c# - Deceleration not working as intended

Question

I asked a similar question a few hours ago, but I think there was too much information in that question so I deleted that one and made this one more relevant.

I'm trying to move an object with a decreasing acceleration in a specified time but the acceleration reaches 0 before the object reaches the destination.

I calculate acceleration like this:

//Linear acceleration starts at 0 and finishes at 2.
acceleration = this.elapsed / (this.duration / 2.0f);

Acceleration will be a value between 0 and 2 depending on how much time has elapsed. The value will be closer to 2 when elapsed is closer to (total) duration.

So to calculate a deceleration I would do:

 //Linear deceleration starts at 2 and finishes at 0.
 acceleration = 2.0f - this.elapsed / (this.duration / 2.0f);

This appears to work just fine but the decelerating object never reaches the destination, at around 99% of the distance the elapsedTime becomes greater than total duration, causing the acceleration to become negative. In other words, it appears to have decelerated about 1% too fast.

The original acceleration works perfectly, so does the linear velocity. It's just the deceleration that isn't working properly.

Am I doing something wrong?

Thanks

score 1 · Accepted Answer

在没有看到完整代码的情况下，我认为问题可能是由于在某处float的循环中使用 a 作为迭代变量。for

以下面的程序为例，当我尝试直接使用float作为我的迭代变量时，我能够复制浮点精度在循环中的某处搞砸了。

float duration = 10f;

for(float elapsed = 0.0f; elapsed <= duration; elapsed = elapsed + 0.1f) {
    Console.WriteLine(2.0f - elapsed / (duration / 2.0f));
}

Console.ReadLine();

这个程序的输出是：

您可以看到大约一半的精度射出，这是因为迭代变量本身的精度被搞砸了。

在第二个示例中，我使用 aninteger作为迭代变量，我只是integer在每次迭代中将其缩放到我的计算。这可以防止迭代变量变得混乱：

float duration = 10f;
float offset_scale = 10.0f;

for (int elapsed = 0; elapsed <= (duration * offset_scale); elapsed++) {
    Console.WriteLine(2.0f - (elapsed / offset_scale) / (duration / 2.0f));
}

Console.ReadLine();

该程序的输出是：

2
1.98
1.96
1.94
1.92
1.9
1.88
1.86
1.84
1.82
1.8
1.78
1.76
1.74
1.72
1.7
1.68
1.66
1.64
1.62
1.6
1.58
1.56
1.54
1.52
1.5
1.48
1.46
1.44
1.42
1.4
1.38
1.36
1.34
1.32
1.3
1.28
1.26
1.24
1.22
1.2
1.18
1.16
1.14
1.12
1.1
1.08
1.06
1.04
1.02
1
0.98
0.96
0.94
0.92
0.9
0.88
0.86
0.84
0.82
0.8
0.78
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.42
0.4
0.38
0.36
0.34
0.32
0.3
0.28
0.26
0.24
0.22
0.2
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0

您可以看到精度永远不会变得疯狂，结果正好为 0。

score 1 · Accepted Answer

您可以尝试对浮点数使用 C# Clamp 函数：http: //msdn.microsoft.com/en-us/library/microsoft.xna.framework.mathhelper.clamp.aspx

acceleration = MathHelper.Clamp(2.0f - this.elapsed/(this.duration/2.0f), 0.0, 2.0);

它只是为第一个参数设置一个最小值和最大值。

c# - Deceleration not working as intended

2 回答 2

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