Bitmap.cpp

#include <vector>
#include <fstream>
#include <cstring>

struct Pixel { unsigned char r, g, b; };

void WriteBMP(const char* fname, Pixel* a_pixelData, int width, int height)
{
  int paddedsize = (width*height) * sizeof(Pixel);

  unsigned char bmpfileheader[14] = {'B','M', 0,0,0,0, 0,0, 0,0, 54,0,0,0};
  unsigned char bmpinfoheader[40] = {40,0,0,0, 0,0,0,0, 0,0,0,0, 1,0, 24,0};

  bmpfileheader[ 2] = (unsigned char)(paddedsize    );
  bmpfileheader[ 3] = (unsigned char)(paddedsize>> 8);
  bmpfileheader[ 4] = (unsigned char)(paddedsize>>16);
  bmpfileheader[ 5] = (unsigned char)(paddedsize>>24);

  bmpinfoheader[ 4] = (unsigned char)(width    );
  bmpinfoheader[ 5] = (unsigned char)(width>> 8);
  bmpinfoheader[ 6] = (unsigned char)(width>>16);
  bmpinfoheader[ 7] = (unsigned char)(width>>24);
  bmpinfoheader[ 8] = (unsigned char)(height    );
  bmpinfoheader[ 9] = (unsigned char)(height>> 8);
  bmpinfoheader[10] = (unsigned char)(height>>16);
  bmpinfoheader[11] = (unsigned char)(height>>24);

  std::ofstream out(fname, std::ios::out | std::ios::binary);
  out.write((const char*)bmpfileheader, 14);
  out.write((const char*)bmpinfoheader, 40);
  out.write((const char*)a_pixelData, paddedsize);
  out.flush();
  out.close();
}

void SaveBMP(const char* fname, const unsigned int* pixels, int w, int h)
{
  std::vector<Pixel> pixels2(w*h);

  for (size_t i = 0; i < pixels2.size(); i++)
  {
    Pixel px;
    px.r       = (pixels[i] & 0x00FF0000) >> 16;
    px.g       = (pixels[i] & 0x0000FF00) >> 8;
    px.b       = (pixels[i] & 0x000000FF);
    pixels2[i] = px;
  }

  WriteBMP(fname, &pixels2[0], w, h);
}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

std::vector<unsigned int> LoadBMP(const char* filename, int* pW, int* pH)
{
  FILE* f = fopen(filename, "rb");

  if(f == NULL)
  {
    (*pW) = 0;
    (*pH) = 0;
    return std::vector<unsigned int>();
  }

  unsigned char info[54];
  fread(info, sizeof(unsigned char), 54, f); // read the 54-byte header

  int width  = *(int*)&info[18];
  int height = *(int*)&info[22];

  int row_padded      = (width*3 + 3) & (~3);
  unsigned char* data = new unsigned char[row_padded];

  std::vector<unsigned int> res(width*height);

  for(int i = 0; i < height; i++)
  {
    fread(data, sizeof(unsigned char), row_padded, f);
    for(int j = 0; j < width; j++)
      res[i*width+j] = (uint32_t(data[j*3+0]) << 16) | (uint32_t(data[j*3+1]) << 8)  | (uint32_t(data[j*3+2]) << 0);
  }

  fclose(f);
  delete [] data;

  (*pW) = width;
  (*pH) = height;
  return res;
}