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puzzles/hat.c
Simon Tatham 6fb890e0ea Reference my just-published article about aperiodic tilings. 
In commit 8d6647548f7d005 I added the Hats grid type to Loopy, and
mentioned in the commit message that I was very pleased with the
algorithm I came up with.

In fact, I was so pleased with it that I've decided it deserves a
proper public writeup. So I've spent the Easter weekend producing one:

  https://www.chiark.greenend.org.uk/~sgtatham/quasiblog/aperiodic-tilings/

In this commit I adjust the header comments in both penrose.c and
hat.c to refer to the article (replacing a previous comment in
penrose.c to a much less polished page containing a copy of my
jotting-grade personal notes that I sent James Harvey once). Also,
added some code to hatgen.c to output Python hat descriptions in a
similar style to hat-test, which I used to generate a couple of the
more difficult diagrams in the new article, and didn't want to lose.
2023-04-10 14:59:05 +01:00

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/*
* Code to generate patches of the aperiodic 'hat' tiling discovered
* in 2023.
*
* This uses the 'combinatorial coordinates' system documented in my
* public article
* https://www.chiark.greenend.org.uk/~sgtatham/quasiblog/aperiodic-tilings/
*
* The internal document auxiliary/doc/hats.html also contains an
* explanation of the basic ideas of this algorithm (less polished but
* containing more detail).
*
* Neither of those documents can really be put in a source file,
* because they just have too many complicated diagrams. So read at
* least one of those first; the comments in here will refer to it.
*
* Discoverers' website: https://cs.uwaterloo.ca/~csk/hat/
* Preprint of paper: https://arxiv.org/abs/2303.10798
*/
#include <assert.h>
#ifdef NO_TGMATH_H
# include <math.h>
#else
# include <tgmath.h>
#endif
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "puzzles.h"
#include "hat.h"
#include "hat-internal.h"
void hat_kiteenum_first(KiteEnum *s, int w, int h)
{
Kite start = { {0,0}, {0, 3}, {3, 0}, {2, 2} };
size_t i;
for (i = 0; i < KE_NKEEP; i++)
s->recent[i] = start; /* initialise to *something* */
s->curr_index = 0;
s->curr = &s->recent[s->curr_index];
s->state = 1;
s->w = w;
s->h = h;
s->x = 0;
s->y = 0;
}
bool hat_kiteenum_next(KiteEnum *s)
{
unsigned lastbut1 = s->last_index;
s->last_index = s->curr_index;
s->curr_index = (s->curr_index + 1) % KE_NKEEP;
s->curr = &s->recent[s->curr_index];
switch (s->state) {
/* States 1,2,3 walk rightwards along the upper side of a
* horizontal grid line with a pointy kite end at the start
* point */
case 1:
s->last_step = KS_F_RIGHT;
s->state = 2;
break;
case 2:
if (s->x+1 >= s->w) {
s->last_step = KS_F_RIGHT;
s->state = 4;
break;
}
s->last_step = KS_RIGHT;
s->state = 3;
s->x++;
break;
case 3:
s->last_step = KS_RIGHT;
s->state = 1;
break;
/* State 4 is special: we've just moved up into a row below a
* grid line, but we can't produce the rightmost tile of that
* row because it's not adjacent any tile so far emitted. So
* instead, emit the second-rightmost tile, and next time,
* we'll emit the rightmost. */
case 4:
s->last_step = KS_LEFT;
s->state = 5;
break;
/* And now we have to emit the third-rightmost tile relative
* to the last but one tile we emitted (the one from state 2,
* not state 4). */
case 5:
s->last_step = KS_RIGHT;
s->last_index = lastbut1;
s->state = 6;
break;
/* Now states 6-8 handle the general case of walking leftwards
* along the lower side of a line, starting from a
* right-angled kite end. */
case 6:
if (s->x <= 0) {
if (s->y+1 >= s->h) {
s->state = 0;
return false;
}
s->last_step = KS_RIGHT;
s->state = 9;
s->y++;
break;
}
s->last_step = KS_F_RIGHT;
s->state = 7;
s->x--;
break;
case 7:
s->last_step = KS_RIGHT;
s->state = 8;
break;
case 8:
s->last_step = KS_RIGHT;
s->state = 6;
break;
/* States 9,10,11 walk rightwards along the upper side of a
* horizontal grid line with a right-angled kite end at the
* start point. This time there's no awkward transition from
* the previous row. */
case 9:
s->last_step = KS_RIGHT;
s->state = 10;
break;
case 10:
s->last_step = KS_RIGHT;
s->state = 11;
break;
case 11:
if (s->x+1 >= s->w) {
/* Another awkward transition to the next row, where we
* have to generate it based on the previous state-9 tile.
