Function FillMaterialTranscodeMapping

samples/renderer/NtcMaterialLoader.cpp:178–343

}

static void FillMaterialTranscodeMapping(NtcMaterial& material, ntc::ITextureSetMetadata* textureSetMetadata,
    MaterialChannelMap const& channelMap, bool onlyAlphaMask)
{
    // Derive the valid channel mask from the shuffle map, because textureSetMetadata->GetValidChannelMask()
    // returns "1" bits for constant channels, and we want to know where actual textures exist.
    uint32_t channelMask = 0;
    for (int ch = 0; ch < NTC_MAX_CHANNELS; ++ch)
    {
        if (channelMap.swizzle[ch].type == ntc::ShuffleSourceType::Channel)
            channelMask |= (1 << ch);
    }

    // If we only need to create the alpha mask texture, see if the material actually needs an alpha mask
    // and if the NTC texture set has an alpha mask channel.
    if (onlyAlphaMask)
    {
        // Test the channel mask for the presence of opacity channel.
        // Note: not testing the material domain because in some cases, one texture set can be reused
        // for multiple materials with different domains, and we cache and reuse the transcode mapping.
        // One model with such reuse is AlphaBlendModeTest from the Khronos glTF sample asset collection.
        bool opacityChannelPresent = TextureSetHasChannels(channelMask, CHANNEL_OPACITY, 1);

        if (!opacityChannelPresent)
            return;

        TextureTranscodeTask& opacityTexture = material.transcodeMapping.emplace_back();
        opacityTexture.bcFormat = ntc::BlockCompressedFormat::BC4;
        opacityTexture.nvrhiBcFormat = nvrhi::Format::BC4_UNORM;
        opacityTexture.firstChannel = CHANNEL_OPACITY;
        opacityTexture.numChannels = 1;
        opacityTexture.pMaterialTexture = &NtcMaterial::opacityTexture;
        opacityTexture.pFeedbackTexture = &NtcMaterial::opacityTextureFeedback;
        opacityTexture.name = "Opacity";
    }
    else
    {
        if (TextureSetHasChannels(channelMask, CHANNEL_BASE_COLOR, 3))
        {
            TextureTranscodeTask& baseColorTexture = material.transcodeMapping.emplace_back();
            baseColorTexture.bcFormat = ntc::BlockCompressedFormat::BC7;
            baseColorTexture.nvrhiBcFormat = nvrhi::Format::BC7_UNORM_SRGB;
            baseColorTexture.firstChannel = CHANNEL_BASE_COLOR;
            baseColorTexture.numChannels = TextureSetHasChannels(channelMask, CHANNEL_OPACITY, 1) ? 4 : 3;
            static_assert(CHANNEL_OPACITY == CHANNEL_BASE_COLOR + 3);
            baseColorTexture.sRGB = true;
            baseColorTexture.pMaterialTexture = &NtcMaterial::baseOrDiffuseTexture;
            baseColorTexture.pFeedbackTexture = &NtcMaterial::baseOrDiffuseTextureFeedback;
            baseColorTexture.name = "BaseColor";
        }
        
        if (material.useSpecularGlossModel)
        {
            if (TextureSetHasChannels(channelMask, CHANNEL_SPECULAR_COLOR, 3))
            {
                TextureTranscodeTask& specularTexture = material.transcodeMapping.emplace_back();
                specularTexture.bcFormat = ntc::BlockCompressedFormat::BC7;
                specularTexture.nvrhiBcFormat = nvrhi::Format::BC7_UNORM_SRGB;
                specularTexture.firstChannel = CHANNEL_SPECULAR_COLOR;