message: cmgen: add support for non-RLE HDR images.
  The new conditional is cribbed from STB, which checks the first three
  bytes.
  Fixes
diff: @@ -370,28 +370,34 @@ LinearImage HDRDecoder::decode() {
  if (sx == '-') image = horizontalFlip(image);
  if (sy == '+') image = verticalFlip(image);
  - uint16_t w;
  - uint16_t magic;
  + // Allocate memory to hold one row of decoded pixel data.
  std::unique_ptr<uint8_t[]> rgbe(new uint8_t[width * 4]);
  - if (width < 8 || width > 32767) {
  + // First, test for non-RLE images.
  + const auto pos = mStream.tellg();
  + mStream.read((char*) rgbe.get(), 3);
  + mStream.seekg(pos);
  +
  + if (rgbe[0] != 0x2 || rgbe[1] != 0x2 || (rgbe[2] & 0x80) || width < 8 || width > 32767) {
  for (uint32_t y = 0; y < height; y++) {
  - filament::math::float3* i = reinterpret_cast< filament::math::float3*>(image.getPixelRef(0, y));
  - mStream.read((char*) &rgbe, width * 4);
  + filament::math::float3* dst = reinterpret_cast<filament::math::float3*>(image.getPixelRef(0, y));
  + mStream.read((char*) rgbe.get(), width * 4);
  // (rgb/256) * 2^(e-128)
  size_t pixel = 0;
  for (size_t x = 0; x < width; x++, pixel += 4) {
  filament::math::float3 v(rgbe[pixel], rgbe[pixel + 1], rgbe[pixel + 2]);
  - i[x] = v * std::ldexp(1.0f, rgbe[pixel + 3] - (128 + 8));
  + dst[x] = v * std::ldexp(1.0f, rgbe[pixel + 3] - (128 + 8));
  }
  }
  } else {
  for (uint32_t y = 0; y < height; y++) {
  - //std::cout << "line: " << y << std::endl;
  + uint16_t magic;
  mStream.read((char*) &magic, 2);
  if (magic != 0x0202) {
  throw std::runtime_error("invalid scanline (magic)");
  }
  +
  + uint16_t w;
  mStream.read((char*) &w, 2);
  if (ntohs(w) != width) {
  throw std::runtime_error("invalid scanline (width)");
  @@ -424,11 +430,11 @@ LinearImage HDRDecoder::decode() {
  uint8_t const* g = &rgbe[width];
  uint8_t const* b = &rgbe[2 * width];
  uint8_t const* e = &rgbe[3 * width];
  - filament::math::float3* i = reinterpret_cast< filament::math::float3*>(image.getPixelRef(0, y));
  + filament::math::float3* dst = reinterpret_cast<filament::math::float3*>(image.getPixelRef(0, y));
  // (rgb/256) * 2^(e-128)
  for (size_t x = 0; x < width; x++, r++, g++, b++, e++) {
  filament::math::float3 v(r[0], g[0], b[0]);
  - i[x] = v * std::ldexp(1.0f, e[0] - (128 + 8));
  + dst[x] = v * std::ldexp(1.0f, e[0] - (128 + 8));
  }
  }
  }
  