In direction :
    for(j=2; j<m1; j++){
        for(i=2; i<n1; i++){

look best from cells in quadrant :
            int n2 = i-3, m2 = j-3;
            for(int i1=i; i1>n2; --i1){
                for(int j1=j; j1>m2; --j1){
...
b[i][j] = best;
and repeat 4 times for all 4 directins and corresponding quadrant.
print answer :
    for(i=2; i<n1; i++){
        int sh=0;
        for(j=2; j<m1; j++){
            P p=P(i,j);
            int d = p.dist(b[i][j]);
            sh += sprintf(ans+sh,"%d ", d);
//            printf("%d ", d);
        }
        puts(ans);