C# wpf 使用GDI实现截屏

wpf截屏系列

第一章使用GDI实现截屏（本章）
第二章使用GDI+实现截屏
 第三章使用DockPanel制作截屏框
 第四章实现截屏框热键截屏
 第五章实现截屏框实时截屏
 第六章使用ffmpeg命令行实现录屏

前言

wpf截屏时通常可以采用gdi+，调用起来比较方便。使用gdi也能实现截屏，截屏数据也能转成BitmapSource对象，当然调用流程会复杂一些，而且需要引入win32方法，唯一比较容易的就是可以直接绘制异或鼠标。

一、导入gdi32

方法一、NuGet获取

这种方法好处是简单方便，缺点是增加了依赖dll，生成的程序容量大一些且附带一些dll。

（1）、获取gdi32

在这里插入图片描述

（2）、获取user32

在这里插入图片描述

方法二、Dllimport

使用DllImport将需要的win32 api导入。这样做工作量比较大，但是好处是无依赖，生成程序很小。
示例如下：

[DllImport(User32, SetLastError = false, ExactSpelling = true)]
public static extern IntPtr GetDC([In, Optional] IntPtr ptr);

完整的gdi需要导入的所有接口见附录。

二、实现步骤

1、创建兼容DC

IntPtr srcHdc = IntPtr.Zero;
IntPtr dstHdc = IntPtr.Zero;
srcHdc = GetDC(hWnd);
dstHdc = CreateCompatibleDC(srcHdc);

2、创建位图

BITMAPINFO bmi = new BITMAPINFO();
IntPtr hBitmap = IntPtr.Zero;
IntPtr oldBitmap = IntPtr.Zero;
bmi.bmiHeader.biSize = (uint)Marshal.SizeOf<BITMAPINFOHEADER>();
bmi.bmiHeader.biWidth = capWidth;
bmi.bmiHeader.biHeight = -capHeight;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 24;
bmi.bmiHeader.biCompression = BitmapCompressionMode.BI_RGB;
bmi.bmiHeader.biSizeImage = 0;
bmi.bmiHeader.biXPelsPerMeter = 0;
bmi.bmiHeader.biYPelsPerMeter = 0;
bmi.bmiHeader.biClrUsed = 0;
bmi.bmiHeader.biClrImportant = 0;
hBitmap = CreateDIBSection(dstHdc, in bmi, DIBColorMode.DIB_RGB_COLORS, out pvBits, IntPtr.Zero, 0);
oldBitmap = SelectObject(dstHdc, hBitmap);

3、获取位图信息

需要获取位图的行对齐stride

BITMAP bitmap;
temp = Marshal.AllocHGlobal(Marshal.SizeOf<BITMAP>());
if (GetObject(hBitmap, Marshal.SizeOf<BITMAP>(), temp) == 0)
{
    throw new Exception("GetObject Failed");
}
bitmap = Marshal.PtrToStructure<BITMAP>(temp);

4、BitBlt

BitBlt(dstHdc, capX, capY, capWidth, capHeight, srcHdc, capX, capY, RasterOperationMode.SRCCOPY | RasterOperationMode.CAPTUREBLT)

5、获取数据

//行对齐
int stride=bitmap.bmWidthBytes;
//宽
int width=bitmap.bmWidth;
//高
int height=bitmap.bmHeight;
//位图数据
IntPtr pBuffer=bitmap.bmBits;

BITMAP转成WriteableBitmap(BitmapSource)

public static WriteableBitmap ToWriteableBitmap(this BITMAP bitmap)
{
    var wb = new WriteableBitmap(bitmap.bmWidth, bitmap.bmHeight, 0, 0, bitmap.bmBitsPixel == 32 ? PixelFormats.Bgra32 : PixelFormats.Bgr24, null);
    wb.WritePixels(new Int32Rect(0, 0, bitmap.bmWidth, bitmap.bmHeight), bitmap.bmBits, bitmap.bmHeight * bitmap.bmWidthBytes, bitmap.bmWidthBytes, 0, 0);
    return wb;
}

