Completely re-engineered version of Loopy, courtesy of Lambros

Lambrou. Now capable of handling triangular and hexagonal grids as
well as square ones, and then a number of semiregular plane tilings
and duals of semiregular ones. In fact, most of the solver code
supports an _arbitrary_ planar graph (well, provided both the graph
and its dual have no self-edges), so it could easily be extended
further with only a little more effort.

[originally from svn r8162]

grid.h

@@ -0,0 +1,96 @@
+/*
+ * (c) Lambros Lambrou 2008
+ *
+ * Code for working with general grids, which can be any planar graph
+ * with faces, edges and vertices (dots).  Includes generators for a few
+ * types of grid, including square, hexagonal, triangular and others.
+ */
+
+#ifndef PUZZLES_GRID_H
+#define PUZZLES_GRID_H
+
+/* Useful macros */
+#ifndef SQ
+#  define SQ(x) ( (x) * (x) )
+#endif
+
+/* ----------------------------------------------------------------------
+ * Grid structures:
+ * A grid is made up of faces, edges and dots.  These structures hold
+ * the incidence relationships between these types.  For example, an
+ * edge always joins two dots, and is adjacent to two faces.
+ * The "grid_xxx **" members are lists of pointers which are dynamically
+ * allocated during grid generation.
+ * A pointer to a face/edge/dot will always point somewhere inside one of the
+ * three lists of the main "grid" structure: faces, edges, dots.
+ * Could have used integer offsets into these lists, but using actual
+ * pointers instead gives us type-safety.
+ */
+
+/* Need forward declarations */
+typedef struct grid_face grid_face;
+typedef struct grid_edge grid_edge;
+typedef struct grid_dot grid_dot;
+
+struct grid_face {
+  int order; /* Number of edges, also the number of dots */
+  grid_edge **edges; /* edges around this face */
+  grid_dot **dots; /* corners of this face */
+};
+struct grid_edge {
+  grid_dot *dot1, *dot2;
+  grid_face *face1, *face2; /* Use NULL for the infinite outside face */
+};
+struct grid_dot {
+  int order;
+  grid_edge **edges;
+  grid_face **faces; /* A NULL grid_face* means infinite outside face */
+
+  /* Position in some fairly arbitrary (Cartesian) coordinate system.
+   * Use large enough values such that we can get away with
+   * integer arithmetic, but small enough such that arithmetic
+   * won't overflow. */
+  int x, y;
+};
+typedef struct grid {
+  /* These are (dynamically allocated) arrays of all the
+   * faces, edges, dots that are in the grid. */
+  int num_faces; grid_face *faces;
+  int num_edges; grid_edge *edges;
+  int num_dots;  grid_dot *dots;
+
+  /* Should be a face roughly near the middle of the grid.
+   * Used to seed path-generation, and also for nearest-edge
+   * detection. */
+  grid_face *middle_face;
+
+  /* Cache the bounding-box of the grid, so the drawing-code can quickly
+   * figure out the proper scaling to draw onto a given area. */
+  int lowest_x, lowest_y, highest_x, highest_y;
+
+  /* A measure of tile size for this grid (in grid coordinates), to help
+   * the renderer decide how large to draw the grid.
+   * Roughly the size of a single tile - for example the side-length
+   * of a square cell. */
+  int tilesize;
+
+  /* We really don't want to copy this monstrosity!
+   * A grid is immutable once generated.
+   */
+  int refcount;
+} grid;
+
+grid *grid_new_square(int width, int height);
+grid *grid_new_honeycomb(int width, int height);
+grid *grid_new_triangular(int width, int height);
+grid *grid_new_snubsquare(int width, int height);
+grid *grid_new_cairo(int width, int height);
+grid *grid_new_greathexagonal(int width, int height);
+grid *grid_new_octagonal(int width, int height);
+grid *grid_new_kites(int width, int height);
+
+void grid_free(grid *g);
+
+grid_edge *grid_nearest_edge(grid *g, int x, int y);
+
+#endif /* PUZZLES_GRID_H */

loopy.R

@@ -1,10 +1,10 @@
 # -*- makefile -*-
 
-LOOPY    = loopy tree234 dsf
+LOOPY     = loopy tree234 dsf grid
 
-loopy    : [X] GTK COMMON LOOPY loopy-icon|no-icon
+loopy     : [X] GTK COMMON LOOPY loopy-icon|no-icon
 
