#include<stdio.h>
#include<cv.h>

/* useful function for reading in ppm/pgm headers */
void getline(char *buf,FILE *fp)
  {  //read until end of line from fp
	  char *p=buf;
	  char c;
	  while ((c=fgetc(fp))!='\n')
	    {	   *p=c;
		    p++;
	    }
	  *p='\0';//terminate as string
  }



/* some useful variables */
     CvSize imagesize;
     int sizeX,sizeY;
     IplImage *ip; 
     unsigned char *rawptr;
    char tstring[1000],inchar;
    FILE *fp;
     char fname[100];
     int radius;
     CvPoint centre;
     int colour;



 int main(int argc,char **argv)
{
	int i;
	/* read in image */
     printf("name of input?\n");
     scanf("%s",fname);
    fp = fopen(fname, "rb");
    if (!fp)
    {
	fprintf(stderr, "Unable to open file `%s'\n", fname);
	exit(1);
    }
    getline(tstring,fp);
    fprintf(stderr,"scanned %s\n",tstring);
    if (! ((tstring[0]=='P') && (tstring[1]=='5')) )
        { 
         fprintf(stderr,"can only work with P5 versions of ppm images\n");
         exit(-1);
          }
         /*Check for comment and swallow whole line */
    getline(tstring,fp);
    while (tstring[0]=='#') getline(tstring,fp); //skip comments
    if (sscanf(tstring, "%d %d", &sizeX, &sizeY) != 2)
    {
	fprintf(stderr, "Error loading image `%s'\n", fname);
	exit(1);
    }
    getline(tstring,fp);
    while (tstring[0]=='#') getline(tstring,fp); //skip comments
     // throw away the maxval

    imagesize.width=sizeX; imagesize.height=sizeY;
     ip= cvCreateImage(imagesize,IPL_DEPTH_8U,1);// 3 channels RGB
                                                  //default is 4 bytes align
     /* read image in one line at a time */
     rawptr= (unsigned char *) ip->imageData;
     for (i=0;i<sizeY;i++)
       {
       fread(rawptr,sizeX,1,fp);
       rawptr+= ip->widthStep; //increment padded line
       }
    fclose(fp);
    printf("successfully read in %d wide %d high image\n",ip->width,ip->height);

    /* process image */
     /* make up white colour */
     colour = 255;
     /* fix centre */
     printf("x coord of centre \n");
     scanf("%d",&centre.x);
     /*should check is inside image!! */
     printf("y coord of centre \n");
     scanf("%d",&centre.y);
     /*should check is inside image!! */
     printf("radius \n");
     scanf("%d",&radius);
     cvCircle(ip,centre,radius,colour,0); //0 for unfilled
    /* output image */
     printf("name of output?\n");
     scanf("%s",fname);
    fp = fopen(fname, "wb");
    fprintf(fp,"P5\n%d %d\n255\n",ip->width,ip->height);
     /* write image in out line at a time */
     rawptr= (unsigned char *) ip->imageData;
     for (i=0;i<sizeY;i++)
       {
       fwrite(rawptr,sizeX,1,fp);
       rawptr+= ip->widthStep; //increment padded line
       }
    fclose(fp);

    }