PackedBitfield.hpp

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#pragma once
 
#include <Gfx/Graph/decoders/GPUVideoDecoder.hpp>
#include <Gfx/Graph/decoders/RGBA.hpp>
 
#include <QString>
 
namespace score::gfx
{
 
struct BitField
{
  int offset{}; 
  int width{};  
};
 
struct PackedBitfieldLayout
{
  int containerBytes{2}; 
  bool bigEndian{false}; 
  BitField r, g, b, a;
};
 
inline QString packedBitfieldFilter(const PackedBitfieldLayout& l)
{
  QString word;
  if(l.containerBytes == 1)
  {
    word = "uint(tex.r * 255.0 + 0.5)";
  }
  else
  {
    // tex.r is the first byte in memory, tex.g the second.
    word = l.bigEndian
               ? "(uint(tex.r * 255.0 + 0.5) << 8) | uint(tex.g * 255.0 + 0.5)"
               : "(uint(tex.g * 255.0 + 0.5) << 8) | uint(tex.r * 255.0 + 0.5)";
  }
 
  auto chan = [](const BitField& f) -> QString {
    if(f.width <= 0)
      return "1.0";
    const unsigned mask = (1u << f.width) - 1u;
    return QString("float((w >> %1) & %2u) / %3.0")
        .arg(f.offset)
        .arg(mask)
        .arg(mask);
  };
 
  return QString("uint w = %1;"
                 "processed.rgba = vec4(%2, %3, %4, %5);")
      .arg(word)
      .arg(chan(l.r))
      .arg(chan(l.g))
      .arg(chan(l.b))
      .arg(chan(l.a));
}
 
inline std::unique_ptr<GPUVideoDecoder>
makePackedBitfieldDecoder(const PackedBitfieldLayout& l, Video::ImageFormat& d)
{
  return std::make_unique<PackedDecoder>(
      l.containerBytes == 1 ? QRhiTexture::R8 : QRhiTexture::RG8,
      l.containerBytes, d, packedBitfieldFilter(l), /*invertY=*/false,
      /*nearest=*/true);
}
 
} // namespace score::gfx