Doc - High-DPI support is now enabled by default in Chromium

[amaitland]

Starting in M108 High-DPI support is now enabled by default in Chromium.

Additionally, as a refactor to move responsibility out of the embedder
this change moves the existing EnableHighDPISupport calls in
chrome_exe_main_win.cc into the respective GpuMain &
BrowserMainRunnerImpl for the GPU & Browser processes.

chromiumembedded/cef#3452

[amaitland]

For WPF the default would appear to be still System aware, WPF must be setting that somewhere internally (which makes sense as that's the default that WPF uses). So setting via the app.manifest is still required.

[amaitland]

M111 will be the first version to rely on the Chromium default. The BrowserSubProcess no longer has app.manifest entries for DPI Awareness. Setting the DPI Awareness programmatically looks like it also influences the GPU process. See #2927 (comment)

[UweKeim]

I want to continue using CefSharp in a WinForms app that is currently not yet capable of running in High-DPI mode.

Is there still a way to fall back to non-High-DPI mode?

---

Update 1

It seems that disabling High-DPI through the application manifest did not help.

Instead, I removed all High-DPI related stuff from the manifest and instead did call the following right at the beginning of my application:

SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_UNAWARE);

So far, it seems that this works.

(Context: I'm using CefSharp as "self-hosted" in a .NET 7 WinForms application, 64-bit)

[Yokomoko]

I cannot seem to find this SetProcessDpiAwarenessContext method, do you know where this is? As I also need this.

[UweKeim]

@Yokomoko Sure, it is P/Invoke:

[DllImport(@"user32.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
public static extern bool SetProcessDpiAwarenessContext(IntPtr dpiAWarenessContext);

private const int DPI_AWARENESS_CONTEXT_UNAWARE = -1;
private const int DPI_AWARENESS_CONTEXT_UNAWARE_GDISCALED = -5;

My call then looks like:

var r = SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_UNAWARE);
if (!r)
{
    var error = Marshal.GetLastWin32Error();
    Trace.TraceWarning($@"Error settings DPI awareness: {error}.");
}

[jquerijero]

There is a bitmap scaling that is used by Terminal Server and newer Windows versions for non-DPI aware (manifest not modified) application. Chromium instance is overriding that function by re-rendering the application (including windows that doesn't contain an embedded browser) causing it to resize and remove bitmap scaling.

[amaitland]

Chromium instance is overriding that function by re-rendering the application

Chromium uses Per Monitor V2 by default.

You can override this behaviour as

Setting the DPI Awareness programmatically looks like it also influences the GPU process. See #2927 (comment)

There are some additional examples of setting DPI awareness programmatically.

[amaitland]

In the context of WinForms. Setting DPI Awareness via app.manifest is no longer recommended when using .Net 4.8 or greater (this includes newer versions including .Net 8.0).

See https://learn.microsoft.com/en-us/dotnet/desktop/winforms/wfdev-diagnostics/wfac010?view=netdesktop-8.0 for Microsoft guidance regarding the compiler warning that will be raised.

Starting in .Net Core 3.0 you can use the WinForms specific API. Some examples (refer to the Microsoft documentation for more details)

Application.SetHighDpiMode(HighDpiMode.DpiUnaware);
Application.SetHighDpiMode(HighDpiMode.DpiUnawareGdiScaled);
Application.SetHighDpiMode(HighDpiMode.SystemAware);
Application.SetHighDpiMode(HighDpiMode.PerMonitor);
Application.SetHighDpiMode(HighDpiMode.PerMonitorV2);

https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.application.sethighdpimode?view=windowsdesktop-8.0