c# - Xna 4 Model Rotation with inertia 在变量更新时无法按预期工作

Question

我正在尝试使用键盘旋转具有惯性阻尼的模型。该代码在固定时间步长下运行良好，但在可变更新频率下表现不同。

更新方法:

protected override void Update(GameTime gameTime)
{
    base.Update(gameTime);

    float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds;
    const float rotationPerSecond = 0.25f;
    const float decayPerSecond = 0.5f;

    KeyboardState kb = Keyboard.GetState();

    if (kb.IsKeyDown(Keys.Left))
    {
        m_velocity += rotationPerSecond * elapsed;
    }
    else if (kb.IsKeyDown(Keys.Right))
    {
        m_velocity -= rotationPerSecond * elapsed;
    }
    else
    {
        if (Math.Abs(m_velocity) < 0.01f)
        {
            m_velocity = 0;
        }
        else if (m_velocity > 0)
        {
            m_velocity -= decayPerSecond * elapsed;
        }
        else if (m_velocity < 0)
        {
            m_velocity += decayPerSecond * elapsed;
        }
    }

    m_rotationAngle += m_velocity;
}  

绘制方法:

Matrix rot = Matrix.CreateWorld(new Vector3(0, 0, 0), Vector3.Forward, Vector3.Up) * 
                         Matrix.CreateRotationY(MathHelper.ToRadians(m_rotationAngle));

我正在改变时间步长

IsFixedTimeStep = true;
graphics.SynchronizeWithVerticalRetrace = true;

和

IsFixedTimeStep = false;
graphics.SynchronizeWithVerticalRetrace = false;

旋转速度和阻尼随着更新频率的不同而完全不同。知道我做错了什么吗？

Answer 1

您在 m_rotationAngle 计算中忘记了 (float)gameTime.ElapsedGameTime.TotalSeconds:

m_rotationAngle += m_velocity * elapsed;

然后增加你的速度值:

const float rotationPerSecond = 250.0f;
const float decayPerSecond = 500.0f;

它适用于:

//IsFixedTimeStep = true/false;
//graphics.SynchronizeWithVerticalRetrace = true/false;