如何使用 CopyFromScreen 在 WPF Window 中创建 win32 控件的图像

Question

I want to create an image from a win32 control (ie WindowsFormsHost, Hwndhost, webview2) being displayed in a WPF window.

1. Am I correct that RenderTargetBitmap will not work for these kinds of controls?

Assuming I am correct, I am looking at the methods used in this GitHub project to make the image. The project wraps the webbrowser control in a ContenControl. It then gets the position of this content control on the screen and uses the Graphics class method CopyFromScreen.

private void CreateScreenshotFromContent()
{
    Point upperLeftPoint = _airspaceContent.PointToScreen(new Point(0, 0));
    var bounds = new System.Drawing.Rectangle((int)(upperLeftPoint.X * _scalingFactor),
                                              (int)(upperLeftPoint.Y * _scalingFactor),
                                              (int)(_airspaceContent.RenderSize.Width * _scalingFactor),
                                              (int)(_airspaceContent.RenderSize.Height * _scalingFactor));

    using (var bitmap = new System.Drawing.Bitmap((int)bounds.Width, (int)bounds.Height))
    {
        using (var g = System.Drawing.Graphics.FromImage(bitmap))
        {
            g.CopyFromScreen(new System.Drawing.Point(bounds.Left, bounds.Top),
                             System.Drawing.Point.Empty,
                             new System.Drawing.Size((int)bounds.Width, (int)bounds.Height));
        }

        _airspaceScreenshot.Source = GetImageSourceFromBitmap(bitmap);
    }
}

// https://stackoverflow.com/questions/5977445/how-to-get-windows-display-settings
[DllImport("gdi32.dll")]
static extern int GetDeviceCaps(IntPtr hdc, int nIndex);
private void GetScalingFactor()
{
    var g = System.Drawing.Graphics.FromHwnd(IntPtr.Zero);
    IntPtr desktop = g.GetHdc();
    int LogicalScreenHeight = GetDeviceCaps(desktop, 10);
    int PhysicalScreenHeight = GetDeviceCaps(desktop, 117);

    float ScreenScalingFactor = (float)PhysicalScreenHeight / (float)LogicalScreenHeight;

    _scalingFactor = ScreenScalingFactor; // 1.25 = 125%
}

public ImageSource GetImageSourceFromBitmap(System.Drawing.Bitmap bitmap)
{
    using (var memory = new MemoryStream())
    {
        bitmap.Save(memory, ImageFormat.Png);
        memory.Position = 0;
        BitmapImage bitmapImage = new BitmapImage();
        bitmapImage.BeginInit();
        bitmapImage.StreamSource = memory;
        bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
        bitmapImage.EndInit();
        return bitmapImage;
    }
}

The GitHub project uses the WebBrowser control. One small complication is I am updating this to the WebView2 control which is newer but is also just a win32 control in WPF.

All works fine if the PC's scaling is 100%. The resulting image almost perfectly matches what the control displays. Unfortunately this does not if scaling is changed.

This is how the window looks with the Webbrowser control with 200% scaling.

The image however is considerable enlarged when the scaling is 200%.

My project now targets 4.7.2.Net Framework which if I understand correctly means it is now DPI aware thus I understand I do not need to do anything extra with the app config or manifest. Am I correct Manifest changes like below are no longer needed?

<application xmlns="urn:schemas-microsoft-com:asm.v3">
  <windowsSettings>
    <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
    <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true/pm</dpiAware>
  </windowsSettings>
</application>

Answer 1

Assuming _scalingFactor is problematic, I would recommend to use VisualTreeHelper.GetDpi method. In this case, GetScalingFactor method will be like the following:

public void GetScalingFactor()
{
    _scalingFactor = (float)VisualTreeHelper.GetDpi(_airspaceContent).DpiScaleX;
}

I think this class has much room for refactoring though.