minor improvements

[moebius2.git] / mgraph.c

diff --git a/mgraph.c b/mgraph.c
index 222bd094a92be74d70a52a6b0b05606a2a0b337c..4b708e5bd12c247ca21e78e6a1d082217908702d 100644 (file)
--- a/mgraph.c
+++ b/mgraph.c
@@ -4,36 +4,35 @@
 
 #include "mgraph.h"
 
-static const unsigned dx[V6]= {   0,  +1,  -1,  +1,  -1,   0  },
-                      dy[V6]= { +Y1, +Y1,   0,   0, -Y1, -Y1  };
-
+static const unsigned dx[2][V6]= {{  +1,   0,  -1,  -1,  -1,   0  },
+                                 {  +1,  +1,   0,  -1,   0,  +1  }},
+                      dy[V6]=     {   0, -Y1, -Y1,   0, +Y1, +Y1  };
 
 int edge_end2(unsigned v1, int e) {
-  /* The topology is equivalent to that of a square lattice with only
-   * half of the diagonals.  Ie, the result of shearing the triangular
-   * lattice to make the lines of constant x vertical.  This gives
-   * these six directions:
-   *
-   *                0  1
-   *                | /
-   *                |/
-   *             2--*--3
-   *              /|
-   *             / |
-   *            4  5
-   *
-   * This also handily makes vertical the numbering discontinuity,
-   * where the join happens.
-   */
   unsigned x, y;
 
   y= (v1 & YMASK) + dy[e];
-  if (y & ~YMASK) return -1;
+  if (y >= Y*Y1) return -1;
 
-  x= (v1 & XMASK) + dx[e];
+  x= (v1 & XMASK) + dx[(v1 >> YSHIFT) & 1][e];
   if (x & ~XMASK) {
+    //int orgy= y;
     y= (Y-1)*Y1 - y;
     x &= XMASK;;
+    //printf("%40s %02x -%d-> %02x  (was %02x) \n", "", v1, e, x|y, x|orgy);
   }
+  
   return x | y;
 }
+
+static const unsigned reverse[2][V6]= {{ 3, 4, 5, 0, 1, 2 },
+                                      { 3, 2, 1, 0, 5, 4 }};
+
+int edge_reverse(int v1, int e) {
+  unsigned x2;
+  int flip;
+
+  x2= (v1 & XMASK) + dx[(v1 >> YSHIFT) & 1][e];
+  flip= !!(x2 & ~XMASK);
+  return reverse[flip][e];
+}