6、销毁资源

if (dstHdc != IntPtr.Zero)
{
    if (oldBitmap != IntPtr.Zero)
    {
        var ret = SelectObject(dstHdc, oldBitmap);
        if (ret == IntPtr.Zero)
        {
            errors += "SelectObject Failed";
        }
    }
    if (!DeleteDC(dstHdc))
    {
        errors += "DeleteDC Failed";
    }
}
if (srcHdc != IntPtr.Zero)
{
    if (!ReleaseDC(hWnd, srcHdc))
    {
        errors += "ReleaseDC Failed";
    }
}
if (!DeleteObject(hBitmap))
{
    errors += "DeleteObject Failed";
}
if (temp != IntPtr.Zero) Marshal.FreeHGlobal(temp);

三、封装成对象

/************************************************************************
* @Project:  	GdiGrabber
* @Decription:  gdi图片采集
* 可以根据提供的句柄采集图片或者获取快照。提供了采集区域提供了实际值和比例值
* 两种接口。采集提供了同步和异步两种方式，在主线程或者UI线程建议用异步，在非
* UI线程建议用同步。
* @Verision:  	v1.0.0
* @Author:  	Xin Nie
* @Create:  	2024/03/13 23:57:00
* @LastUpdate:  2024/03/13 23:57:00
************************************************************************
* Copyright @ 2024. All rights reserved.
************************************************************************/
public static class GdiGrabber
{
    /// <summary>
    /// 快照
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <param name="hwnd"></param>
    /// <returns></returns>
    public static WriteableBitmap? Snapshot(int x, int y, int width, int height, nint hWnd = 0, bool isPaintMouse = true);
    /// <summary>
    /// 快照
    /// 按比例，在任意分辨率，比如0,0,1,1就是全屏。
    /// </summary>
    /// <param name="x">比例，0-1</param>
    /// <param name="y">比例，0-1</param>
    /// <param name="width">比例，0-1</param>
    /// <param name="height">比例，0-1</param>
    /// <param name="hwnd"></param>
    /// <returns></returns>
    public static WriteableBitmap? Snapshot(double x, double y, double width, double height, nint hWnd = 0, bool isPaintMouse = true);
    /// <summary>
    /// 采集，异步
    /// 按比例，在任意分辨率，比如0,0,1,1就是全屏。
    /// 用法 await foreach(var i in GdiGrabber.Capture){}
    /// 注意，在UI线程可以直接使用。
    /// 在非UI线程需要确保Dispatcher的运行，比如在线程最后调用Dispatcher.Run()、或 Dispatcher.PushFrame。
    /// </summary>
    /// <param name="x">比例，0-1</param>
    /// <param name="y">比例，0-1</param>
    /// <param name="width">比例，0-1</param>
    /// <param name="height">比例，0-1</param>
    /// <param name="hWnd">句柄，为0则采集桌面</param>
    /// <param name="isPaintMouse">是否绘制鼠标</param>
    /// <returns>采集的数据对象</returns>
    public static IAsyncEnumerable<BITMAP> Capture(double x, double y, double width, double height, nint hWnd = 0, bool isPaintMouse = true);
    /// <summary>
    /// 采集，异步
    /// 用法 await foreach(var i in GdiGrabber.Capture){}
    /// 注意，在UI线程可以直接使用。
    /// 在非UI线程需要确保Dispatcher的运行，比如在线程最后调用Dispatcher.Run()、或 Dispatcher.PushFrame。
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <param name="hWnd">句柄，为0则采集桌面</param>
    /// <param name="isPaintMouse">是否绘制鼠标</param>
    /// <returns>采集的数据对象</returns>
    /// <exception cref="Exception"></exception>
    public static async IAsyncEnumerable<BITMAP> Capture(int x, int y, int width, int height, nint hWnd = 0, bool isPaintMouse = true);
    public static /*IEnumerable<BITMAP>*/void CaptureSync(double x, double y, double width, double height, Func<BITMAP, bool> onGrab, nint hWnd = 0, bool isPaintMouse = true);
    /// <summary>
    /// 采集，同步
    /// </summary>
    /// <param name="x"></param>
    /// <param name="y"></param>
    /// <param name="width"></param>
    /// <param name="height"></param>
    /// <param name="hWnd">句柄，为0则采集桌面</param>
    /// <param name="isPaintMouse">是否绘制鼠标</param>
    /// <param name="onGrab">采集回调，返回是否继续采集。之所以采用回调是因为，更好的设计应该是使用yeild return,但是会出现内存异常读写问题，暂时无法解决。
    /// </param>
    /// <returns>采集的数据对象</returns>
    /// <exception cref="Exception"></exception>
    public static /*IEnumerable<BITMAP>*/void CaptureSync(int x, int y, int width, int height, Func<BITMAP, bool> onGrab, nint hWnd = 0, bool isPaintMouse = false);
    /// <summary>
    /// 将BITMAP转换成WriteableBitmap
    /// 作者的设备测试此操作1080p耗时8ms
    /// </summary>
    /// <param name="bitmap">this</param>
    /// <returns>WriteableBitmap</returns>
    public static WriteableBitmap ToWirteableBitmap(this BITMAP bitmap);
    /// <summary>
    /// 将BITMAP数据拷贝到riteableBitmap
    /// 作者的设备测试此操作1080p耗时2ms
    /// </summary>
    /// <param name="bitmap">this</param>
    /// <param name="wb">WriteableBitmap</param>
    public static void CopyToWriteableBitmap(this BITMAP bitmap, WriteableBitmap wb);
}

