ヒット Trigger(0.1f, 0.05f) (まだ1段目の最中!) ---
frame  8: TimeScale=0.050 IsActive=1
  ...
frame 13: TimeScale=0.050 IsActive=1
frame 14: TimeScale=0.050 IsActive=0
frame 15: TimeScale=0.050 IsActive=0
frame 16: TimeScale=0.050 IsActive=0
frame 17: TimeScale=0.050 IsActive=0