Windows 上，屏幕截图一般是调用 win32 api 完成的，如果 C# 想实现截图功能，就需要封装相关 api。在 Windows 上，主要图形接口有 GDI 和 DirectX。GDI 接口比较灵活，可以截取指定窗口，哪怕窗口被遮挡或位于显示区域外，但兼容性较低，无法截取 DX 接口输出的画面。DirectX 是高性能图形接口（当然还有其他功能，与本文无关，忽略不计），主要作为游戏图形接口使用，灵活性较低，无法指定截取特定窗口（或者只是我不会吧），但是兼容性较高，可以截取任何输出到屏幕的内容，根据情况使用。
正文以下代码使用了 C# 8.0 的新功能，只能使用 VS 2019 编译，如果需要在老版本 VS 使用，需要自行改造。
GDI用静态类简单封装 GDI 接口并调用接口截图。
1 public static class CaptureWindow 2 { 3 #region 类 4 /// <summary> 5 /// Helper class containing User32 API functions 6 /// </summary> 7 private class User32 8 { 9 [StructLayout(LayoutKind.Sequential)] 10 public struct RECT 11 { 12 public int left; 13 public int top; 14 public int right; 15 public int bottom; 16 } 17 [DllImport("user32.dll")] 18 public static extern IntPtr GetDesktopWindow(); 19 [DllImport("user32.dll")] 20 public static extern IntPtr GetWindowDC(IntPtr hWnd); 21 [DllImport("user32.dll")] 22 public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC); 23 电脑 [DllImport("user32.dll")] 24 public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect); 25 26 [DllImport("user32.dll", EntryPoint = "FindWindow", CharSet = CharSet.Unicode)] 27 public static extern IntPtr FindWindow(string lpClassName, string lpWindowName); 28 } 29 30 private class Gdi32 31 { 32 33 public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter 34 [DllImport("gdi32.dll")] 35 public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest, 36 int nWidth, int nHeight, IntPtr hObjectSource, 37 int nXSrc, int nYSrc, int dwRop); 38 [DllImport("gdi32.dll")] 39 public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth, 40 int 电脑 nHeight); 41 [DllImport("gdi32.dll")] 42 public static extern IntPtr CreateCompatibleDC(IntPtr hDC); 43 [DllImport("gdi32.dll")] 44 public static extern bool DeleteDC(IntPtr hDC); 45 [DllImport("gdi32.dll")] 46 public static extern bool DeleteObject(IntPtr hObject); 47 [DllImport("gdi32.dll")] 48 public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject); 49 } 50 #endregion 51 52 /// <summary> 53 /// 根据句柄截图 54 /// </summary> 55 /// <param name="hWnd">句柄</param> 56 /// <returns></returns> 57 public static Image ByHwnd(IntPtr hWnd) 58 { 59 // get te hDC of the target window 60 IntPtr hdcSrc = User32.GetWindowDC(hWnd); 电脑 61 // get the size 62 User32.RECT windowRect = new User32.RECT(); 63 User32.GetWindowRect(hWnd, ref windowRect); 64 int width = windowRect.right - windowRect.left; 65 int height = windowRect.bottom - windowRect.top; 66 // create a device context we can copy to 67 IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc); 68 // create a bitmap we can copy it to, 69 // using GetDeviceCaps to get the width/height 70 IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height); 71 // select the bitmap object 72 IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap); 73 // bitblt over 74 Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, Gdi32.SRCCOPY); 75 // restore selection 76 Gdi32.SelectObject(hdcDest, hOld); 77 // clean up 78 Gdi32.DeleteDC(hdcDest); 79 User32.ReleaseDC(hWnd, hdcSrc); 80 // get a .NET image object for it 81 Image img = Image.FromHbitmap(hBitmap); 82 // free up the Bitmap object 83 Gdi32.DeleteObject(hBitmap); 84 return img; 85 } 86 87 /// <summary> 88 /// 根据窗口名称截图 89 /// </summary> 90 /// <param name="windowName">窗口名称</param> 91 /// <returns></returns> 92 public static Image ByName(string windowName) 93 { 94 IntPtr handle = User32.FindWindow(null, windowName); 95 IntPtr hdcSrc = User32.GetWindowDC(handle); 96 User32.RECT windowRect = new User32.RECT(); 97 User32.GetWindowRect(handle, ref windowRect); 98 int width = windowRect.right - windowRect.left; 99 int height = windowRect.bottom - windowRect.top;100 IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc);101 IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height);102 IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap);103 Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, Gdi32.SRCCOPY);104 Gdi32.SelectObject(hdcDest, hOld);105 Gdi32.DeleteDC(hdcDest);106 User32.ReleaseDC(handle, hdcSrc);107 Image img = Image.FromHbitmap(hBitmap);108 Gdi32.DeleteObject(hBitmap);109 return img;110 }111 }Direct3D
安装 nuget 包 SharpDX.Direct3D11，简单封装。此处使用 D3D 11 接口封装，对多显卡多显示器的情况只能截取主显卡主显示器画面，如需截取其他屏幕，需稍微改造构造函数。截屏可能失败，也可能截取到黑屏，已经在返回值中提示。
将 DX 截屏转换成 C# 图像使用了指针操作，一方面可以提升性能，一方面也是因为都用 DX 了，基本上是很难避免底层操作了，那就一不做二不休，多利用一下。
1 public class DirectXScreenCapturer : IDisposable 2 { 3 private Factory1 factory; 4 private Adapter1 adapter; 5 private SharpDX.Direct3D11.Device device; 6 private Output output; 7 private Output1 output1; 8 private Texture2DDescription textureDesc; 9 //2D 纹理，存储截屏数据 10 private Texture2D screenTexture; 11 12 public DirectXScreenCapturer() 13 { 14 // 获取输出设备（显卡、显示器），这里是主显卡和主显示器 15 factory = new Factory1(); 16 adapter = factory.GetAdapter1(0); 17 device = new SharpDX.Direct3D11.Device(adapter); 18 output = adapter.GetOutput(0); 19 output1 = output.QueryInterface<Output1>(); 20 21 //设置纹理信息，供后续使用（截图大小和质量） 22 textureDesc = new Texture2DDescription 23 { 24 CpuAccessFlags = CpuAccessFlags.Read, 25 BindFlags = BindFlags.None, 26 Format = Format.B8G8R8A8_UNorm, 27 Width = output.Description.DesktopBounds.Right, 28 Height = output.Description.DesktopBounds.Bottom, 29 OptionFlags = ResourceOptionFlags.None, 30 MipLevels = 1, 31 ArraySize = 1, 32 SampleDescription = { Count = 1, Quality = 0 }, 33 Usage = ResourceUsage.Staging 34 }; 35 36 screenTexture = new Texture2D(device, textureDesc); 37 } 38 39 public Result ProcessFrame(Action<DataBox, Texture2DDescription> processAction, int timeoutInMilliseconds = 5) 40 { 41 //截屏，可能失败 42 using OutputDuplication duplicatedOutput = output1.DuplicateOutput(device); 43 var result = duplicatedOutput.TryAcquireNextFrame(timeoutInMilliseconds, out OutputDuplicateFrameInformation duplicateFrameInformation, out SharpDX.DXGI.Resource screenResource); 44 45 if (!result.Success) return result; 46 47 using Texture2D screenTexture2D = screenResource.QueryInterface<Texture2D>(); 48 49 //复制数据 50 device.ImmediateContext.CopyResource(screenTexture2D, screenTexture); 51 DataBox mapSource = device.ImmediateContext.MapSubresource(screenTexture, 0, MapMode.Read, SharpDX.Direct3D11.MapFlags.None); 52 53 processAction?.Invoke(mapSource, textureDesc); 54 55 //释放资源 56 device.ImmediateContext.UnmapSubresource(screenTexture, 0); 57 screenResource.Dispose(); 58 duplicatedOutput.ReleaseFrame(); 59 60 return result; 61 } 62 63 public (Result result, bool isBlackFrame, Image image) GetFrameImage(int timeoutInMilliseconds = 5) 64 { 65 //生成 C# 用图像 66 Bitmap image = new Bitmap(textureDesc.Width, textureDesc.Height, PixelFormat.Format24bppRgb); 67 bool isBlack = true; 68 var result = ProcessFrame(ProcessImage); 69 70 if (!result.Success) image.Dispose(); 71 72 return (result, isBlack, result.Success ? image : null); 73 74 void ProcessImage(DataBox dataBox, Texture2DDescription texture) 75 { 76 BitmapData data = image.LockBits(new Rectangle(0, 0, texture.Width, texture.