Transcode was not successful

[onepiecefreak]

Following my initial and first problem with PVRTexTool here: PVRTexLib in C# (with C++ tests)
I come across another problem separate to the one linked above.

I try to transcode an image from RGBA8888 to R8. This has no special meaning and is meant to serve as an example for me to learn how I set up the transcoder options.

I currently set up my options like this:

PVRTexLib_TranscoderOptions* CreateOptions()
{
    auto options = new PVRTexLib_TranscoderOptions();

    options->sizeofStruct = 0x2c;
    options->doDither = false;
    options->colourspace = PVRTexLibColourSpace::PVRTLCS_Linear;
    options->maxRange = 1;
    options->pixelFormat = PVRTexLibPixelFormat::R8;
    options->quality = PVRTexLibCompressorQuality::PVRTLCQ_PVRTCHigh;

    options->channelType[0] = { PVRTexLibVariableType::PVRTLVT_UnsignedByte };
    options->channelType[1] = { PVRTexLibVariableType::PVRTLVT_UnsignedByte };
    options->channelType[2] = { PVRTexLibVariableType::PVRTLVT_UnsignedByte };
    options->channelType[3] = { PVRTexLibVariableType::PVRTLVT_UnsignedByte };

    return options;
}

The PixelFormat R8 is setup as the value 0x0000000861626772, which defines the rgba encoding, where only the R channel is defined with 8 bits. This could already be a potential problem in why the Transcode may fail.

I would like someone to tell me if the options are correctly set up like this on first glance. I will reply with my full sample application code.

[onepiecefreak]

int main()
{
    auto data = new char[16*4];
    for (int i = 0; i < 16*4; i++)
        data[i] = 0;

    auto attribs = CreateParams();
    auto header = PVRTexLib_CreateTextureHeader(attribs);
    auto texture = PVRTexLib_CreateTexture(header, data);

    // Transcode texture
    auto options = CreateOptions();    // See CreateOptions method in my initial post
    auto successful = PVRTexLib_TranscodeTexture(texture, *options);
}

PVRHeader_CreateParams* CreateParams()
{
    PVRHeader_CreateParams* params = new PVRHeader_CreateParams();

    params->width = 4;
    params->height = 4;
    params->depth = 1;

    // Setting to zero means library will not use and/or print height/width information
    params->numMipMaps = 1;

    // Additionally to numMipMaps, if any of the number values is 0, PVRTexLib_GetTextureDataPtr will return 0
    params->numArrayMembers = 1;
    params->numFaces = 1;
    params->pixelFormat = PVRTexLibPixelFormat::RGBA8888;
    params->colourSpace = PVRTexLibColourSpace::PVRTLCS_Linear;
    params->channelType = PVRTexLibVariableType::PVRTLVT_UnsignedByte;
    params->preMultiplied = false;

    return params;
}

R8 is set up as 0x0000000861626772.
RGBA8888 is set up as 0x0808080861626772.

[AlejandroCosin]

Hi onepiecefreak,

Thanks for your interest in PVRTexTool. I’ll forward your questions to the Tools Team and come back to you shortly.

Best regards,
Alejandro

[AlejandroCosin]

Hi onepiecefreak,

The Tools Team has reviewed your issue.

The call to PVRTexLib_TranscodeTexture is failing due to passing the pixel format with a named channel (R/G/B/A) with a bit width of 0, which is not supported.

You have two options here:
1. Use the correct encoding for R8 which is 0x800000072.
2. Use the macro PVRTGENPIXELID defined in PVRTexLibDefines.h to create uncompressed pixel format IDs in a more straightforward way.

Best regards,
Alejandro

[onepiecefreak]

Oh, interesting. I thought I had to always give all color components and then just set their bit depth to zero, if they are not needed.

Thanks for the tip with the PVRTGENPIXELID macro. I will try that out and report back.

[onepiecefreak]

Yes, that worked. Thank you.

[AlejandroCosin]

Hi onepiecefreak,

Glad it worked, please come back if you have more questions.

Best regards,
Alejandro