comments etc. fixed up for new topology

[moebius2.git] / primer.c

diff --git a/primer.c b/primer.c
index 42c4019da42d425e3da33b1f672e04319d97bec4..f023b10365881f25c3de3f4e7b9a23e3bc2c4586 100644 (file)
--- a/primer.c
+++ b/primer.c
@@ -21,9 +21,11 @@ int main(int argc, const char **argv) {
     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). */
-    double v= x * M_PI / X;
-    
+     * 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",
             "+-+"[k], "xyz"[k],
             prec+5,prec,u, prec+5,prec,v,