Wrong Implementation of GetBackgroundColor in WicAnimatedGif

[maj113]

Windows-classic-samples/Samples/Win7Samples/multimedia/wic/wicanimatedgif/WicAnimatedGif.cpp

Line 915 in 2b94df5

HRESULT DemoApp::GetBackgroundColor(

/grctlext/TransparentColorIndex should be used to check if it's transparent instead of dwBGColor >> 24

Fixed version:

Without fix:

GIF from: https://en.tankiwiki.com/images/en/3/33/Preview_Disco_2.0.gif both in the browser and irfanview it shows as having a transparent BG

[fafalone]

How do you mean?

I did a check for if TransparentColorIndex == backgroundIndex then zero alpha, but can all gifs be guaranteed to not have a TransparentColorIndex with nonzero alpha?

        FLOAT alpha = (dwBGColor >> 24) / 255.f;

        hr = pMetadataQueryReader->GetMetadataByName(
            L"/grctlext/TransparentColorIndex",
            &propVariant);
        if (SUCCEEDED(hr))
        { 
            hr = (propVariant.vt != VT_UI1) ? E_FAIL : S_OK;
            if (SUCCEEDED(hr))
            {
                if (backgroundIndex == propVariant.bVal)
                {
                    alpha = 0.f;
                }
            }
            PropVariantClear(&propVariant);
        }