爲什麼System.Drawing.Rectangle.getWidth（）如此昂貴？

Question

我正在製作SDL程序，有時需要獲取矩形的寬度。當我做這樣的事情：

 int VideoWidth = Video.Screen.Width; //Expensive operation 
     int VideoHeight = Video.Screen.Height; 

     int ChunksRendered = 0; 
     foreach (Chunk c in Chunks) 
     { 
      if (c.X + 256 + DeferredX > 0 && c.X + DeferredX < VideoWidth) 
      { 
       if (c.Y + 256 + DeferredY > 0 && c.Y + DeferredY < VideoHeight) 
       { 
        BlitSurface.Blit(c.Render(ref Textures, ref BlitSurface), new Point(c.X + DeferredX, c.Y + DeferredY)); 
        ChunksRendered++; 
       } 
      } 
     } 

我得到大約550 FPS我的機器上，但是當我這樣做：

 int ChunksRendered = 0; 
     foreach (Chunk c in Chunks) 
     { 
      if (c.X + 256 + DeferredX > 0 && c.X + DeferredX < Video.Screen.Width) 
      { 
       if (c.Y + 256 + DeferredY > 0 && c.Y + DeferredY < Video.Screen.Height) 
       { 
        BlitSurface.Blit(c.Render(ref Textures, ref BlitSurface), new Point(c.X + DeferredX, c.Y + DeferredY)); 
        ChunksRendered++; 
       } 
      } 
     } 

我只得到大約200 FPS。分析顯然，這會導致速度放慢，但爲什麼要讓這個變量如此昂貴？

Answer 1

很可能是Video.Screen屬性存取器導致這種放緩。如果您正在使用SdlDotNet.dll，這裏是該屬性的代碼：

public static Surface Screen 
{ 
    get 
    { 
     return Surface.FromScreenPtr(Tao.Sdl.Sdl.SDL_GetVideoSurface()); 
    } 
} 

這意味着1個外部DLL函數被調用，1個Surface對象被創建的每個Video.Screen屬性進行訪問的時間。

訪問的SurfaceWidth或Height性質也是昂貴的，因爲它包括調用以下代碼：

internal Tao.Sdl.Sdl.SDL_Surface SurfaceStruct 
{ 
    get 
    { 
     if (this.disposed) 
     { 
      throw new ObjectDisposedException(this.ToString()); 
     } 
     GC.KeepAlive(this); 
     return (Tao.Sdl.Sdl.SDL_Surface) Marshal.PtrToStructure(base.Handle, typeof(Tao.Sdl.Sdl.SDL_Surface)); 
    } 
}