浅析如何用C#.NET做屏幕截图软件以及注册全局快捷键(上)
2010-09-30 22:42:43 来源:WEB开发网里面。
现在继续回来说截取透明窗体的问题,我们知道它跟dwRop参数有关,在codeproject上面可以找到的源码,调用BitBlt()时,都是这样的:
BitBlt( hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, PlatformInvokeGDI32.TernaryRasterOperations.SourceCopy);
我想一般的屏幕截图软件也是这样做的,这样做的话,你是不能截取到透明窗体的,我们应该改成这个样子:
BitBlt( hMemDC, 0, 0, size.cx, size.cy, hDC, 0, 0, (uint)(PlatformInvokeGDI32.TernaryRasterOperations.SourceCopy | PlatformInvokeGDI32.TernaryRasterOperations.CaptureBlt) );
通过试验可知是实现了预期效果。CaptureBlt的作用在上面~
需要注意的是,当我们使用BitBlt的时候,涉及设备上下文句柄操作,需要用到另外几个API函数来创建和释放资源。贴个例子:
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;
}
可见虽然直接的平台调用相比Graphics.CopyFromScreen()速度快,灵活,但是还是相当繁琐的。涉及到句柄操作。这些操作在Graphics.CopyFromScreen()已经替我们做了。
下面来说第三种方法:
出处:http://1971ruru.cnblogs.com/
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