四、完整代码

vs2022 .net6.0 wpf项目,采用DllImport的方式无任何依赖。
之后上传

五、使用示例

1、快照

（1）比例值区域截取

截取全屏（任意分辨率）

WriteableBitmap? wb=  GdiGrabber.Snapshot(0,0,1.0,1.0);

（2）实际值区域截取

WriteableBitmap? wb=  GdiGrabber.Snapshot(0,0,600,600);

（3）WPF中使用

WpfGdiGrabber.xaml

<Window x:Class="WpfGdiGrabber.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfGdiGrabber"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid  >
        <Image x:Name="img"></Image>
    </Grid>
</Window>

WpfGdiGrabber.cs

using AC;
using System.Windows;
using System.Windows.Media.Imaging;
namespace WpfGdiGrabber
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            WriteableBitmap? wb = GdiGrabber.Snapshot(0, 0, 1.0, 1.0);
        }
    }
}

效果预览
在这里插入图片描述

2、采集

（1）、异步

UI线程使用

await foreach (var i in GdiGrabber.Capture(0, 0, 1.0, 1.0, 0))
{   
    //img为Image控件
    if (img.Source == null)
        img.Source = i.ToWriteableBitmap();
    else
        i.CopyToWriteableBitmapp(img.Source as WriteableBitmap);
}

非UI线程使用，需要启动一个Dispatcher用于调度消息以及阻塞线程避免结束。

new Thread(async () =>
    {
        bool isExit = false;
        var frame = new DispatcherFrame();
        var func = async () =>
        {
            //循环采集
            await foreach (var i in GdiGrabber.Capture(0, 0, 1.0, 1.0, 0))
            {
                //Dispatcher将操作切换到UI线程执行
                Dispatcher.Invoke(() =>
                {
                    //WriteableBitmap是和线程绑定的，需要在UI线程创建此对象。
                    WriteableBitmap? wb = i.ToWriteableBitmap();
                });
                //退出采集
                if (isExit) break;
            }
            //退出消息循环
            frame.Continue = false;
        };
        func();
        //启动Dispatcher消息循环，此行阻塞
        Dispatcher.PushFrame(frame);
    })
{ IsBackground = true }.Start();

