Inspects header of the image file and returns the width, height, depth and size in bytes Suppoted formats: dds, sgi rgb, jpg, png, tga, bmp

ReadImageAttr.cc

 /*
 Inspects header of the image file and returns the width, height, depth and size in bytes
 Suppoted formats: dds, sgi rgb, jpg, png, tga, bmp
 
 You have to provide the implementation for:
 * _swap16/32: Is a byte order swap for little endian platforms, because most of the formats are in network order (big endian).
 * ExtensionIs: Returns true if the filename has the passed extension
 
 Note: For the DDS format, if the depth is negative, then it specifies the compression format. -1 for DXT1, -2 for DXT2 and so on.
 Note: ImgAttr might be removed and passing width/height/depth/size as out parameters of the function.
 */

struct ImgAttr
{
  int width;
  int height;
  int depth;
  int size;
}; 

// (Hamming weight) returns number of bits that are set in an 32 bits int
int32_t CountBits(int32_t i);


// Inspects header of the image file and returns the width, height, depth and size in bytes
bool ReadImageAttr(const char* filename, ImgAttr* attr)
{
  attr->width=attr->height=0;
  attr->depth=attr->size=0;
  char c;
  unsigned short u16;
  FILE* f = fopen(filename,"rb");
  if ( !f ) return false;

  if ( ExtensionIs(filename,".rgb") || ExtensionIs(filename,".rgba") || ExtensionIs(filename,".sgi") )
  {
    fseek(f,6,SEEK_SET);    
    fread(&u16, 1, 2, f); _swap16(&u16); attr->width=u16;
    fread(&u16, 1, 2, f); _swap16(&u16); attr->height=u16;    
    fread(&u16, 1, 2, f); _swap16(&u16); attr->depth=u16<<3;
  }
  else if ( ExtensionIs(filename, ".dds") )
  {
    fseek(f,12,SEEK_SET);
    fread(&attr->height, 1, 4, f);
    fread(&attr->width, 1, 4, f);
    fseek(f,12+44+4,SEEK_CUR);
    unsigned int flags, fourcc, rgbbc, masks[4];
    fread(&flags,1,4,f);
    fread(&fourcc,1,4,f);
    fread(&rgbbc,1,4,f);
    fread(masks,4,4,f);
    if (flags & 0x4 )
    {
      const char* fcc=(const char*)&fourcc;
      attr->depth = -(fcc[3]-'1'+1);
    }
    else if ( (flags & 0x1) || (flags & 0x40) )
    {
      unsigned int allm=masks[0]|masks[1]|masks[2]|masks[3];
      attr->depth = CountBits(allm);
    }
  }
  else if ( ExtensionIs(filename, ".jpeg") || ExtensionIs(filename,".jpg") )
  {
    unsigned char tmp[2048];    
    int r = fread(tmp,1,2048,f);
    int i = 0;
    while ((i++)<r)
    {
      if ( tmp[i]!=0xff ) continue;
      ++i; if ( i>=r ) break;
      switch(tmp[i])
      {
      case 0xc0:
      case 0xc1:
      case 0xc2:        
        i+=4; if ( i>=r ) break;
        u16 = *(unsigned short*)(tmp+i);_swap16(&u16); attr->width=u16;i+=2;
        u16= *(unsigned short*)(tmp+i);_swap16(&u16); attr->height=u16;i+=2;
        attr->depth= ( *(unsigned char*)(tmp+i) ) << 3;
        i=r;
        break;
      }
    }
  }
  else if (ExtensionIs(filename, ".png") )
  {
    fseek(f, 16, SEEK_SET);
    fread(&attr->width, 1, 4, f); _swap32(&attr->width);
    fread(&attr->height, 1, 4, f); _swap32(&attr->height);
    fread(&c,1,1,f); attr->depth = c<<3;
  }
  else if (ExtensionIs(filename, ".tga"))
  {
    fseek(f,12,SEEK_SET);
    fread(&u16, 1, 2, f); attr->width=u16;
    fread(&u16, 1, 2, f); attr->height=u16;
    fread(&c,1,1,f); attr->depth = c;
  }
  else if (ExtensionIs(filename,".bmp"))
  {
    fseek(f,14,SEEK_SET);
    fread(&u16, 1, 2, f); attr->width=u16;
    fread(&u16, 1, 2, f); attr->height=u16;
    fseek(f,2,SEEK_CUR);
    fread(&u16, 1, 2, f); attr->depth=u16;
  }

  fseek(f,0,SEEK_END);
  attr->size = ftell(f);
  fclose(f);
  return true;
}

// Hamming weight
int32_t CountBits(int32_t i)
{
  i = i - ((i >> 1) & 0x55555555);
  i = (i & 0x33333333) + ((i >> 2) & 0x33333333);
  return (((i + (i >> 4)) & 0x0F0F0F0F) * 0x01010101) >> 24;
}