X11 v-sync not working on Raspberry Pi with Avalonia (Screen Tearing Between Views)

[myrup]

Describe the bug

I'm experiencing heavy screen tearing in my Avalonia application running on a Raspberry Pi. The issue occurs when switching between views, where both views appear partially at the same time, causing a visible tear. Display can even get stuck in a rendered state between two views (usually teared around the horizontal centerline).

Interestingly, glxgears runs perfectly synchronized, but Avalonia does not, suggesting that Avalonia is not properly handling v-sync on my setup.

I prefer to run without without DRM because screenshotting tools is needed. I have been unable to find documentation on which flags I could experiment with to fix this.

To Reproduce

App without DRM:

public static AppBuilder BuildAvaloniaApp()
            => AppBuilder.Configure<App>()
                .UsePlatformDetect()
                .LogToTrace();

Expected behavior

No tearing

Avalonia version

11.2.2

OS

Linux

Additional context

No response

[myrup]

I have been unable to find updated information about the configuration of Avalonia X11 rendering engine options. If anyone can provide information on how to configure things like enabling/disabling GL, or v-sync related options it would be of great help for me towards debugging this.

[thevortexcloud]

As far as I am aware, the only options you get are these:

Avalonia/src/Avalonia.X11/X11Platform.cs

Line 263 in dd2c92c

public class X11PlatformOptions

Which you use by passing to the setup methods to start Avalonia (most likely in your main method), like this:

Avalonia/samples/XEmbedSample/Program.cs

Lines 13 to 24 in dd2c92c

	static void Main(string[] args)
	{
	HarfbuzzWorkaround.Apply();
	AppBuilder.Configure<App>()
	.UseSkia()
	.With(new X11PlatformOptions()
	{
	UseGLibMainLoop = true,
	ExterinalGLibMainLoopExceptionLogger = e => Console.WriteLine(e.ToString())
	})
	.UseX11()
	.SetupWithoutStarting();

[maxkatz6]

@kekekeks does X11 backend has v-sync timer? I don't see any special IRenderTimer implementations.

[myrup]

As far as I am aware, the only options you get are these:

Avalonia/src/Avalonia.X11/X11Platform.cs

Line 263 in dd2c92c

public class X11PlatformOptions
Which you use by passing to the setup methods to start Avalonia (most likely in your main method), like this:

Avalonia/samples/XEmbedSample/Program.cs

Lines 13 to 24 in dd2c92c

static void Main(string[] args)
{
HarfbuzzWorkaround.Apply();
AppBuilder.Configure()
.UseSkia()
.With(new X11PlatformOptions()
{
UseGLibMainLoop = true,
ExterinalGLibMainLoopExceptionLogger = e => Console.WriteLine(e.ToString())
})
.UseX11()
.SetupWithoutStarting();

Exactly the stuff I was looking for thanks 🙏! Further investigation pending, but I can confirm that (counterintuitively) forcing software rendering removes the worst tearing.

[kekekeks]

does X11 backend has v-sync timer? I don't see any special IRenderTimer implementations.

V-Sync and tearing prevention is expected to be provided by OpenGL implementation, not by timing your frames.
We might be missing some flag during GLX/EGL initialization

[kekekeks]

Try adding something like

using(context.EnsureCurrent())
     glXSwapIntervalEXT(context.Display, _info.Handle, 1);

here https://github.com/AvaloniaUI/Avalonia/blob/master/src/Avalonia.X11/Glx/GlxGlPlatformSurface.cs#L22