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); 77 78 unsafe 79 { 80 byte* dataHead = (byte*)dataBox.DataPointer.ToPointer(); 81 82 for (int x = 0; x < texture.Width; x++) 83 { 84 for (int y = 0; y < texture.Height; y++) 85 { 86 byte* pixPtr = (byte*)(data.Scan0 + y * data.Stride + x * 3); 87 88 int pos = x + y * texture.Width; 89 pos *= 4; 90 91 byte r = dataHead[pos + 2]; 92 byte g = dataHead[pos + 1]; 93 byte b = dataHead[pos + 0]; 94 95 if (isBlack && (r != 0 || g != 0 || b != 0)) isBlack = false; 96 97 pixPtr[0] = b; 98 pixPtr[1] = g; 99 pixPtr[2] = r;100 }101 }102 }103 104 image.UnlockBits(data);105 }106 }107 108 #region IDisposable Support109 private bool disposedValue = false; // 要检测冗余调用110 111 protected virtual void Dispose(bool disposing)112 {113 if (!disposedValue)114 {115 if (disposing)116 {117 // TODO: 释放托管状态(托管对象)。118 factory.Dispose();119 adapter.Dispose();120 device.Dispose();121 output.Dispose();122 output1.Dispose();123 screenTexture.Dispose();124 }125 126 // TODO: 释放未托管的资源(未托管的对象)并在以下内容中替代终结器。127 // TODO: 将大型字段设置为 null。128 factory = null;129 adapter = null;130 device = null;131 output = null;132 output1 = null;133 screenTexture = null;134 135 disposedValue = true;136 }137 }138 139 // TODO: 仅当以上 Dispose(bool disposing) 拥有用于释放未托管资源的代码时才替代终结器。140 // ~DirectXScreenCapturer()141 // {142 // // 请勿更改此代码。将清理代码放入以上 Dispose(bool disposing) 中。143 // Dispose(false);144 // }145 146 // 添加此代码以正确实现可处置模式。147 public void Dispose()148 {149 // 请勿更改此代码。将清理代码放入以上 Dispose(bool disposing) 中。150 Dispose(true);151 // TODO: 如果在以上内容中替代了终结器，则取消注释以下行。152 // GC.SuppressFinalize(this);153 }154 #endregion155 }使用示例
其中使用了窗口枚举辅助类，详细代码请看文章末尾的 Github 项目。支持 .Net Core。
1 static async Task Main(string[] args) 2 { 3 Console.Write("按任意键开始DX截图……"); 4 Console.ReadKey(); 5 6 string path = @"E:\截图测试"; 7 8 var cancel = new CancellationTokenSource(); 9 await Task.Run(() =>10 {11 Task.Run(() =>12 {13 Thread.Sleep(5000);14 cancel.Cancel();15 Console.WriteLine("DX截图结束！");16 });17 var savePath = $@"{path}\DX";18 Directory.CreateDirectory(savePath);19 20 using var dx = new DirectXScreenCapturer();21 Console.WriteLine("开始DX截图……");22 23 while (!cancel.IsCancellationRequested)24 {25 var (result, isBlackFrame, image) = dx.GetFrameImage();26 if (result.Success && !isBlackFrame) image.Save($@"{savePath}\{DateTime.Now.Ticks}.jpg", ImageFormat.Jpeg);27 image?.Dispose();28 }29 }, cancel.Token);30 31 var windows = WindowEnumerator.FindAll();32 for (int i = 0; i < windows.Count; i++)33 {34 var window = windows[i];35 Console.WriteLine($@"{i.ToString().PadLeft(3, ' ')}. {window.Title}36 {window.Bounds.X}, {window.Bounds.Y}, {window.Bounds.Width}, {window.Bounds.Height}");37 }38 39 var savePath = $@"{path}\Gdi";40 Directory.CreateDirectory(savePath);41 Console.WriteLine("开始Gdi窗口截图……");42 43 foreach (var win in windows)44 {45 var image = CaptureWindow.ByHwnd(win.Hwnd);46 image.Save($@"{savePath}\{win.Title.Substring(win.Title.LastIndexOf(@"\") < 0 ? 0 : win.Title.LastIndexOf(@"\") + 1).Replace("/", "").Replace("*", "").Replace("?", "").Replace("\"", "").Replace(":", "").Replace("<", "").Replace(">", "").Replace("|", "")}.jpg", ImageFormat.Jpeg);47 image.Dispose();48 }49 Console.WriteLine("Gdi窗口截图结束！");50 51 Console.ReadKey();52 }结语
这个示例代码中的 DX 截图只支持 win7 以上版本，xp 是时候退出历史舞台了。代码参考了网上大神的文章，并根据实际情况进行改造，尽可能简化实现和使用代码，展示最简单情况下所必须的代码。如果实际需求比较复杂，可以以这个为底版进行改造。
电脑
