tidyings, more points.

[moebius2.git] / mgraph.h

diff --git a/mgraph.h b/mgraph.h
index 3995d463ed0bda1160791fa997d2da40fde6ea66..08704894f7ab41841f11f44937a981f26c588a75 100644 (file)
--- a/mgraph.h
+++ b/mgraph.h
@@ -4,16 +4,16 @@
 /*
  * Vertices in strip are numbered as follows:
  *
- *     ___ X-2 ___ X-1 ___ 0   ___ 1   ___ 2   ___ 3   ___ 4   __
- *         Y-1     Y-1      0       0       0       0       0
+ *     ___ X-2 ___ X-1 ___  0  ___  1  ___  2  ___  3  ___  4  __
+ *         Y-1     Y-1     0       0       0       0       0 
  *        /  \    /  \    /  \    /  \    /  \    /  \    /  \
  *       /    \  /    \  /    \  /    \  /    \  /    \  /    \
- *     X-3 ___ X-2 ___ X-1 ___ 0   ___ 1   ___ 2   ___  3  ___ 4
- *     Y-2     Y-2     Y-2      1       1       1       1       1
+ *     X-3 ___ X-2 ___ X-1 ___  0  ___  1  ___  2  ___  3  ___  4
+ *     Y-2     Y-2     Y-2     1       1       1       1       1
  *       \    /  \    /  \    /  \    /  \    /  \    /  \    /
  *        \  /    \  /    \  /    \  /    \  /    \  /    \  /
- *     ___ X-3 ___ X-2 ___ X-1 ___ 0   ___ 1   ___ 2   ___ 3   __
- *         Y-3     Y-3     Y-3      2       2       2       2
+ *     ___ X-3 ___ X-2 ___ X-1 ___  0  ___  1  ___  2  ___  3  __
+ *         Y-3     Y-3     Y-3     2       2       2       2 
  *
  *       .   .   .   .   .   .   .   .   .   .   .   .   .   .   .
  *
@@ -33,14 +33,24 @@
  * Y must be even.  The actual location opposite (0,0) is (X-(Y-1)/2,0),
  * and likewise opposite (0,Y-1) is ((Y-1)/2,0).
  *
- * We label edges as follows:
+ * Note that though presentation above is equilateral triangles, this
+ * is not the case.  It's actually a square lattice with half of the
+ * diagonals added.  We can't straighten it out because at the join
+ * the diagonals point the other way!
  *
- *             e:          \2   /1
- *                          \  /
- *                       ___ 0   __
- *                       3    1   0
- *                          /  \
- *                        4/   5\
+ * We label edges as follows:        Or in the square view:
+ *
+ *                 \2   /1                 2  1  
+ *                  \  /                   | /   
+ *               ___ 0   __                |/    
+ *               3    1   0             3--*--0  
+ *                  /  \                  /|     
+ *                4/   5\                / |     
+ *                                      4  5
+ *
+ *                                   (This makes the numbering
+ *                                   discontinuity, at the join,
+ *                                   vertical and thus tractable.)
  */
 
 #ifndef MGRAPH_H
@@ -48,9 +58,11 @@
 
 #include "common.h"
 
-#define XBITS 4
+#define DIMBITS 5
+
+#define XBITS DIMBITS
 #define X (1<<XBITS)
-#define YBITS 4
+#define YBITS DIMBITS
 #define Y (1<<YBITS)
 
 /* vertex number:   0000 | y     | x