* -3 ___ X-2 ___ X-1 ___| 0 ___ 1 ___ 2 ___ 3 ___ 4 ___
* 0 0 0 |Y-1 Y-1 Y-1 Y-1 Y-1
* |
+ * ^ join, where there is
+ * a discontinuity in numbering
+ *
* Node x,y for
- * 0 <= x < X x = distance along
- * 0 <= y < Y y = distance across
+ * 0 <= x < X = 2^XBITS x = distance along
+ * 0 <= y < Y = 2^YBITS-1 y = distance across
*
* Vertices are in reading order from diagram above ie x varies fastest.
*
- * 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).
- *
* 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!
*
- * We label edges as follows: Or in the square view:
- *
- * \2 /1 2 1
- * \ / | /
- * ___ 0 __ |/
- * 3 1 0 3--*--0
- * / \ /|
- * 4/ 5\ / |
- * 4 5
+ * We label edges as follows:
*
- * (This makes the numbering
- * discontinuity, at the join,
- * vertical and thus tractable.)
+ * \2 /1
+ * \ /
+ * ___ 0 __
+ * 3 1 0
+ * / \
+ * 4/ 5\
*/
#ifndef MGRAPH_H
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",