DirectX flickering video

Question

Alright, so I wrote a custom VMR9 Allocator/Presenter which seems to work fine. However, when I attempt to copy video frames from the Allocator/Presenter surfaces into my application surfaces, the video appears to flicker. Audio playback is fine so I'm fairly certain it's not an issue of the machine being bogged down or anything. This is the code I have in my render loop.

g_pd3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_ARGB(255, 0, 0, 0), 1.0f, 0);

// render the scene
if (SUCCEEDED(g_pd3dDevice->BeginScene()))
{
//g_pd3dDevice->SetRenderTarget(0, g_pd3dSurface);

g_pd3dDevice->StretchRect(vmr9_ap->renderSurface, src, g_pd3dSurface, dest, D3DTEXF_NONE);

    // end the scene
    g_pd3dDevice->EndScene();
}

However, if I change it to this (commenting out clearing the buffer)

// g_pd3dDevice->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_ARGB(255, 0, 0, 0), 1.0f, 0);

// render the scene
if (SUCCEEDED(g_pd3dDevice->BeginScene()))
{
//g_pd3dDevice->SetRenderTarget(0, g_pd3dSurface);

g_pd3dDevice->StretchRect(vmr9_ap->renderSurface, src, g_pd3dSurface, dest, D3DTEXF_NONE);

    // end the scene
    g_pd3dDevice->EndScene();
}

this flickering goes away. I'm worried that this is somehow bad form/hackish and might cause more problems than it solves. Does anyone have any experience in this area? Is there a better solution?

Thanks!

Answer 1

If you intend to repaint the entire viewport every frame there is no reason to do a clear, and it can actually yield a lot of performance gains, so go for it! As for your flickering, that might be something different. Are you doing you're drawing in a WM_PAINT message? If so, you may want to also intercept the WM_ERASEBKGND message and simply return 1 when you get it. This prevents windows from trying to erase the background and has helped me get rid of some flickering in the past.

FYI: Ever do the noclip cheat in Doom or Quake, and when you walk outside a wall everything starts leaving "trails" all over? That's because they're not clearing the back buffer, since under normal circumstances the entire scene would be redrawn every time anyway. I say if it's good enough for id it's good enough for me! :)

Edit: Oh, and on more thing! I'm not sure if it's required or not, but I always do my clear AFTER calling BeginScene(). Could also be contributing to your flicker.

Answer 2

TBH i reckon you are best off writing your own directshow render filter that copies the data directly to a texture and then drawing a quad over the screen with the texture. You'd get much better performance. Writing a render filter is actually pretty easy. Especially when you appreciate you don't have to expose it to the operating system so most of the difficult DirectShow hurdles don't need t be jumped.

Edit: Look up the "Dump Filter" it comes as part of Microsoft's DirectShow helper code ...