1 files changed, 67 insertions, 0 deletions

diff --git a/apps/plugins/puzzles/src/hat.h b/apps/plugins/puzzles/src/hat.h
new file mode 100644
index 0000000000..39e2d31a66
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+++ b/apps/plugins/puzzles/src/hat.h
@@ -0,0 +1,67 @@
+#ifndef PUZZLES_HAT_H
+#define PUZZLES_HAT_H
+
+struct HatPatchParams {
+    /*
+     * A patch of hat tiling is identified by giving the coordinates
+     * of the kite in one corner, using a multi-level coordinate
+     * system based on metatile expansions. Coordinates are a sequence
+     * of small non-negative integers. The valid range for each
+     * coordinate depends on the next coordinate, or on final_metatile
+     * if it's the last one in the list. The largest valid range is
+     * {0,...,12}.
+     *
+     * 'final_metatile' is one of the characters 'H', 'T', 'P' or 'F'.
+     */
+    size_t ncoords;
+    unsigned char *coords;
+    char final_metatile;
+};
+
+/*
+ * Fill in HatPatchParams with a randomly selected set of coordinates,
+ * in enough detail to generate a patch of tiling covering an area of
+ * w x h 'squares' of a kite tiling.
+ *
+ * The kites grid is considered to be oriented so that it includes
+ * horizontal lines and not vertical ones. So each of the smallest
+ * equilateral triangles in the grid has a bounding rectangle whose
+ * height is sqrt(3)/2 times its width, and either the top or the
+ * bottom of that bounding rectangle is the horizontal edge of the
+ * triangle. A 'square' of a kite tiling (for convenience of choosing
+ * grid dimensions) counts as one of those bounding rectangles.
+ *
+ * The 'coords' field of the structure will be filled in with a new
+ * dynamically allocated array. Any previous pointer in that field
+ * will be overwritten.
+ */
+void hat_tiling_randomise(struct HatPatchParams *params, int w, int h,
+                          random_state *rs);
+
+/*
+ * Validate a HatPatchParams to ensure it contains no illegal
+ * coordinates. Returns NULL if it's acceptable, or an error string if
+ * not.
+ */
+const char *hat_tiling_params_invalid(const struct HatPatchParams *params);
+
+/*
+ * Generate the actual set of hat tiles from a HatPatchParams, passing
+ * each one to a callback. The callback receives the vertices of each
+ * point, as a sequence of 2*nvertices integers, with x,y coordinates
+ * interleaved.
+ *
+ * The x coordinates are measured in units of 1/4 of the side length
+ * of the smallest equilateral triangle, or equivalently, 1/2 the
+ * length of one of the long edges of a single kite. The y coordinates
+ * are measured in units of 1/6 the height of the triangle, which is
+ * also 1/2 the length of the short edge of a kite. Therefore, you can
+ * expect x to go up to 4*w and y up to 6*h.
+ */
+typedef void (*hat_tile_callback_fn)(void *ctx, size_t nvertices,
+                                     int *coords);
+
+void hat_tiling_generate(const struct HatPatchParams *params, int w, int h,
+                         hat_tile_callback_fn cb, void *cbctx);
+
+#endif