（2）、同步

同步的方式会阻塞，建议在非UI线程中使用。但要注意WriteableBitmap 需要在UI线程中创建才能被控件使用。

GdiGrabber.CaptureSync(0, 0, 1.0, 1.0,  (bitmap) =>
{
    //获取到WriteableBitmap对象
    WriteableBitmap wb = bitmap.ToWriteableBitmap();
    //返回true为继续截屏，false为停止。
    return true;
});

（3）、WPF中使用（异步）

WpfGdiGrabber.xaml

<Window x:Class="WpfGdiGrabber.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfGdiGrabber"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid  >
        <Image x:Name="img"></Image>
    </Grid>
</Window>

WpfGdiGrabber.cs

using AC;
using System.Windows;
using System.Windows.Media.Imaging;
namespace WpfGdiGrabber
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            Capture();
        }
        async void Capture()
        {
            await foreach (var i in GdiGrabber.Capture(0, 0, 1.0, 1.0, 0))
            {
                if (img.Source == null)
                    img.Source = i.ToWriteableBitmap();
                else
                    i.CopyToWriteableBitmap(img.Source as WriteableBitmap);
            }
        }
    }
}

效果预览
在这里插入图片描述

总结

以上就是今天要讲的内容，本文实现了的GDI截屏与GDI+对比性能略差一些，但也是可以一定程度满足使用，比如用来截屏或者制作放大镜。而且有一个好处是可以做到无额外依赖。总的来说，可以作为一种备选方案或者测试方案。

附录

DllImport

    [StructLayout(LayoutKind.Sequential)]
    public struct BITMAP
    {
        public int bmType;
        public int bmWidth;
        public int bmHeight;
        public int bmWidthBytes;
        public ushort bmPlanes;
        public ushort bmBitsPixel;
        public IntPtr bmBits;
    }

    class WinApiImport
    {
        const string Gdi32 = "gdi32.dll";
        const string User32 = "user32.dll";
        [StructLayout(LayoutKind.Sequential), Serializable]
        public struct POINT
        {
            public int X;
            public int Y;
        }
        [StructLayout(LayoutKind.Sequential), Serializable]
        public struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        [StructLayout(LayoutKind.Sequential, Size = 4)]
        public struct RGBQUAD
        {
            public byte rgbBlue;
            public byte rgbGreen;
            public byte rgbRed;
            public byte rgbReserved;
        }
        [StructLayout(LayoutKind.Sequential)]
        public struct BITMAPINFO
        {
            public BITMAPINFOHEADER bmiHeader;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1)]
            public RGBQUAD[] bmiColors;
        }

        public enum BitmapCompressionMode : uint
        {
            BI_RGB = 0,
            BI_RLE8 = 1,
            BI_RLE4 = 2,
            BI_BITFIELDS = 3,
            BI_JPEG = 4,
            BI_PNG = 5
        }

        [StructLayout(LayoutKind.Sequential, Pack = 2)]
        public struct BITMAPINFOHEADER
        {
            public uint biSize;
            public int biWidth;
            public int biHeight;
            public ushort biPlanes;
            public ushort biBitCount;
            public BitmapCompressionMode biCompression;
            public uint biSizeImage;
            public int biXPelsPerMeter;
            public int biYPelsPerMeter;
            public uint biClrUsed;
            public uint biClrImportant;
        }

