X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ian/git?a=blobdiff_plain;f=primer.c;h=f023b10365881f25c3de3f4e7b9a23e3bc2c4586;hb=b462f455cbaa1d716ff6d7b83ae4e1092ba3092a;hp=eaa345939c93f8189ad889f5c1086ac04b8e7aef;hpb=f5fef8bc75d9d5658705763fa7c083ae75a501ba;p=moebius2.git

diff --git a/primer.c b/primer.c
index eaa3459..f023b10 100644
--- a/primer.c
+++ b/primer.c
@@ -8,20 +8,28 @@
 #include "mgraph.h"
 
 int main(int argc, const char **argv) {
-  int v, k;
+  static const int prec= DBL_DIG+2;
+  int vi, k;
   
   if (argc>1) { fputs("no args please\n",stderr); exit(8); }
 
   printf("print %d, %d, %d, %d, %d\n", DIM, N, X, Y, D3);
   
-  FOR_VERTEX(v) {
-    int x= v & XMASK; /* distance along strip */
-    int y= y >> YSHIFT; /* distance across strip */
-    double u= y * 1.0 / (Y-1);
-    double v= x * M_PI / (X-1); /* SGT's u runs 0..pi along the strip */
-    K printf("print %c(%.*g,%.*g)\n",
-	     "xyz"[k],
-	     DBL_DIG+2,u, DBL_DIG+2,v);
+  FOR_VERTEX(vi) {
+    int x= vi & XMASK; /* distance along strip */
+    int y= vi >> YSHIFT; /* distance across strip */
+    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).
+     * 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,
+	     vi, x, y);
   }
   flushoutput();
   return 0;