double u= y * 1.0 / (Y-1); /* SGT's u runs 0..1 across the strip */
/* SGT's v runs 0..pi along the strip, where the join is at 0==pi.
- * So that corresponds to 0..X (since 0==X in our scheme). */
+ * So that corresponds to 0..X (since 0==X in our scheme).
+ * Vertices with odd y coordinate are halfway to the next x coordinate.
+ */
double v= (x*2 + (y&1)) * M_PI / (X*2);
K printf("print %c%c( %-*.*g, %-*.*g); # %03x %2d %2d\n",