        public enum DIBColorMode : int
        {
            DIB_RGB_COLORS = 0,
            DIB_PAL_COLORS = 1
        }
        public enum CursorState
        {
            CURSOR_HIDDEN = 0,
            CURSOR_SHOWING = 0x00000001,
            CURSOR_SUPPRESSED = 0x00000002,
        }
        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
        public struct CURSORINFO
        {
            public uint cbSize;
            public CursorState flags;
            public IntPtr hCursor;
            public POINT ptScreenPos;
        }
        [StructLayout(LayoutKind.Sequential)]
        public sealed class ICONINFO
        {
            public bool fIcon;
            public int xHotspot;
            public int yHotspot;
            public IntPtr hbmMask;
            public IntPtr hbmColor;
        }
        public enum RasterOperationMode
        {
            SRCCOPY = 0x00CC0020,
            SRCPAINT = 0x00EE0086,
            SRCAND = 0x008800C6,
            SRCINVERT = 0x00660046,
            SRCERASE = 0x00440328,
            NOTSRCCOPY = 0x00330008,
            NOTSRCERASE = 0x001100A6,
            MERGECOPY = 0x00C000CA,
            MERGEPAINT = 0x00BB0226,
            PATCOPY = 0x00F00021,
            PATPAINT = 0x00FB0A09,
            PATINVERT = 0x005A0049,
            DSTINVERT = 0x00550009,
            BLACKNESS = 0x00000042,
            WHITENESS = 0x00FF0062,
            NOMIRRORBITMAP = -2147483648,
            CAPTUREBLT = 0x40000000
        }
        [DllImport(User32, CharSet = CharSet.Auto, ExactSpelling = true, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        [System.Security.SecurityCritical]
        public static extern bool GetClientRect(IntPtr hWnd, out RECT lpRect);
        [DllImport(User32, SetLastError = false, ExactSpelling = true)]
        public static extern IntPtr GetDesktopWindow();
        [DllImport(User32, SetLastError = false, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool ClientToScreen(IntPtr hWnd, ref POINT lpPoint);
        [DllImport(User32, SetLastError = false, ExactSpelling = true)]
        public static extern IntPtr GetDC([In, Optional] IntPtr ptr);
        [DllImport(Gdi32, ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr CreateCompatibleDC([Optional] IntPtr hDC);
        [DllImport(Gdi32, SetLastError = false, ExactSpelling = true)]
        public static extern IntPtr CreateDIBSection([In, Optional] IntPtr hdc, in BITMAPINFO pbmi, DIBColorMode usage, out IntPtr ppvBits, [In, Optional] IntPtr hSection, [In, Optional] uint offset);
        [DllImport(Gdi32, SetLastError = false, CharSet = CharSet.Auto)]
        public static extern int GetObject(IntPtr hgdiobj, int cbBuffer, IntPtr lpvObject);
        [DllImport(Gdi32, ExactSpelling = true, SetLastError = true)]
        public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
        [DllImport(Gdi32, ExactSpelling = true, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool BitBlt(IntPtr hdc, int nXDest, int nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, RasterOperationMode dwRop);
        [DllImport(Gdi32, ExactSpelling = true, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        [System.Security.SecurityCritical]
        public static extern bool DeleteDC(IntPtr hdc);
        [DllImport(User32, SetLastError = false, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool ReleaseDC(IntPtr hWnd, IntPtr hDC);
        [DllImport(Gdi32, ExactSpelling = true, SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool DeleteObject(IntPtr hObject);
        [DllImport(User32, SetLastError = true, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool GetCursorInfo(ref CURSORINFO pci);
        [DllImport(User32, SetLastError = true, ExactSpelling = true)]
        public static extern IntPtr CopyIcon(IntPtr hIcon);
        [DllImport(User32, SetLastError = true, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool GetIconInfo(IntPtr hIcon, [In, Out] ICONINFO piconinfo);
        [DllImport(User32, SetLastError = true, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool DrawIcon(IntPtr hDC, int X, int Y, IntPtr hIcon);
        [DllImport(User32, SetLastError = true, ExactSpelling = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool DestroyCursor(IntPtr hCursor);
        [DllImport(User32, SetLastError = true, CharSet = CharSet.Auto)]
        public static extern IntPtr LoadCursor(IntPtr hInstance, string lpCursorName);
    }