* But this time at least we generate the rightmost tile
* of the new row, so the next states will be simple. */
s->last_step = KS_F_RIGHT;
s->last_index = lastbut1;
s->state = 12;
break;
}
s->last_step = KS_F_RIGHT;
s->state = 9;
s->x++;
break;
/* States 12,13,14 walk leftwards along the upper edge of a
* horizontal grid line with a pointy kite end at the start
* point */
case 12:
s->last_step = KS_F_RIGHT;
s->state = 13;
break;
case 13:
if (s->x <= 0) {
if (s->y+1 >= s->h) {
s->state = 0;
return false;
}
s->last_step = KS_LEFT;
s->state = 1;
s->y++;
break;
}
s->last_step = KS_RIGHT;
s->state = 14;
s->x--;
break;
case 14:
s->last_step = KS_RIGHT;
s->state = 12;
break;
default:
return false;
}
*s->curr = kite_step(s->recent[s->last_index], s->last_step);
return true;
}
/*
* The actual tables.
*/
#include "hat-tables.h"
/*
* One set of tables that we write by hand: the permitted ways to
* extend the coordinate system outwards from a given metatile.
*
* One obvious approach would be to make a table of all the places
* each metatile can appear in the expansion of another (e.g. H can be
* subtile 0, 1 or 2 of another H, subtile 0 of a T, or 0 or 1 of a P
* or an F), and when we need to decide what our current topmost tile
* turns out to be a subtile of, choose equiprobably at random from
* those options.
*
* That's what I did originally, but a better approach is to skew the
* probabilities. We'd like to generate our patch of actual tiling
* uniformly at random, in the sense that if you selected uniformly
* from a very large region of the plane, the distribution of possible
* finite patches of tiling would converge to some limit as that
* region tended to infinity, and we'd be picking from that limiting
* distribution on finite patches.
*
* For this we have to refer back to the original paper, which
* indicates the subset of each metatile's expansion that can be
* considered to 'belong' to that metatile, such that every subtile
* belongs to exactly one parent metatile, and the overlaps are
* eliminated. Reading out the diagrams from their Figure 2.8:
*
* - H: we discard three of the outer F subtiles, in the symmetric
* positions index by our coordinates as 7, 10, 11. So we keep the
* remaining subtiles {0,1,2,3,4,5,6,8,9,12}, which consist of
* three H, one T, three P and three F.
*
* - T: only the central H expanded from a T is considered to belong
* to it, so we just keep {0}, a single H.
*
* - P: we discard everything intersected by a long edge of the
* parallelogram, leaving the central three tiles and the endmost
* pair of F. That is, we keep {0,1,4,5,10}, consisting of two H,
* one P and two F.
*
* - F: looks like P at one end, and we retain the corresponding set
* of tiles there, but at the other end we keep the two F on either
* side of the endmost one. So we keep {0,1,3,6,8,10}, consisting of
* two H, one P and _three_ F.
*
* Adding up the tile numbers gives us this matrix system:
*
* (H_1) (3 1 2 2)(H_0)
* (T_1) = (1 0 0 0)(T_0)
* (P_1) (3 0 1 1)(P_0)
* (F_1) (3 0 2 3)(F_0)
*
* which says that if you have a patch of metatiling consisting of H_0
* H tiles, T_0 T tiles etc, then this matrix shows the number H_1 of
* smaller H tiles, etc, expanded from it.
*
* If you expand _many_ times, that's equivalent to raising the matrix
* to a power:
*
* n
* (H_n) (3 1 2 2) (H_0)
* (T_n) = (1 0 0 0) (T_0)
* (P_n) (3 0 1 1) (P_0)
* (F_n) (3 0 2 3) (F_0)
*
* The limiting distribution of metatiles is obtained by looking at
* the four-way ratio between H_n, T_n, P_n and F_n as n tends to
* infinity. To calculate this, we find the eigenvalues and
* eigenvectors of the matrix, and extract the eigenvector
* corresponding to the eigenvalue of largest magnitude. (Things get
* more complicated in cases where there isn't a _unique_ eigenvalue
* of largest magnitude, but here, there is.)
*
* That eigenvector is
*
* [ 1 ] [ 1 ]
* [ (7 - 3 sqrt(5)) / 2 ] ~= [ 0.14589803375031545538 ]
* [ 3 sqrt(5) - 6 ] [ 0.70820393249936908922 ]
* [ (9 - 3 sqrt(5)) / 2 ] [ 1.14589803375031545538 ]
*
* So those are the limiting relative proportions of metatiles.
