淺析如何用C#.NET做螢幕截圖軟體以及註冊全域快速鍵（上）

　　最近為了學習C#，決定自己做一個螢幕工具，來代替長久以來每次都要按下PrintScreen鍵然後到Clipboard裡面尋找之麻煩。學以致用~
用C#做螢幕，大致有三種方法。

1、最managed大概就是使用Graphics.CopyFromScreen()方法，此方法有四個重載，不過經反編可見最後調用的都是：

CopyFromScreen(int sourceX, int sourceY, int destinationX, int destinationY, Size blockRegionSize, CopyPixelOperation copyPixelOperation)

 

調用該方法的優點是代碼簡單，不用平台叫用。不過最大的缺點是：不能截取半透明表單。你要想透明表單的話，可以加一個參數，它就是：CopyPixelOperation.CaptureBlt。但是，這樣的話，只能透明表單，截不到螢幕的其他部分了。所以，該方法已經基本可以放棄了。不過我們還是來研究了一下CopyFromScreen()的內部實現吧，看看問題之所在。下面是該方法的具體實現，reflect自System.Drawing.dll

 

CopyFromScreen

public void CopyFromScreen(int sourceX, int sourceY, int destinationX, int destinationY, Size blockRegionSize, CopyPixelOperation copyPixelOperation)
{
switch (copyPixelOperation)
    {
case CopyPixelOperation.NotSourceErase:
case CopyPixelOperation.NotSourceCopy:
case CopyPixelOperation.NoMirrorBitmap:
case CopyPixelOperation.Blackness:
case CopyPixelOperation.SourceErase:
        ...
case CopyPixelOperation.SourceCopy:
case CopyPixelOperation.SourceAnd:
case CopyPixelOperation.MergePaint:
case CopyPixelOperation.SourcePaint:
case CopyPixelOperation.PatCopy:
case CopyPixelOperation.PatPaint:
case CopyPixelOperation.Whiteness:
case CopyPixelOperation.CaptureBlt:
        {
new UIPermission(UIPermissionWindow.AllWindows).Demand();
int width = blockRegionSize.Width;
int height = blockRegionSize.Height;
using (DeviceContext context = DeviceContext.FromHwnd(IntPtr.Zero))
            {
                HandleRef hSrcDC = new HandleRef(null, context.Hdc);
                HandleRef hDC = new HandleRef(null, this.GetHdc());
try
                {
if (SafeNativeMethods.BitBlt(hDC, destinationX, destinationY, width, height, hSrcDC, sourceX, sourceY, (int) copyPixelOperation) == 0)
                    {
throw new Win32Exception();
                    }
                }
finally
                {
this.ReleaseHdc();
                }
            }
return;
        }
    }
throw new InvalidEnumArgumentException("value", (int) copyPixelOperation, typeof(CopyPixelOperation));
}

通過上面代碼可知，類庫裡面最後調用的是windows 的API :BitBlt(),這就是我們要說的第二種方法。

2、平台叫用，即調用windows的API函數。其中要用到的最主要的就是BitBlt()。在此，本人先給各位推薦個網站，它就是：www.pinvoke.net，一個包含幾乎所有API的wiki,裡面一般還含有範例程式碼~為了便於沒有網路的情況下查詢，本人已經把該網站拷貝下來了。。耗費了一天時間做成CHM。。。
先來看看BitBlt()的description:The BitBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context.
這裡，我們只關心它的最後一個參數/// <param name="dwRop">A raster-operation code.</param>
中文翻譯大概叫作：光柵作業碼。大概就是控制從source device context 到 destination device context的拷貝方式。它是一個DWORD類型，取值在

// Summary:    //     Determines how the source color in a copy pixel operation is combined with    //     the destination color to result in a final color.    public enum CopyPixelOperation    {        // Summary:        //     The bitmap is not mirrored.        NoMirrorBitmap = -2147483648,        //        // Summary:        //     The destination area is filled by using the color associated with index 0        //     in the physical palette. (This color is black for the default physical palette.)        Blackness = 66,        //        // Summary:        //     The source and destination colors are combined using the Boolean OR operator,        //     and then resultant color is then inverted.        NotSourceErase = 1114278,        //        // Summary:        //     The inverted source area is copied to the destination.        NotSourceCopy = 3342344,        //        // Summary:        //     The inverted colors of the destination area are combined with the colors        //     of the source area using the Boolean AND operator.        SourceErase = 4457256,        //        // Summary:        //     The destination area is inverted.        DestinationInvert = 5570569,        //        // Summary:        //     The colors of the brush currently selected in the destination device context        //     are combined with the colors of the destination are using the Boolean XOR        //     operator.        PatInvert = 5898313,        //        // Summary:        //     The colors of the source and destination areas are combined using the Boolean        //     XOR operator.        SourceInvert = 6684742,        //        // Summary:        //     The colors of the source and destination areas are combined using the Boolean        //     AND operator.        SourceAnd = 8913094,        //        // Summary:        //     The colors of the inverted source area are merged with the colors of the        //     destination area by using the Boolean OR operator.        MergePaint = 12255782,        //        // Summary:        //     The colors of the source area are merged with the colors of the selected        //     brush of the destination device context using the Boolean AND operator.        MergeCopy = 12583114,        //        // Summary:        //     The source area is copied directly to the destination area.        SourceCopy = 13369376,        //        // Summary:        //     The colors of the source and destination areas are combined using the Boolean        //     OR operator.        SourcePaint = 15597702,        //        // Summary:        //     The brush currently selected in the destination device context is copied        //     to the destination bitmap.        PatCopy = 15728673,        //        // Summary:        //     The colors of the brush currently selected in the destination device context        //     are combined with the colors of the inverted source area using the Boolean        //     OR operator. The result of this operation is combined with the colors of        //     the destination area using the Boolean OR operator.        PatPaint = 16452105,        //        // Summary:        //     The destination area is filled by using the color associated with index 1        //     in the physical palette. (This color is white for the default physical palette.)        Whiteness = 16711778,        //        // Summary:        //     Windows that are layered on top of your window are included in the resulting        //     image. By default, the image contains only your window. Note that this generally        //     cannot be used for printing device contexts.        CaptureBlt = 1073741824,    }

