WPF flickering behaviour

[bforl]

I have a simple scene that basically just renders a load of cubes. When I run this scene as part of a Vortice.Framework.D3D11Application (i.e not WPF) it runs fine, no flickering.

However, when I use the same code in a WPF app, using the DrawingSurface helper, I get very bad flickering. Which is 100x time worse when running in Release. In Debug, its only very rarely happens (I wasn't able to capture it in the video below)

I have enabled native debugging (and made sure I have the Graphs Tools enabled), and don't seem to get any DX warnings or errors, so I think the code is all fine.

It's almost as if WPF is sometimes displaying the image buffer half way through the rendering process (i.e half way between the total draw calls). The reason I say this, is because the ClearRenderTargetView colour is set to Red, and its mostly a red flickering background, as if it has only rendered a small number of cubes.

Any ideas?

[Debug Build] (No issues)

2025-01-11.19-12-01.mp4

[Release Build] (Flickering)

2025-01-11.19-08-06.mp4

[amerkoleci]

Hi,
Can you release a repro project?

[bforl]

Hi, here is an example case. https://github.com/bforl/Vortice_Flickering

On my machine this flickers badly (when compiling in release)

I think it is very much dependant on the amount of work being done and the power of your GPU. In my case, it is onboard graphics.

If you have an actual GPU, you'll probably need to wack up the number of objects being rendered (in DrawingSurface_LoadContent)

[bforl]

Having done a little research on this, it seems like its a very common problem and existed with SharpDX and SlimDX. Although, the fixes suggested seem to vary.

I have now manged to get it flicker free, by applying the following two changes

[Change 1]
As ImmediateContext.Flush is asynchronous, and so will return before completion, you have to wait on a query in DrawingSurface

private void Render()
{
	if (_device == null || _deviceContext == null || ColorTexture == null)
		return;

	_deviceContext.OMSetRenderTargets(ColorTextureView!, DepthStencilView);
	_deviceContext.RSSetViewport(0, 0, TextureWidth, TextureHeight);
	_deviceContext.RSSetScissorRect(0, 0, TextureWidth, TextureHeight);

	RaiseDraw(new DrawEventArgs(this, _device!, _deviceContext!));

	_device.ImmediateContext.Flush();


       // *************************

	using var query = _device.CreateQuery(QueryType.Event, QueryFlags.None);

	// mark completion of drawing operations
	_deviceContext.End(query);

	// wait until drawing completes
	while (!(_deviceContext.GetData(query, out RawBool completed) && completed))
	{
		Thread.Yield();
	}
}

[Change 2]
It seems like you have to lock the D3D11ImageSource around the rendering. (this was mentioned in the last post here https://stackoverflow.com/questions/27358128/d3dimage-and-sharpdx-flickering-on-slow-hardware)

DrawingSurface

	private void OnRendering(object? sender, EventArgs e)
	{
		if (!_isRendering)
			return;

		if (_contentNeedsRefresh || AlwaysRefresh)
		{
			if (_d3dSurface!._TryLock())
			{
				Render();
				_d3dSurface._Unlock();
			}
		}
	}

D3D11ImageSource

//internal void InvalidateD3DImage()
//{
//	if (_renderTarget == null)
//		return;

//	Lock();
//	AddDirtyRect(new Int32Rect(0, 0, PixelWidth, PixelHeight));
//	Unlock();
//}

public bool _TryLock()
{
	TimeSpan timeout = TimeSpan.FromMilliseconds(100);

	if (_renderTarget == null)
		return false;

	return TryLock(timeout);
}

public void _Unlock()
{
	AddDirtyRect(new Int32Rect(0, 0, PixelWidth, PixelHeight));
	Unlock();
}