C# 使用out/ref与返回相比有什么好处?
我正在使用XNA框架制作一个游戏,所以我使用了很多对向量进行操作的函数。(特别是(64位结构)。困扰我的是,大多数方法都是用ref和out参数定义的。以下是一个例子:C# 使用out/ref与返回相比有什么好处?,c#,.net,api,xna,C#,.net,Api,Xna,我正在使用XNA框架制作一个游戏,所以我使用了很多对向量进行操作的函数。(特别是(64位结构)。困扰我的是,大多数方法都是用ref和out参数定义的。以下是一个例子: void Min(ref Vector2 value1, ref Vector2 value2, out Vector2 result) 这对我来说也有点奇怪。还有一个更明显的Min public static Vector2 Min(Vector2 value1, Vector2 value2); 基本上,几乎所有函数都有r
void Min(ref Vector2 value1, ref Vector2 value2, out Vector2 result)
这对我来说也有点奇怪。还有一个更明显的Min
public static Vector2 Min(Vector2 value1, Vector2 value2);
基本上,几乎所有函数都有ref
s和out
s的重载。类似的,其他的
这种设计的好处是什么?XNA针对性能进行了优化,这可能是一种结果吗?比如说,四元数需要128b,其中通过ref较少
编辑:
下面是一个测试代码:
public class Game1 : Microsoft.Xna.Framework.Game
{
GraphicsDeviceManager graphics;
SpriteBatch spriteBatch;
private Vector2 vec1 = new Vector2(1, 2);
private Vector2 vec2 = new Vector2(2, 3);
private Vector2 min;
private string timeRefOut1;
private string timeRefOut2;
private SpriteFont font;
public Game1()
{
graphics = new GraphicsDeviceManager(this);
Content.RootDirectory = "Content";
refOut1();
refOut2();
}
private Vector2 refOut1()
{
Vector2 min = Vector2.Min(vec1, vec2);
return min;
}
private Vector2 refOut2()
{
Vector2.Min(ref vec1, ref vec2, out min);
return min;
}
protected override void Initialize()
{
const int len = 100000000;
Stopwatch stopWatch = new Stopwatch();
stopWatch.Start();
for (int i = 0; i < len; i++)
{
refOut1();
}
stopWatch.Stop();
timeRefOut1 = stopWatch.ElapsedMilliseconds.ToString();
stopWatch.Reset();
stopWatch.Start();
for (int i = 0; i < len; i++)
{
refOut2();
}
stopWatch.Stop();
timeRefOut2 = stopWatch.ElapsedMilliseconds.ToString();
base.Initialize();
}
protected override void LoadContent()
{
spriteBatch = new SpriteBatch(GraphicsDevice);
font = Content.Load<SpriteFont>("SpriteFont1");
}
protected override void Update(GameTime gameTime)
{
if (GamePad.GetState(PlayerIndex.One).Buttons.Back == ButtonState.Pressed)
this.Exit();
base.Update(gameTime);
}
protected override void Draw(GameTime gameTime)
{
GraphicsDevice.Clear(Color.CornflowerBlue);
spriteBatch.Begin();
spriteBatch.DrawString(font, timeRefOut1, new Vector2(200, 200), Color.White);
spriteBatch.DrawString(font, timeRefOut2, new Vector2(200, 300), Color.White);
spriteBatch.End();
// TODO: Add your drawing code here
base.Draw(gameTime);
}
}
及
似乎开销是由温度向量引起的。我还尝试了1GHz WP 7.5设备:
- 1979年
- 1677年
数量级的刻度数迭代次数较少。Vector2是一个结构,这意味着当它作为值返回时,将返回一个副本,而不是返回对现有结构的引用。通过使用ref/out参数,您可以避免此复制,以便在Min方法中创建的向量是
结果
变量中的精确向量
这是一种通常不受欢迎的微优化,但在游戏世界中,这种优化做得足够频繁,在性能非常重要的环境中,值得选择可读性稍差的选项。Servy提到的性能效率之上的另一个不同之处是能够有多个“返回”值:不是以通常的方式返回它们,而是将它们列为ref/var参数。这是我的第一个想法,但它们只返回1个值。@lukas-在本例中,是的,我是为一般情况编写的:)将值类型分配给out/ref参数也是“复制”从局部变量到参数的值。@PeterRitchie整个要点是out/ref参数将在整个方法中用作局部变量,因此您没有从局部变量到out/ref参数的副本。否则,是的,您将执行额外的复制,这将无法达到目的。您仍在将一个变量的值赋给另一个变量(参数)。分配是“复制”操作;只要将值类型赋给变量(无论类型如何),就是在“复制”该值。@PeterRitchie Vector2是一个可变结构。您可以新建一个并将其分配给
result
(结构的一个简单操作),然后根据方法中的逻辑对其进行修改。谢谢!看来这种好处是合理的。10%到50%的速度。我想真正的问题是,“难道.NET不应该做RVO吗?”
.method public hidebysig static void Min(valuetype Microsoft.Xna.Framework.Vector2& value1,
valuetype Microsoft.Xna.Framework.Vector2& value2,
[out] valuetype Microsoft.Xna.Framework.Vector2& result) cil managed
{
// Code size 69 (0x45)
.maxstack 3
IL_0000: ldarg.2
IL_0001: ldarg.0
IL_0002: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0007: ldarg.1
IL_0008: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_000d: blt.s IL_0017
IL_000f: ldarg.1
IL_0010: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0015: br.s IL_001d
IL_0017: ldarg.0
IL_0018: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_001d: stfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0022: ldarg.2
IL_0023: ldarg.0
IL_0024: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0029: ldarg.1
IL_002a: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_002f: blt.s IL_0039
IL_0031: ldarg.1
IL_0032: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0037: br.s IL_003f
IL_0039: ldarg.0
IL_003a: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_003f: stfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0044: ret
} // end of method Vector2::Min
.method public hidebysig static valuetype Microsoft.Xna.Framework.Vector2
Min(valuetype Microsoft.Xna.Framework.Vector2 value1,
valuetype Microsoft.Xna.Framework.Vector2 value2) cil managed
{
// Code size 80 (0x50)
.maxstack 3
.locals init (valuetype Microsoft.Xna.Framework.Vector2 V_0)
IL_0000: ldloca.s V_0
IL_0002: ldarga.s value1
IL_0004: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0009: ldarga.s value2
IL_000b: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0010: blt.s IL_001b
IL_0012: ldarga.s value2
IL_0014: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0019: br.s IL_0022
IL_001b: ldarga.s value1
IL_001d: ldfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0022: stfld float32 Microsoft.Xna.Framework.Vector2::X
IL_0027: ldloca.s V_0
IL_0029: ldarga.s value1
IL_002b: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0030: ldarga.s value2
IL_0032: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0037: blt.s IL_0042
IL_0039: ldarga.s value2
IL_003b: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0040: br.s IL_0049
IL_0042: ldarga.s value1
IL_0044: ldfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_0049: stfld float32 Microsoft.Xna.Framework.Vector2::Y
IL_004e: ldloc.0
IL_004f: ret
} // end of method Vector2::Min