Port of Simon Tatham's Puzzle Collection

Original revision: 5123b1bf68777ffa86e651f178046b26a87cf2d9

MIT Licensed. Some games still crash and others are unplayable due to
issues with controls. Still need a "real" polygon filling algorithm.

Currently builds one plugin per puzzle (about 40 in total, around 100K
each on ARM), but can easily be made to build a single monolithic
overlay (800K or so on ARM).

The following games are at least partially broken for various reasons,
and have been disabled on this commit:

Cube:     failed assertion with "Icosahedron" setting
Keen:     input issues
Mines:    weird stuff happens on target
Palisade: input issues
Solo:     input issues, occasional crash on target
Towers:   input issues
Undead:   input issues
Unequal:  input and drawing issues (concave polys)
Untangle: input issues

Features left to do:
 - In-game help system
 - Figure out the weird bugs

Change-Id: I7c69b6860ab115f973c8d76799502e9bb3d52368

apps/plugins/puzzles/loopgen.h

@@ -0,0 +1,35 @@
+/*
+ * loopgen.h: interface file for loop generation functions for grid.[ch].
+ */
+
+#ifndef _LOOPGEN_H
+#define _LOOPGEN_H
+
+#include "puzzles.h"
+#include "grid.h"
+
+enum face_colour { FACE_WHITE, FACE_GREY, FACE_BLACK };
+
+/* face should be of type grid_face* here. */
+#define FACE_COLOUR(face) \
+    ( (face) == NULL ? FACE_BLACK : \
+	  board[(face) - g->faces] )
+
+typedef int (*loopgen_bias_fn_t)(void *ctx, char *board, int face);
+
+/* 'board' should be a char array whose length is the same as
+ * g->num_faces: this will be filled in with FACE_WHITE or FACE_BLACK
+ * after loop generation.
+ *
+ * If 'bias' is non-null, it should be a user-provided function which
+ * rates a half-finished board (i.e. may include some FACE_GREYs) for
+ * desirability; this will cause the loop generator to bias in favour
+ * of loops with a high return value from that function. The 'face'
+ * parameter to the bias function indicates which face of the grid has
+ * been modified since the last call; it is guaranteed that only one
+ * will have been (so that bias functions can work incrementally
+ * rather than re-scanning the whole grid on every call). */
+extern void generate_loop(grid *g, char *board, random_state *rs,
+                          loopgen_bias_fn_t bias, void *biasctx);
+
+#endif