#include "stdio.h"
#include "stdlib.h"
#include "math.h"

/*
   Sample program to read a limited number of BMP file types
   Write out lots of diagnostics
   Write out a 24 bit RAW image file
*/

#define TRUE  1
#define FALSE 0

typedef struct {
   unsigned short int type;                 /* Magic identifier            */
   unsigned int size;                       /* File size in bytes          */
   unsigned short int reserved1, reserved2;
   unsigned int offset;                     /* Offset to image data, bytes */
} HEADER;
typedef struct {
   unsigned int size;               /* Header size in bytes      */
   int width,height;                /* Width and height of image */
   unsigned short int planes;       /* Number of colour planes   */
   unsigned short int bits;         /* Bits per pixel            */
   unsigned int compression;        /* Compression type          */
   unsigned int imagesize;          /* Image size in bytes       */
   int xresolution,yresolution;     /* Pixels per meter          */
   unsigned int ncolours;           /* Number of colours         */
   unsigned int importantcolours;   /* Important colours         */
} INFOHEADER;
typedef struct {
   unsigned char r,g,b,junk;
} COLOURINDEX;

int ReadUShort(FILE *,unsigned short *,int);
int ReadUInt(FILE *,unsigned int *,int);

int main(int argc,char **argv)
{
   int i,j;
   int gotindex = FALSE;
   unsigned char grey,r,g,b;
   HEADER header;
   INFOHEADER infoheader;
   COLOURINDEX colourindex[256];
   FILE *fptr;

   /* Check arguments */
   if (argc < 2) {
      fprintf(stderr,"Usage: %s filename\n",argv[0]);
      exit(-1);
   }

   /* Open file */
   if ((fptr = fopen(argv[1],"r")) == NULL) {
      fprintf(stderr,"Unable to open BMP file \"%s\"\n",argv[1]);
      exit(-1);
   }

   /* Read and check the header */
   ReadUShort(fptr,&header.type,FALSE);
   fprintf(stderr,"ID is: %d, should be %d\n",header.type,'M'*256+'B');
   ReadUInt(fptr,&header.size,FALSE);
   fprintf(stderr,"File size is %d bytes\n",header.size);
   ReadUShort(fptr,&header.reserved1,FALSE);
   ReadUShort(fptr,&header.reserved2,FALSE);
   ReadUInt(fptr,&header.offset,FALSE);
   fprintf(stderr,"Offset to image data is %d bytes\n",header.offset);

   /* Read and check the information header */
   if (fread(&infoheader,sizeof(INFOHEADER),1,fptr) != 1) {
      fprintf(stderr,"Failed to read BMP info header\n");
      exit(-1);
   }
   fprintf(stderr,"Image size = %d x %d\n",infoheader.width,infoheader.height);
   fprintf(stderr,"Number of colour planes is %d\n",infoheader.planes);
   fprintf(stderr,"Bits per pixel is %d\n",infoheader.bits);
   fprintf(stderr,"Compression type is %d\n",infoheader.compression);
   fprintf(stderr,"Number of colours is %d\n",infoheader.ncolours);
   fprintf(stderr,"Number of required colours is %d\n",
      infoheader.importantcolours);

   /* Read the lookup table if there is one */
   for (i=0;i<255;i++) {
      colourindex[i].r = rand() % 256;
      colourindex[i].g = rand() % 256;
      colourindex[i].b = rand() % 256;
      colourindex[i].junk = rand() % 256;
   }
   if (infoheader.ncolours > 0) {
      for (i=0;i<infoheader.ncolours;i++) {
         if (fread(&colourindex[i].b,sizeof(unsigned char),1,fptr) != 1) {
            fprintf(stderr,"Image read failed\n");
            exit(-1);
         }
         if (fread(&colourindex[i].g,sizeof(unsigned char),1,fptr) != 1) {
            fprintf(stderr,"Image read failed\n");
            exit(-1);
         }
         if (fread(&colourindex[i].r,sizeof(unsigned char),1,fptr) != 1) {
            fprintf(stderr,"Image read failed\n");
            exit(-1);
         }
         if (fread(&colourindex[i].junk,sizeof(unsigned char),1,fptr) != 1) {
            fprintf(stderr,"Image read failed\n");
            exit(-1);
         }
         fprintf(stderr,"%3d\t%3d\t%3d\t%3d\n",i,
            colourindex[i].r,colourindex[i].g,colourindex[i].b);
      }
      gotindex = TRUE;
   }

   /* Seek to the start of the image data */
   fseek(fptr,header.offset,SEEK_SET);

   /* Read the image */
   for (j=0;j<infoheader.height;j++) {
      for (i=0;i<infoheader.width;i++) {

         switch (infoheader.bits) {
         case 1:
            break;
         case 4:
            break;
         case 8:
            if (fread(&grey,sizeof(unsigned char),1,fptr) != 1) {
               fprintf(stderr,"Image read failed\n");
               exit(-1);
            }
            if (gotindex) {
               putchar(colourindex[grey].r);
               putchar(colourindex[grey].g);
               putchar(colourindex[grey].b);
            } else {
               putchar(grey);
            }
            break;
         case 24:
            if (fread(&b,sizeof(unsigned char),1,fptr) != 1) {
               fprintf(stderr,"Image read failed\n");
               exit(-1);
            }
            if (fread(&g,sizeof(unsigned char),1,fptr) != 1) {
               fprintf(stderr,"Image read failed\n");
               exit(-1);
            }
            if (fread(&r,sizeof(unsigned char),1,fptr) != 1) {
               fprintf(stderr,"Image read failed\n");
               exit(-1);
            }
            putchar(r);
            putchar(g);
            putchar(b);
            break;
         }

      } /* i */
   } /* j */

   fclose(fptr);
}

/*
   Read a possibly byte swapped unsigned short integer
*/
int ReadUShort(FILE *fptr,short unsigned *n,int swap)
{
   unsigned char *cptr,tmp;

   if (fread(n,2,1,fptr) != 1)
      return(FALSE);
   if (swap) {
      cptr = (unsigned char *)n;
      tmp = cptr[0];
      cptr[0] = cptr[1];
      cptr[1] =tmp;
   }
   return(TRUE);
}

/*
   Read a possibly byte swapped unsigned integer
*/
int ReadUInt(FILE *fptr,unsigned int *n,int swap)
{
   unsigned char *cptr,tmp;

   if (fread(n,4,1,fptr) != 1)
      return(FALSE);
   if (swap) {
      cptr = (unsigned char *)n;
      tmp = cptr[0];
      cptr[0] = cptr[3];
      cptr[3] = tmp;
      tmp = cptr[1];
      cptr[1] = cptr[2];
      cptr[2] = tmp;
   }
   return(TRUE);
}