C# wpf 使用GDI+实现截屏

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前言

wpf做屏幕录制或者屏幕广播之类的功能时需要实现截屏，在C#中比较容易实现的截屏方法是使用GDI+，本文将展示使用GDI+截屏的具体实现方案，包括如何绘制鼠标，按帧率采集屏幕、将GDI+对象转成wpf对象等。

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一、引用System.Drawing

在wpf中使用GDI+功能需要引入System.Drawing库，有2种方式：在.net framework中直接引用系统库即可。在.net core中可以引用mono实现的跨平台的System.Drawing，提供接口与系统程序集是一模一样的，而且性能略好一些。

方法一、引用系统程序集

1、右键引用

2、搜索drawing，勾选后确定即可。

方法二、NuGet获取跨平台Drawing

在.net core中无法引用系统的Drawing，只能通过Nuget获取跨平台Drawing。
1、右键引用打开NuGet界面

2、搜索drawing并安装

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二、实现截屏

1.简单截屏

简单的截屏只需几行代码即可实现：

/// <summary>
/// 截取一帧图片
/// </summary>
/// <param name="x">x坐标</param>
/// <param name="y">y坐标</param>
/// <param name="width">宽</param>
/// <param name="height">高</param>
/// <returns>截屏后的位图对象，需要调用Dispose手动释放资源。</returns>
public static System.Drawing.Bitmap Snapshot(int x, int y, int width, int height)
{
    
    
    System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
    using (System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(bitmap))
    {
    
    
         graphics.CopyFromScreen(x, y, 0, 0, new System.Drawing.Size(width, height), System.Drawing.CopyPixelOperation.SourceCopy);
    }
    return bitmap;
}

2.绘制鼠标

上述方式实现的截屏是没有鼠标的，如果要显示鼠标则需要我们手动绘制，通过获取鼠标的icon绘制到背景图像中。绘制鼠标需要用到win32Api以及gdi的rop。大致步骤如下（示例）：

CURSORINFO ci;
ICONINFO info = new ICONINFO();
ci.cbSize = Marshal.SizeOf(typeof(CURSORINFO));
if (GetCursorInfo(out ci))
{
    
    
    if (GetIconInfo(ci.hCursor, info))
    {
    
    
        if (异或光标)
        {
    
    
            使用gdi的rop绘制
        }
        else
        {
    
    
            using (var icon = System.Drawing.Icon.FromHandle(ci.hCursor))
            {
    
    
                graphics.DrawIcon(icon, mouseX, mouseY);
            }
        }
    }
}

3.转换成wpf对象

参考我的另一篇文章《C# wpf Bitmap转换成WriteableBitmap（BitmapSource）的方法》

4.屏幕采集

基于上面的实现加上开线程及循环截屏就可以做到屏幕采集了。示例代码如下：

System.Drawing.Bitmap bitmap = new System.Drawing.Bitmap(width, height, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
using (System.Drawing.Graphics graphics = System.Drawing.Graphics.FromImage(bitmap))
{
    
    
    while (!_exitFlag)
    {
    
    
        graphics.CopyFromScreen(x, y, 0, 0, new System.Drawing.Size(width, height), System.Drawing.CopyPixelOperation.SourceCopy);
        //绘制鼠标
        ...
       //绘制鼠标--end
       //将位图数据写入wpf对象、编码推流等
         ...
       //将位图数据写入wpf对象、编码推流等--end
       Thread.Sleep(帧率延时);
    }
}

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三、完整代码

通过上述方法得到的接口设计如下（不含具体实现）：

/// <summary>
/// 截屏事件参数
/// </summary>
public class ScreenCaptureEventArgs : EventArgs
{
    
    
    /// <summary>
    /// 像素格式
    /// </summary>
    public System.Drawing.Imaging.PixelFormat PixelFormat {
    
     set; get; }
    /// <summary>
    /// 图像宽
    /// </summary>
    public int Width {
    
     set; get; }
    /// <summary>
    /// 图像高
    /// </summary>
    public int Height {
    
     set; get; }
}
/// <summary>
/// 截屏数据事件参数
/// </summary>
public class ScreenCaptureDataEventArgs : ScreenCaptureEventArgs
{
    
    
    /// <summary>
    /// 图像数据
    /// </summary>
    public IntPtr Data {
    
     set; get; }
    /// <summary>
    /// 数据长度
    /// </summary>
    public int Length {
    
     set; get; }
    /// <summary>
    /// 一行数据长度
    /// </summary>
    public int Stride {
    
     set; get; }
}
/// <summary>
/// 数值类型
/// </summary>
public enum ScreenCaptureValueType
{
    
    
    /// <summary>
    /// 实际值
    /// </summary>
    TrueValue,
    /// <summary>
    /// 按比例计算
    /// </summary>
    RadioValue
}
/// <summary>
/// 截屏对象
/// </summary>
public class ScreenCapture
{
    
    
    /// <summary>
    /// 截屏事件，每截取一帧都会回调
    /// </summary>
    public event EventHandler<ScreenCaptureDataEventArgs> Captured;
    /// <summary>
    /// 截屏开始时回调
    /// </summary>
    public event EventHandler<ScreenCaptureEventArgs> Started;
    /// <summary>
    /// 结束时回调
    /// </summary>
    public event EventHandler Stoped;
    /// <summary>
    /// 截屏是否已停止
    /// </summary>
    public bool IsStoped {
    
     private set; get; }
    /// <summary>
    /// 是否截取鼠标
    /// </summary>
    public bool IsPaintMouse {
    
     set; get; } = true;
    /// <summary>
    /// 截屏区域的计算方式
    /// TrueValue为实际值。RatioValue为比例值，范围0-1，全屏设为0,0,1,1，则无论任何设备任何分辨率都是截取全屏。
    /// </summary>
    public ScreenCaptureValueType ClipRectValueType {
    
