c++ - Targa Run-Length encoding -


i trying decompress targa (rgb24_rle) image data.

my algorithm looks this:

static constexpr size_t kpacketheadersize = sizeof(char);          //http://paulbourke.net/dataformats/tga/         inline void decompressrle(unsigned int a_byteperpixel, std::vector<crbyte>& a_in, std::vector<crbyte>& a_out)         {             (auto = a_in.begin(); != a_in.end();)             {                 //read packet header                 int header = *it & 0xff;                 int count = (header & 0x7f) + 1;                  if ((header & 0x80) != 0) //packet type                 {                     //for run length packet, header followed                     //a single color value, assumed repeated                     //the number of times specified in header.                      auto pastart = + kpacketheadersize;                     auto paend = pastart + a_byteperpixel;                      //insert packets output buffer                     (size_t pk = 0; pk < count; ++pk)                     {                         a_out.insert(a_out.end(), pastart, paend);                     }                      //jump next header                     std::advance(it, kpacketheadersize + a_byteperpixel);                 }                 else                 {                     //for raw packet, header s followed                     //the number of color values specified in header.                      auto pastart = + kpacketheadersize;                     auto paend = pastart + count * a_byteperpixel;                      //insert packets output buffer                     a_out.insert(a_out.end(), pastart, paend);                      //jump next header                     std::advance(it, kpacketheadersize + count * a_byteperpixel);                 }             }         }

it called here:

//read compressed data std::vector<crbyte> compressed(imagesize); ifs.seekg(sizeof(header), std::ifstream::beg); ifs.read(reinterpret_cast<char*>(compressed.data()), imagesize);  //decompress std::vector<crbyte> decompressed(imagesize); decompressrle(byteperpixel, compressed, decompressed);

imagesize defined this:

size_t imagesize = hd.width * hd.height * byteperpixel

however, after decompressrle() finishes (which takes very long time 2048x2048 textures) decompressed still empty/only contains zeros. maybe missing somehting out.

count seems unreasonably high sometimes, think abnormal. compressedsize should less imagesize, otherwise it's not compressed. however, using ifstream::tellg() gives me wrong results. help?

if @ variables in debugger, see std::vector<crbyte> decompressed(imagesize); declares vector imagesize elements in it. in decompressrle insert @ end of vector, causing grow. why decompressed image full of zeros, , why takes long (because vector resized periodically).

what want reserve space:

std::vector<crbyte> decompressed; decompressed.reserve(imagesize);

your compressed buffer looks larger file content, you're still decompressing past end of file. compressed file size should in header. use it.


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