裡面。

現在繼續回來說截取透明表單的問題，我們知道它跟dwRop參數有關，在codeproject上面可以找到的源碼，調用BitBlt()時，都是這樣的：

BitBlt( hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, PlatformInvokeGDI32.TernaryRasterOperations.SourceCopy);

我想一般的螢幕軟體也是這樣做的，這樣做的話，你是不能截取到透明表單的，我們應該改成這個樣子：

BitBlt( hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, (uint)(PlatformInvokeGDI32.TernaryRasterOperations.SourceCopy | PlatformInvokeGDI32.TernaryRasterOperations.CaptureBlt) );

通過實驗可知是實現了預期效果。CaptureBlt的作用在上面~
需要注意的是，當我們使用BitBlt的時候，涉及裝置上下文控制代碼操作，需要用到另外幾個API函數來建立和釋放資源。貼個例子：

 

GetDesktopImage

public static Bitmap GetDesktopImage()
        {
//In size variable we shall keep the size of the screen.
            SIZE size;

//Variable to keep the handle to bitmap.
            IntPtr hBitmap;

//Here we get the handle to the desktop device context.
            IntPtr     hDC = PlatformInvokeUSER32.GetDC(PlatformInvokeUSER32.GetDesktopWindow()); 

//Here we make a compatible device context in memory for screen device context.
            IntPtr hMemDC = PlatformInvokeGDI32.CreateCompatibleDC(hDC);

//We pass SM_CXSCREEN constant to GetSystemMetrics to get the X coordinates of screen.
            size.cx = PlatformInvokeUSER32.GetSystemMetrics(PlatformInvokeUSER32.SM_CXSCREEN);

//We pass SM_CYSCREEN constant to GetSystemMetrics to get the Y coordinates of screen.
            size.cy = PlatformInvokeUSER32.GetSystemMetrics(PlatformInvokeUSER32.SM_CYSCREEN);

//We create a compatible bitmap of screen size using screen device context.
            hBitmap = PlatformInvokeGDI32.CreateCompatibleBitmap(hDC, size.cx, size.cy);

//As hBitmap is IntPtr we can not check it against null. For this purspose IntPtr.Zero is used.
            if (hBitmap!=IntPtr.Zero)
            {
//Here we select the compatible bitmap in memeory device context and keeps the refrence to Old bitmap.
                IntPtr hOld = (IntPtr) PlatformInvokeGDI32.SelectObject(hMemDC, hBitmap);
//We copy the Bitmap to the memory device context.
                PlatformInvokeGDI32.BitBlt( hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, (uint)(PlatformInvokeGDI32.TernaryRasterOperations.SRCCOPY | PlatformInvokeGDI32.TernaryRasterOperations.CAPTUREBLT) );
//We select the old bitmap back to the memory device context.
                PlatformInvokeGDI32.SelectObject(hMemDC, hOld);
//We delete the memory device context.
                PlatformInvokeGDI32.DeleteDC(hMemDC);
//We release the screen device context.
                PlatformInvokeUSER32.ReleaseDC(PlatformInvokeUSER32.GetDesktopWindow(), hDC);
//Image is created by Image bitmap handle and stored in local variable.
                Bitmap bmp = System.Drawing.Image.FromHbitmap(hBitmap); 
//Release the memory to avoid memory leaks.
                PlatformInvokeGDI32.DeleteObject(hBitmap);
//This statement runs the garbage collector manually.
                GC.Collect();
//Return the bitmap 
                return bmp;
            }

//If hBitmap is null retunrn null.
            return null;
        }

 

 

可見雖然直接的平台叫用相比Graphics.CopyFromScreen()速度快，靈活，但是還是相當繁瑣的。涉及到控制代碼操作。這些操作在Graphics.CopyFromScreen()已經替我們做了。
下面來說第三種方法：

待續~淺析如何用C#.NET做螢幕軟體以及註冊全域快速鍵（下）