     private set; get; } = ScreenCaptureValueType.RadioValue;
    /// <summary>
    /// 截屏区域X坐标
    /// </summary>
    public double ClipX {
    
     private set; get; } = 0;
    /// <summary>
    /// 截屏区域Y坐标
    /// </summary>
    public double ClipY {
    
     private set; get; } = 0;
    /// <summary>
    /// 截屏区域宽
    /// </summary>
    public double ClipWidth {
    
     private set; get; } = 1;
    /// <summary>
    /// 截屏区域高
    /// </summary>
    public double ClipHeight {
    
     private set; get; } = 1;
    /// <summary>
    /// 截屏帧率
    /// </summary>
    public double Framerate{
    
     set; get; }=30;
    /// <summary>
    /// 设置截屏区域
    /// </summary>
    /// <param name="x">x坐标</param>
    /// <param name="y">y坐标</param>
    /// <param name="width">宽</param>
    /// <param name="height">高</param>
    /// <param name="valueType">TrueValue为实际值。RatioValue为比例值，范围0-1，全屏设为0,0,1,1，则无论任何设备任何分辨率都是截取全屏。</param>
    public void SetClipRect(double x, double y, double width, double height, ScreenCaptureValueType valueType);
    /// <summary>
    /// 启动屏幕采集
    /// </summary>
    public void Start();
    /// <summary>
    /// 停止屏幕采集
    /// 异步方法，Stoped事件为真正的停止。
    /// </summary>
    public void Stop();
    /// <summary>
    /// 截取一帧图片
    /// </summary>
    /// <param name="x">x坐标</param>
    /// <param name="y">y坐标</param>
    /// <param name="width">宽</param>
    /// <param name="height">高</param>
    /// <param name="isPaintMouse">是否绘制鼠标</param>
    /// <returns>截屏后的位图对象，需要调用Dispose手动释放资源。</returns>
    public static System.Drawing.Bitmap Snapshot(int x, int y, int width, int height, bool isPaintMouse);

完整代码如下：
https://download.csdn.net/download/u013113678/71984470

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四、使用示例

1.截屏

xaml

<Window x:Class="WpfScreenCaptureGdi.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:WpfScreenCaptureGdi"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid Cursor="Cross">
        <Image x:Name="img"  ></Image>
    </Grid>
</Window>

cs

public MainWindow()
{
    
    
    InitializeComponent();
    var bm = ScreenCapture.Snapshot(0, 0, 1920, 1080, true);
    var wb = BitmapInterop.BitmapToWriteableBitmap(bm);
    img.Source = wb;
    bm.Dispose();
}

效果预览：

2.屏幕采集

示例一、显示桌面

xaml

<Window x:Class="WpfScreenCaptureGdi.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:WpfScreenCaptureGdi"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800"
        Closing="Window_Closing"
        >
    <Grid Cursor="Cross">
        <Image x:Name="img"  ></Image>
    </Grid>
</Window>

cs

ScreenCapture sc = new ScreenCapture();
public MainWindow()
{
    
    
    InitializeComponent();
    //注册事件
    sc.Captured += Sc_Captured;
    sc.Started += Sc_Started;
    //开始采集
    sc.Start();
}

private void Sc_Started(object sender, ScreenCaptureEventArgs e)
{
    
    
    Dispatcher.Invoke(() =>
    {
    
    
        //初始化位图对象    
        img.Source = BitmapInterop.CreateCompatibleWriteableBitmap(e.Width, e.Height, e.PixelFormat);
    });
}

private void Sc_Captured(object sender, ScreenCaptureDataEventArgs e)
{
    
    
    //采集的画面用于显示
    Dispatcher.Invoke(() =>
    {
    
    
        var wb = img.Source as WriteableBitmap;
        if (wb.Width < e.Width || wb.Height < e.Height)
        //宽高改变了重新初始化位图对象
        {
    
    
            wb = BitmapInterop.CreateCompatibleWriteableBitmap(e.Width, e.Height, e.PixelFormat);
            img.Source = wb;
        }
        wb.WritePixels(new Int32Rect(0, 0, e.Width, e.Height), e.Data, e.Length, e.Stride, 0, 0);
    });
}

private void Window_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
    
    
    //异步的方式退出才不会造成死锁
    if (!sc.IsStoped)
    {
    
    
        sc.Stop();
        sc.Stoped += (s, e) =>
        {
    
    
            Dispatcher.Invoke(() =>
            {
    
    
                Close();
            });
        };
        e.Cancel = true;
    }
}

示例二、动态调整参数

可以在采集过程中动态调整参数，比如采集区域、帧率、鼠标绘制。
在示例一的基础上添加如下代码：

//测试动态调整参数
var t = new Thread(() =>
  {
    
    
      while (true)
      {
    
    
          for (int i = 1; i <= 100; i++)
          {
    
    
              sc.SetClipRect(0, 0, i / 100.0, i / 100.0, ScreenCaptureValueType.RadioValue);
              Thread.Sleep(100);
          }
          for (int i = 1; i <= 1920; i++)
          {
    
    
              sc.SetClipRect(0, 0, i, 1080, ScreenCaptureValueType.TrueValue);
              Thread.Sleep(1);
          }
      }
  });
t.IsBackground = true;
t.Start();
//测试动态调整参数 --end

效果预览：

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总结

以上就是今天要讲的内容，本文简单介绍GDI+截屏的方法，添加鼠标的实现以及将GDI+对象转换成wpf对象，和屏幕采集的实现，总的来说不算是特别容易，原理很简单但是有不少细节需要处理，尤其是调试中出现资源释放问题，需要有c++开发的意识，才能很好的定位和解决问题。