CODEWITHSUNDEEP
camerapreviewms-media-foundation
radimoid
radimoid

Reputation: 199

Clear preview window in media foundation

Is it possible to clear a preview window after preview from camera is done? I am using MFCaptureEngine, calling m_pPreview->SetRenderHandle(m_hwnd) to render the video. But when I stop the video I am not able to draw on the window. There remains a last frame from the camera. I need to fill the window by black brush and draw some text, but the image from the camera cannot be overdrawn.

Upvotes: 1

Views: 811

Answers (2)

radimoid
radimoid

Reputation: 199

I've implemented it this way:

// Sink
CComPtr<IMFCaptureSink> pSink;
m_pEngine->GetSink(MF_CAPTURE_ENGINE_SINK_TYPE_PREVIEW, &pSink);

CComPtr<IMFMediaSink> pCustomSink;
::MFCreateVideoRenderer(IID_IMFMediaSink, (void**)&pCustomSink);

CComPtr<IMFCapturePreviewSink> pPreviewSink;
pSink.QueryInterface(&pPreviewSink);
pPreviewSink->SetCustomSink(pCustomSink);

// preview
pSink.QueryInterface(&m_pPreview); // or pPreviewSink.QueryInterface(&m_pPreview)
m_pPreview->SetRenderHandle(m_hwndPreview);

But the behaviour is still the same (the screen cannot be redrawn after the preview is stopped).

Upvotes: 0

Evgeny Pereguda
Evgeny Pereguda

Reputation: 583

It is not clear understand from you answer what is it MFCaptureManager, but by code SetRenderHandle(m_hwnd) I see that you use IMFCapturePreviewSink::SetRenderHandle. So, I can say that I had faced with similar problem some time ago, and it is related with difference between of the old window system which exist from WinXP and current window system from Vista. Code sets window context to the renderer by calling IMFCapturePreviewSink::SetRenderHandle - for IMFCapturePreviewSink it is DirectX11 - and DirectX11 has got FULL access to the window and it is switched to current window system. As a result, any calling fill the window by black brush and draw some text which is done by old Windows API from Win95-XP generation do nothing - because window handler context is LOCKED by DirectX11.

There are three ways for resolving of this problem:

  1. Write the new UI by the new Microsoft DirectComposition GUI API which is based on DirectX11 and set it to IMFCapturePreviewSink::SetRenderSurface.
  2. Create EVR Media Sink by MFCreateVideoRenderer - it creates DirectX9 video renderer which is compatible with old Windows API from Win95-XP generation, and set this IMFMediaSink in IMFCapturePreviewSink::SetCustomSink.
  3. Create code of the video renderer on DirectX9 base - for example MFCaptureD3D/device.cpp, and draw raw IMFSample from callback IMFCapturePreviewSink::SetSampleCallback.

Regards.

Upvotes: 1

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