Function prepareTextureChannel

src/Image.cpp:782–824

template <typename T>
Task<void> prepareTextureChannel(T* data, const Channel* chan, Box2i box, size_t channelIdx, size_t numTextureChannels) {
    const bool isAlpha = channelIdx == 3 || (chan && Channel::isAlpha(chan->name()));
    const T defaultVal = isAlpha ? (T)1.0f : (T)0.0f;

    const auto size = box.size();
    const size_t numPixels = posProd(size);

    if (chan) {
        const auto copyChannel = [&](const auto view) -> Task<void> {
            co_await ThreadPool::global().parallelFor(
                0,
                size.y(),
                numPixels,
                [view, &data, numTextureChannels, channelIdx, width = size.x(), pos = box.min](int y) {
                    for (int x = 0; x < width; ++x) {
                        const auto tileIdx = x + y * (size_t)width;
                        data[tileIdx * numTextureChannels + channelIdx] = view[pos.x() + x, pos.y() + y];
                    }
                },
                numeric_limits<int>::max()
            );
        };

        switch (chan->pixelFormat()) {
            case EPixelFormat::U8: co_await copyChannel(chan->view<const uint8_t>()); break;
            case EPixelFormat::U16: co_await copyChannel(chan->view<const uint16_t>()); break;
            case EPixelFormat::U32: co_await copyChannel(chan->view<const uint32_t>()); break;
            case EPixelFormat::I8: co_await copyChannel(chan->view<const int8_t>()); break;
            case EPixelFormat::I16: co_await copyChannel(chan->view<const int16_t>()); break;
            case EPixelFormat::I32: co_await copyChannel(chan->view<const int32_t>()); break;
            case EPixelFormat::F16: co_await copyChannel(chan->view<const half>()); break;
            case EPixelFormat::F32: co_await copyChannel(chan->view<const float>()); break;
        }
    } else {
        co_await ThreadPool::global().parallelFor(
            0uz,
            numPixels,
            numPixels,
            [&data, defaultVal, numTextureChannels, channelIdx](size_t j) { data[j * numTextureChannels + channelIdx] = defaultVal; },
            numeric_limits<int>::max()
        );
    }
}

Texture* Image::texture(span<const string> channelNames, EInterpolationMode minFilter, EInterpolationMode magFilter) & {
    if (size().x() > maxTextureSize() || size().y() > maxTextureSize()) {