Method unpackAndSave422

tools/ktx/command_extract.cpp:546–707

using namespace imageio;

void CommandExtract::unpackAndSave422(std::string filepath, bool appendExtension,
        VkFormat vkFormat, const FormatDescriptor& format, uint32_t width, uint32_t height,
        const char* data, std::size_t size) {
    (void) vkFormat;

    assert(format.model() == KHR_DF_MODEL_YUVSDA);
    assert(format.find(KHR_DF_CHANNEL_YUVSDA_Y));
    // Create a custom format with the same precision but with only 3 channels
    // Reuse similar 4 channel VkFormats and drop the last channel (There is no RGB variant of 10X6 and 12X4)
    const auto precision = format.find(KHR_DF_CHANNEL_YUVSDA_Y)->bitLength + 1u;
    auto unpackedFormat = createFormatDescriptor(
            precision == 8 ? VK_FORMAT_R8G8B8A8_UNORM :
            precision == 10 ? VK_FORMAT_R10X6G10X6B10X6A10X6_UNORM_4PACK16 :
            precision == 12 ? VK_FORMAT_R12X4G12X4B12X4A12X4_UNORM_4PACK16 :
            precision == 16 ? VK_FORMAT_R16G16B16A16_UNORM :
            VK_FORMAT_UNDEFINED, *this);
    unpackedFormat.removeLastChannel();

    // 1 pixel (block) with 4 channel is unpacked to 2 pixel with 3 channels: Y0,Y1,U,V -> R0,G0,B0,R1,G1,B1
    const auto blockYUVBytes = format.pixelByteCount();
    const auto blockDimensionX = format.basic.texelBlockDimension0 + 1;
    const auto blockDimensionY = format.basic.texelBlockDimension1 + 1;
    const auto pixelBytes = unpackedFormat.pixelByteCount();
    const auto channelBytes = pixelBytes / 3;
    assert(format.sampleCount() == 4);
    assert(format.basic.texelBlockDimension0 + 1 == 2);
    assert(format.basic.texelBlockDimension1 + 1 == 1);
    assert(format.basic.texelBlockDimension2 + 1 == 1);
    assert(format.basic.texelBlockDimension3 + 1 == 1);
    assert(size == width * height * blockYUVBytes / blockDimensionX / blockDimensionY);
    (void) size;
    (void) blockDimensionY;

    uint32_t y0Offset = 0;
    uint32_t y0Bits = 0;
    uint32_t y0PositionX = 0;
    uint32_t y1Offset = 0;
    uint32_t y1Bits = 0;
    uint32_t y1PositionX = 0;
    uint32_t uOffset = 0;
    uint32_t uBits = 0;
    uint32_t uPositionX = 0;
    uint32_t vOffset = 0;
    uint32_t vBits = 0;
    uint32_t vPositionX = 0;

    for (const auto& sample : format.samples) {
        switch (sample.channelType) {
        case KHR_DF_CHANNEL_YUVSDA_Y:
            if (y0Bits != 0) {
                y1Offset = sample.bitOffset;
                y1Bits = sample.bitLength + 1;
                y1PositionX = sample.samplePosition0;
            } else {
                y0Offset = sample.bitOffset;
                y0Bits = sample.bitLength + 1;
                y0PositionX = sample.samplePosition0;
            }