Windows 上，螢幕截圖一般是呼叫 win32 api 完成的，如果 C# 想實現截圖功能，就需要封裝相關 api。在 Windows 上，主要圖形介面有 GDI 和 DirectX。GDI 介面比較靈活，可以擷取指定視窗，哪怕視窗被遮擋或位於顯示區域外，但相容性較低，無法擷取 DX 介面輸出的畫面。DirectX 是高效能圖形介面（當然還有其他功能，與本文無關，忽略不計），主要作為遊戲圖形介面使用，靈活性較低，無法指定擷取特定視窗（或者只是我不會吧），但是相容性較高，可以擷取任何輸出到螢幕的內容，本文提供兩種，根據情況使用。

• GDI+
• Direct3D
• 使用示例

GDI+

以下程式碼使用了 C# 8.0 的新功能，只能使用 VS 2019 編譯，如果需要在老版本 VS 使用，需要自行改造。

public static class CaptureWindow
{
#region 類
/// <summary>
/// Helper class containing User32 API functions
/// </summary>
private class User32
{
[StructLayout(LayoutKind.Sequential)]
public struct RECT
{
public int left;
public int top;
public int right;
public int bottom;
}
[DllImport("user32.dll")]
public static extern IntPtr GetDesktopWindow();
[DllImport("user32.dll")]
public static extern IntPtr GetWindowDC(IntPtr hWnd);
[DllImport("user32.dll")]
public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
[DllImport("user32.dll")]
public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);

[DllImport("user32.dll", EntryPoint = "FindWindow", CharSet = CharSet.Unicode)]
public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
}

private class Gdi32
{

public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter
[DllImport("gdi32.dll")]
public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest,
int nWidth, int nHeight, IntPtr hObjectSource,
int nXSrc, int nYSrc, int dwRop);
[DllImport("gdi32.dll")]
public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth,
int nHeight);
[DllImport("gdi32.dll")]
public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
[DllImport("gdi32.dll")]
public static extern bool DeleteDC(IntPtr hDC);
[DllImport("gdi32.dll")]
public static extern bool DeleteObject(IntPtr hObject);
[DllImport("gdi32.dll")]
public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
}
#endregion

/// <summary>
/// 根據控制代碼截圖
/// </summary>
/// <param name="hWnd">控制代碼</param>
/// <returns></returns>
public static Image ByHwnd(IntPtr hWnd)
{
// get te hDC of the target window
IntPtr hdcSrc = User32.GetWindowDC(hWnd);
// get the size
User32.RECT windowRect = new User32.RECT();
User32.GetWindowRect(hWnd, ref windowRect);
int width = windowRect.right - windowRect.left;
int height = windowRect.bottom - windowRect.top;
// create a device context we can copy to
IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc);
// create a bitmap we can copy it to,
// using GetDeviceCaps to get the width/height
IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height);
// select the bitmap object
IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap);
// bitblt over
Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, Gdi32.SRCCOPY);
// restore selection
Gdi32.SelectObject(hdcDest, hOld);
// clean up
Gdi32.DeleteDC(hdcDest);
User32.ReleaseDC(hWnd, hdcSrc);
// get a .NET image object for it
Image img = Image.FromHbitmap(hBitmap);
// free up the Bitmap object
Gdi32.DeleteObject(hBitmap);
return img;
}

/// <summary>
/// 根據視窗名稱截圖
/// </summary>
/// <param name="windowName">視窗名稱</param>
/// <returns></returns>
public static Image ByName(string windowName)
{
IntPtr handle = User32.FindWindow(null, windowName);
IntPtr hdcSrc = User32.GetWindowDC(handle);
User32.RECT windowRect = new User32.RECT();
User32.GetWindowRect(handle, ref windowRect);
int width = windowRect.right - windowRect.left;
int height = windowRect.bottom - windowRect.top;
IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc);
IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height);
IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap);
Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, Gdi32.SRCCOPY);
Gdi32.SelectObject(hdcDest, hOld);
Gdi32.DeleteDC(hdcDest);
User32.ReleaseDC(handle, hdcSrc);
Image img = Image.FromHbitmap(hBitmap);
Gdi32.DeleteObject(hBitmap);
return img;
}
}
 

Direct3D

安裝 nuget 包 SharpDX.Direct3D11，簡單封裝。此處使用 D3D 11 介面封裝，對多顯示卡多顯示器的情況只能擷取主顯示卡主顯示器畫面，如需擷取其他螢幕，需稍微改造建構函式。截圖可能失敗，也可能擷取到黑屏，已經在返回值中提示。由於不是主要內容，參考即可，程式碼：

public class DirectXScreenCapturer : IDisposable
{
private Factory1 factory;
private Adapter1 adapter;
private SharpDX.Direct3D11.Device device;
private Output output;
private Output1 output1;
private Texture2DDescription textureDesc;
//2D 紋理，儲存截圖資料
private Texture2D screenTexture;

public DirectXScreenCapturer()
{
// 獲取輸出裝置（顯示卡、顯示器），這裡是主顯示卡和主顯示器
factory = new Factory1();
adapter = factory.GetAdapter1(0);
device = new SharpDX.Direct3D11.Device(adapter);
output = adapter.GetOutput(0);
output1 = output.QueryInterface<Output1>();

