XNA 跳跃简单算法和代码

刚一个朋友问跳跃怎么实现，其实对xna我也不了解，Zzk里搜索“XNA 跳跃”居然没有符合的记录，惊讶之余也有点冲动要不自己也搞一个？不过xna真的是不懂啊，找了两三个源码，笔者实在笨，没能理解它的算法实在见笑了。干脆自己动手从头实现一个，先从现实考虑起跳要考虑的因素是起跳速度（v1）体重(w)重力g然后根据物理xxx记不得了，咱不好高骛远了，simple is perfect 直接上代码：

全局参数：

private bool _isJumping;
private bool _jumpKeyDown;
private float _jumpHeight = 100f;
private TimeSpan _jumpTimeSpan = TimeSpan.FromMilliseconds(500);
private double _jumpStartTime;
private float _jumpStartPosition;

Update中的代码：

_jumpKeyDown = Keyboard.GetState().IsKeyDown(Keys.Space);

squarePosition.Y = DoJump(squarePosition.Y, gameTime);

高度算法函数：

private float DoJump(float velocityY, GameTime gameTime)
{
    if (_jumpKeyDown && !_isJumping)
    {
        _isJumping = true;
        _jumpStartTime = gameTime.TotalGameTime.TotalMilliseconds;
        _jumpStartPosition = velocityY;
    }
    if (_isJumping)
    {
        var jumpTime = gameTime.TotalGameTime.TotalMilliseconds - _jumpStartTime;
        var topTime = _jumpTimeSpan.TotalMilliseconds / 2;
        if (jumpTime < _jumpTimeSpan.TotalMilliseconds)
        {
            if (jumpTime > topTime)
            {
                velocityY =
                    _jumpStartPosition-_jumpHeight - Convert(-(jumpTime - topTime) * _jumpHeight / (_jumpTimeSpan.TotalMilliseconds - topTime));
            }
            else
            {
                velocityY =_jumpStartPosition+ Convert(-( jumpTime)*_jumpHeight/topTime);
            }
        }
        else
        {
            _isJumping = false;
            velocityY = _jumpStartPosition;
        }
 
    }
    return velocityY;
}