Xna向2D精灵添加重力 [英] Xna adding gravity to a 2d sprite

问题描述

我正在尝试在我的第一个xna 2d游戏中模拟重力.我有以下

        //Used for Jumping
    double elapsedAirTime = 0.0;
    double maxAirTime = 8.35;
    //End Jumping

所以我正在尝试将精灵向上移动一定量，同时经过的AirTime< maxAirTime 但是，存在一个问题，在这段时间内，我的代码似乎只会将精灵向上移动一次，而不是多次向上移动.这是我的"player.cs"类中的代码，或该类的更新方法.

if (newState.IsKeyDown(Keys.Space))
        {
            if(oldState.IsKeyUp(Keys.Space))
            {
                //if we are standing or jumping then change the velocity
                if (playerState == PlayerStates.Standing)
                {
                    playerState = PlayerStates.Jumping;
                    this.position.Y -= (float)(30.0 + ((1.2)*elapsedAirTime)*elapsedAirTime);
                }
            }
        }
        //if we are jumping give it some time
        if (playerState == PlayerStates.Jumping)
        {
            if ((elapsedAirTime < maxAirTime) && position.Y < 3)
            {
                this.position.Y -= (float)(30.0 + ((1.2) * elapsedAirTime)*elapsedAirTime);
                elapsedAirTime += gameTime.ElapsedGameTime.TotalSeconds;
            }
            //otherwise time to fall
            else
            {
                playerState = PlayerStates.Falling;
            }

        }

        //add gravity to falling objects
        if (playerState == PlayerStates.Falling || playerState == PlayerStates.Standing)
        {
            //if we are above the ground
            if (this.position.Y < windowBot - 110)
            {
                //chnage state to falling
                playerState = PlayerStates.Falling;
                this.position.Y += 3.0f + ((float)(gameTime.ElapsedGameTime.TotalSeconds));
            }
            else
            {
                playerState = PlayerStates.Standing;
                elapsedAirTime = 0.0f;
            }
        }

非常感谢您的帮助，谢谢！

解决方案

要使Sprite具有重力感，应在Sprite类中添加速度和加速度.然后，为Sprite创建一个Update方法，并在每次更新中将加速度添加到速度中，并在每次更新中将速度添加到位置中.位置不应该基于飞行时间的长短.您可以将加速度设置为恒定的重力值，然后在每次跳跃时将其添加到Sprite的速度中.这将创建一个看起来不错的流动抛物线跳跃.如果要包括计时，可以将GameTime传递到Sprite的Update方法中，并将其用作速度的修改器.这是一个示例更新方法:

如果使用计时，则此方法有点复杂.您必须跟踪更新花费了多少时间，然后将其除以更新或框架需要花费的平均时间，以获得调整速度所要花费的时间.没有定时，该方法非常简单:

我建议您使用更简单的方法，直到您完全了解计时的工作原理以及为什么需要实现它.

I am trying to simulate gravity in my first xna 2d game. I have the following

        //Used for Jumping
    double elapsedAirTime = 0.0;
    double maxAirTime = 8.35;
    //End Jumping

So I am trying to move the sprite up by a certain amount while the elapsedAirTime < maxAirTime However, there is some issue where my code only seems to move the sprite up once and not multiple times during this segment of time. here is the code in my "player.cs" class, or the update method of the class.

if (newState.IsKeyDown(Keys.Space))
        {
            if(oldState.IsKeyUp(Keys.Space))
            {
                //if we are standing or jumping then change the velocity
                if (playerState == PlayerStates.Standing)
                {
                    playerState = PlayerStates.Jumping;
                    this.position.Y -= (float)(30.0 + ((1.2)*elapsedAirTime)*elapsedAirTime);
                }
            }
        }
        //if we are jumping give it some time
        if (playerState == PlayerStates.Jumping)
        {
            if ((elapsedAirTime < maxAirTime) && position.Y < 3)
            {
                this.position.Y -= (float)(30.0 + ((1.2) * elapsedAirTime)*elapsedAirTime);
                elapsedAirTime += gameTime.ElapsedGameTime.TotalSeconds;
            }
            //otherwise time to fall
            else
            {
                playerState = PlayerStates.Falling;
            }

        }

        //add gravity to falling objects
        if (playerState == PlayerStates.Falling || playerState == PlayerStates.Standing)
        {
            //if we are above the ground
            if (this.position.Y < windowBot - 110)
            {
                //chnage state to falling
                playerState = PlayerStates.Falling;
                this.position.Y += 3.0f + ((float)(gameTime.ElapsedGameTime.TotalSeconds));
            }
            else
            {
                playerState = PlayerStates.Standing;
                elapsedAirTime = 0.0f;
            }
        }

Any help is much appreciated, please and thank you!

解决方案

To give your sprite the feel of gravity, you should add velocity and acceleration to your Sprite class. Then, create an Update method for the Sprite, and have acceleration be added to your velocity every update, and velocity added to position every update. Position should not be based on the amount of elapsed air time. You can set the acceleration to a constant gravitational value, and then add to the velocity of the Sprite whenever you jump. This will create a flowing parabolic jump that looks nice. If you want to include timing, you can pass the GameTime into the Sprite's Update method, and use it as a modifier on the velocity. Here is an example Update method:

void Update(GameTime gt)
{
    int updateTime = gt.ElapsedGameTime.TotalMilliseconds - oldgt.ElapsedGameTime.TotalMilliseconds;
    float timeScalar = updateTime / AVG_FRAME_TIME;
    this.velocity += this.acceleration * timeScalar;
    this.position += this.velocity;
    oldgt = gt;
}

If you use timing, this method is a little complicated. You have to keep track of how much time the update took, then divide it by the average amount of time an update or frame should take to get the amount you should adjust your velocity by. Without timing, the method is very simple:

void Update()
{
    this.velocity += this.acceleration;
    this.position += this.velocity;
}

I would suggest using the simpler method until you understand exactly how timing works and why you need to implement it.

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