BMPImage.hpp

#pragma once

#include "Image.hpp"
#include "File.hpp"
#include "Debug.hpp"
#include "Logger.hpp"

// https://stackoverflow.com/a/20596072/4811285
namespace img {
struct BMPImage : public Image {
  BMPImage(const char *filename):
    Image(filename)
  {
    init();
  }

  void init() {
    unsigned char header[138];
    size_t data_pos, img_size;

    // Open the file
    FILE *file = fopen(filename.c_str(),"rb");
    if(file == nullptr) {
      TERMINATE("bmp: unable to open file '%s'\n", filename.c_str());
    }

    sys::File::Lock fl(file);

    // If less than 54 bytes are read, problem
    size_t r;
    if((r = fread(header, sizeof(unsigned char), 138, file)) != 138) {
      TERMINATE("bmp: unable to read header of file '%s', length %lu\n", filename.c_str(), r);
    }

    // file signature
    ASSERT(header[0] == 'B' && header[1] == 'M');

    // make sure this is a 24bpp file
    ASSERT(*(int32_t*)&(header[0x1E]) == 0);
    if(*(int32_t*)&(header[0x1C]) != 24) {
      TERMINATE("bmp: required RGB image (24bpp)\n");
    }

    data_pos = *(int32_t*)&(header[0x0A]);
    img_size = *(int32_t*)&(header[0x22]);
    width = *(int32_t*)&(header[0x12]);
    height = *(int32_t*)&(header[0x16]);

    size_t bpp = 3;
    format = Image::Format::RGB;
    // Some BMP files are misformatted, guess missing information
    if(img_size == 0 || img_size != width * height * bpp) {
      Logger::Warning("[bmp] warning: file [%s] has incorrect img_size %d\n", filename.c_str(), img_size);
      img_size = width * height * bpp;
    }
    if(data_pos != 138) {
      Logger::Warning("[bmp] warning: file [%s] has incorrect data_pos %d\n", filename.c_str(), data_pos);
      data_pos = 138;
    }
    ASSERT(img_size == width * height * bpp);

    data = new unsigned char[img_size];
    unsigned char *row = new unsigned char[width * bpp];
    for(size_t y = 0; y < height; ++y) {
      r = fread(row, sizeof(unsigned char), width*bpp, file);
      ASSERT(r == width  * bpp);
      /* #pragma omp parallel for num_threads(4) */
      for(size_t x = 0; x < width; ++x) {
        unsigned char
          *dptr = &data[width * y * bpp + x * bpp],
          *rptr = &row[x * bpp];
        dptr[0] = rptr[2];
        dptr[1] = rptr[1];
        dptr[2] = rptr[0];
      }
    }
    delete [] row;
    fl.drop();
    fclose(file);
  }
};
}