//設定紋理資訊，供後續使用（截圖大小和質量）
textureDesc = new Texture2DDescription
{
CpuAccessFlags = CpuAccessFlags.Read,
BindFlags = BindFlags.None,
Format = Format.B8G8R8A8_UNorm,
Width = output.Description.DesktopBounds.Right,
Height = output.Description.DesktopBounds.Bottom,
OptionFlags = ResourceOptionFlags.None,
MipLevels = 1,
ArraySize = 1,
SampleDescription = { Count = 1, Quality = 0 },
Usage = ResourceUsage.Staging
};

screenTexture = new Texture2D(device, textureDesc);
}

public Result ProcessFrame(Action<DataBox, Texture2DDescription> processAction, int timeoutInMilliseconds = 5)
{
//截圖，可能失敗
using OutputDuplication duplicatedOutput = output1.DuplicateOutput(device);
var result = duplicatedOutput.TryAcquireNextFrame(timeoutInMilliseconds, out OutputDuplicateFrameInformation duplicateFrameInformation, out SharpDX.DXGI.Resource screenResource);

if (!result.Success) return result;

using Texture2D screenTexture2D = screenResource.QueryInterface<Texture2D>();

//複製資料
device.ImmediateContext.CopyResource(screenTexture2D, screenTexture);
DataBox mapSource = device.ImmediateContext.MapSubresource(screenTexture, 0, MapMode.Read, SharpDX.Direct3D11.MapFlags.None);

processAction?.Invoke(mapSource, textureDesc);

//釋放資源
device.ImmediateContext.UnmapSubresource(screenTexture, 0);
screenResource.Dispose();
duplicatedOutput.ReleaseFrame();

return result;
}

public (Result result, bool isBlackFrame, Image image) GetFrameImage(int timeoutInMilliseconds = 5)
{
//生成 C# 用影象
Bitmap image = new Bitmap(textureDesc.Width, textureDesc.Height, PixelFormat.Format24bppRgb);
bool isBlack = true;
var result = ProcessFrame(ProcessImage);

if (!result.Success) image.Dispose();

return (result, isBlack, result.Success ? image : null);

void ProcessImage(DataBox dataBox, Texture2DDescription texture)
{
BitmapData data = image.LockBits(new Rectangle(0, 0, texture.Width, texture.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);

unsafe
{
byte* dataHead = (byte*)dataBox.DataPointer.ToPointer();

for (int x = 0; x < texture.Width; x++)
{
for (int y = 0; y < texture.Height; y++)
{
byte* pixPtr = (byte*)(data.Scan0 + y * data.Stride + x * 3);

int pos = x + y * texture.Width;
pos *= 4;

byte r = dataHead[pos + 2];
byte g = dataHead[pos + 1];
byte b = dataHead[pos + 0];

if (isBlack && (r != 0 || g != 0 || b != 0)) isBlack = false;

pixPtr[0] = b;
pixPtr[1] = g;
pixPtr[2] = r;
}
}
}

image.UnlockBits(data);
}
}

#region IDisposable Support
private bool disposedValue = false; // 要檢測冗餘呼叫

protected virtual void Dispose(bool disposing)
{
if (!disposedValue)
{
if (disposing)
{
// TODO: 釋放託管狀態(託管物件)。
factory.Dispose();
adapter.Dispose();
device.Dispose();
output.Dispose();
output1.Dispose();
screenTexture.Dispose();
}

// TODO: 釋放未託管的資源(未託管的物件)並在以下內容中替代終結器。
// TODO: 將大型欄位設定為 null。
factory = null;
adapter = null;
device = null;
output = null;
output1 = null;
screenTexture = null;

disposedValue = true;
}
}

// TODO: 僅當以上 Dispose(bool disposing) 擁有用於釋放未託管資源的程式碼時才替代終結器。
// ~DirectXScreenCapturer()
// {
//   // 請勿更改此程式碼。將清理程式碼放入以上 Dispose(bool disposing) 中。
//   Dispose(false);
// }

// 新增此程式碼以正確實現可處置模式。
public void Dispose()
{
// 請勿更改此程式碼。將清理程式碼放入以上 Dispose(bool disposing) 中。
Dispose(true);
// TODO: 如果在以上內容中替代了終結器，則取消註釋以下行。
// GC.SuppressFinalize(this);
}
#endregion
}
 

使用示例

程式碼：

static async Task Main(string[] args)
{
Console.Write("按任意鍵開始DX截圖……");
Console.ReadKey();

string path = @"E:\截圖測試";

var cancel = new CancellationTokenSource();
await Task.Run(() =>
{
Task.Run(() =>
{
Thread.Sleep(5000);
cancel.Cancel();
Console.WriteLine("DX截圖結束！");
});
var savePath = $@"{path}\DX";
Directory.CreateDirectory(savePath);

using var dx = new DirectXScreenCapturer();
Console.WriteLine("開始DX截圖……");

while (!cancel.IsCancellationRequested)
{
var (result, isBlackFrame, image) = dx.GetFrameImage();
if (result.Success && !isBlackFrame) image.Save($@"{savePath}\{DateTime.Now.Ticks}.jpg", ImageFormat.Jpeg);
image?.Dispose();
}
}, cancel.Token);

var windows = WindowEnumerator.FindAll();
for (int i = 0; i < windows.Count; i++)
{
var window = windows[i];
Console.WriteLine($@"{i.ToString().PadLeft(3, ' ')}. {window.Title}
{window.Bounds.X}, {window.Bounds.Y}, {window.Bounds.Width}, {window.Bounds.Height}");
}

var savePath = $@"{path}\Gdi";
Directory.CreateDirectory(savePath);
Console.WriteLine("開始Gdi視窗截圖……");

foreach (var win in windows)
{
var image = CaptureWindow.ByHwnd(win.Hwnd);
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);
image.Dispose();
}
Console.WriteLine("Gdi視窗截圖結束！");

Console.ReadKey();
}