Bitmap.SetPixel在f#中的作用比在c#中慢 [英] Bitmap.SetPixel acts slower in f# than in c#
问题描述
f#代码实际上比c#代码慢500倍.我究竟做错了什么? 我试图使两种语言的代码基本相同. SetPixel在f#中的运行速度这么慢没有意义.
The f# code goes literally 500 times slower than the c# code. What am I doing wrong? I tried to make the code basically the same for both languages. It doesn't make sense that SetPixel would be that much slower in f#.
F#:
module Imaging
open System.Drawing;
#light
type Image (width : int, height : int) = class
member z.Pixels = Array2D.create width height Color.White
member z.Width with get() = z.Pixels.GetLength 0
member z.Height with get() = z.Pixels.GetLength 1
member z.Save (filename:string) =
let bitmap = new Bitmap(z.Width, z.Height)
let xmax = bitmap.Width-1
let ymax = bitmap.Height-1
let mutable bob = 0;
for x in 0..xmax do
for y in 0..ymax do
bitmap.SetPixel(x,y,z.Pixels.[x,y])
bitmap.Save(filename)
new() = Image(1280, 720)
end
let bob = new Image(500,500)
bob.Save @"C:\Users\White\Desktop\TestImage2.bmp"
C#:
using System.Drawing;
namespace TestProject
{
public class Image
{
public Color[,] Pixels;
public int Width
{
get
{
return Pixels.GetLength(0);
}
}
public int Height
{
get
{
return Pixels.GetLength(1);
}
}
public Image(int width, int height)
{
Pixels = new Color[width, height];
for (int x = 0; x < Width; x++)
{
for (int y = 0; y < Height; y++)
{
Pixels[x, y] = Color.White;
}
}
}
public void Save(string filename)
{
Bitmap bitmap = new Bitmap(Width, Height);
for (int x = 0; x < bitmap.Width; x++)
{
for (int y = 0; y < bitmap.Height; y++)
{
bitmap.SetPixel(x, y, Pixels[x, y]);
}
}
bitmap.Save(filename);
}
}
class Program
{
static void Main(string[] args)
{
Image i = new Image(500, 500);
i.Save(@"C:\Users\White\Desktop\TestImage2.bmp");
}
}
}
推荐答案
您在F#中对Pixels
属性的定义是错误的:每次访问其值时(例如在Save
的内部循环中),该定义将重新评估.您应该改用以下形式:
Your definition of the Pixels
property in F# is wrong: each time its value is accessed (e.g. in the inner loop of Save
), the definition will be reevaluated. You should use this form instead:
member val Pixels = Array2D.create width height Color.White
这将在调用构造函数时对右侧进行一次评估,然后缓存该值.
This will evaluate the right-hand side exactly once, when the constructor is called, and then cache the value.
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