-loopy    : [G] WINDOWS COMMON LOOPY loopy.res|noicon.res
+loopy     : [G] WINDOWS COMMON LOOPY loopy.res|noicon.res
 
 ALL += LOOPY
 

puzzles.but

@@ -1797,17 +1797,26 @@ Unreasonable puzzles may require guessing and backtracking.
 
 \cfg{winhelp-topic}{games.loopy}
 
-You are given a grid of dots. Your aim is to draw a single unbroken
+You are given a grid of dots, marked with yellow lines to indicate
+which dots you are allowed to connect directly together. Your aim is
+to use some subset of those yellow lines to draw a single unbroken
 loop from dot to dot within the grid.
 
-Some of the square spaces between the dots contain numbers. These
+Some of the spaces between the lines contain numbers. These numbers
-numbers indicate how many of the four edges of that square are part
+indicate how many of the lines around that space form part of the
-of the loop. The loop you draw must correctly satisfy all of these
+loop. The loop you draw must correctly satisfy all of these clues to
-clues to be considered a correct solution.
+be considered a correct solution.
 
-Credit for this puzzle goes to \i{Nikoli} \k{nikoli-loopy}.
+In the default mode, the dots are arranged in a grid of squares;
+however, you can also play on triangular or hexagonal grids, or even
+more exotic ones.
 
-Loopy was contributed to this collection by Mike Pinna.
+Credit for the basic puzzle idea goes to \i{Nikoli}
+\k{nikoli-loopy}.
+
+Loopy was originally contributed to this collection by Mike Pinna,
+and subsequently enhanced to handle various types of non-square grid
+by Lambros Lambrou.
 
 \B{nikoli-loopy}
 \W{http://www.nikoli.co.jp/puzzles/3/index-e.htm}\cw{http://www.nikoli.co.jp/puzzles/3/index-e.htm}
@@ -1817,12 +1826,14 @@ Loopy was contributed to this collection by Mike Pinna.
 
 \IM{Loopy controls} controls, for Loopy
 
-Click the left mouse button between two dots to add a line segment
+Click the left mouse button on a yellow line to turn it black,
-connecting them. Click again to remove that line segment.
+indicating that you think it is part of the loop. Click again to
+turn the line yellow again (meaning you aren't sure yet).
 
 If you are sure that a particular line segment is \e{not} part of
-the loop, you can click the right mouse button to add a small cross
+the loop, you can click the right mouse button to remove it
-indicating this. Click again to remove the cross.
+completely. Again, clicking a second time will turn the line back to
+yellow.
 
 (All the actions described in \k{common-actions} are also available.)
 
@@ -1833,7 +1844,20 @@ These parameters are available from the \q{Custom...} option on the
 
 \dt \e{Width}, \e{Height}
 
-\dd Size of grid in squares.
+\dd Size of grid, measured in number of regions across and down. For
+square grids, it's clear how this is counted; for other types of
+grid you may have to think a bit to see how the dimensions are
+measured.
+
+\dt \e{Grid type}
+
+\dd Allows you to choose between a selection of types of tiling.
+Some have all the faces the same but may have multiple different
+types of vertex (e.g. the \e{Cairo} or \e{Kites} mode); others have
+all the vertices the same but may have differnt types of face (e.g.
+the \e{Great Hexagonal}). The square, triangular and honeycomb grids
+are fully regular, and have all their vertices \e{and} faces the
+same; this makes them the least confusing to play.
 
 \dt \e{Difficulty}