*
* So if we have a particular metatile, how likely is it for its
* parent to be one of those? We have to adjust by the number of
* metatiles of each type that each tile has as its children. For
* example, the P and F tiles have one P child each, but the H has
* three P children. So if we have a P, the proportion of H in its
* potential ancestry is three times what's shown here. (And T can't
* occur at all as a parent.)
*
* In other words, we should choose _each coordinate_ with probability
* corresponding to one of those numbers (scaled down so they all sum
* to 1). Continuing to use P as an example, it will be:
*
* - child 4 of H with relative probability 1
* - child 5 of H with relative probability 1
* - child 6 of H with relative probability 1
* - child 4 of P with relative probability 0.70820393249936908922
* - child 3 of F with relative probability 1.14589803375031545538
*
* and then we obtain the true probabilities by scaling those values
* down so that they sum to 1.
*
* The tables below give a reasonable approximation in 32-bit
* integers to these proportions.
*/
typedef struct MetatilePossibleParent {
TileType type;
unsigned index;
unsigned long probability;
} MetatilePossibleParent;
/* The above probabilities scaled up by 10000000 */
#define PROB_H 10000000
#define PROB_T 1458980
#define PROB_P 7082039
#define PROB_F 11458980
static const MetatilePossibleParent parents_H[] = {
{ TT_H, 0, PROB_H },
{ TT_H, 1, PROB_H },
{ TT_H, 2, PROB_H },
{ TT_T, 0, PROB_T },
{ TT_P, 0, PROB_P },
{ TT_P, 1, PROB_P },
{ TT_F, 0, PROB_F },
{ TT_F, 1, PROB_F },
};
static const MetatilePossibleParent parents_T[] = {
{ TT_H, 3, PROB_H },
};
static const MetatilePossibleParent parents_P[] = {
{ TT_H, 4, PROB_H },
{ TT_H, 5, PROB_H },
{ TT_H, 6, PROB_H },
{ TT_P, 4, PROB_P },
{ TT_F, 3, PROB_F },
};
static const MetatilePossibleParent parents_F[] = {
{ TT_H, 8, PROB_H },
{ TT_H, 9, PROB_H },
{ TT_H, 12, PROB_H },
{ TT_P, 5, PROB_P },
{ TT_P, 10, PROB_P },
{ TT_F, 6, PROB_F },
{ TT_F, 8, PROB_F },
{ TT_F, 10, PROB_F },
};
static const MetatilePossibleParent *const possible_parents[] = {
parents_H, parents_T, parents_P, parents_F,
};
static const size_t n_possible_parents[] = {
lenof(parents_H), lenof(parents_T), lenof(parents_P), lenof(parents_F),
};
/*
* Similarly, we also want to choose our absolute starting hat with
* close to uniform probability, which again we do by looking at the
* limiting ratio of the metatile types, and this time, scaling by the
* number of hats in each metatile.
*
* We cheatingly use the same MetatilePossibleParent struct, because
* it's got all the right fields, even if it has an inappropriate
* name.
*/
static const MetatilePossibleParent starting_hats[] = {
{ TT_H, 0, PROB_H },
{ TT_H, 1, PROB_H },
{ TT_H, 2, PROB_H },
{ TT_H, 3, PROB_H },
{ TT_T, 0, PROB_P },
{ TT_P, 0, PROB_P },
{ TT_P, 1, PROB_P },
{ TT_F, 0, PROB_F },
{ TT_F, 1, PROB_F },
};
#undef PROB_H
#undef PROB_T
#undef PROB_P
#undef PROB_F
HatCoords *hat_coords_new(void)
{
HatCoords *hc = snew(HatCoords);
hc->nc = hc->csize = 0;
hc->c = NULL;
return hc;
}
void hat_coords_free(HatCoords *hc)
{
if (hc) {
sfree(hc->c);
sfree(hc);
}
}
void hat_coords_make_space(HatCoords *hc, size_t size)
{
if (hc->csize < size) {
hc->csize = hc->csize * 5 / 4 + 16;
if (hc->csize < size)
hc->csize = size;
hc->c = sresize(hc->c, hc->csize, HatCoord);
}
}
HatCoords *hat_coords_copy(HatCoords *hc_in)
{
HatCoords *hc_out = hat_coords_new();
hat_coords_make_space(hc_out, hc_in->nc);
memcpy(hc_out->c, hc_in->c, hc_in->nc * sizeof(*hc_out->c));
hc_out->nc = hc_in->nc;
return hc_out;
}
static const MetatilePossibleParent *choose_mpp(
random_state *rs, const MetatilePossibleParent *parents, size_t nparents)
{
/*
* If we needed to do this _efficiently_, we'd rewrite all those
* tables above as cumulative frequency tables and use binary
* search. But this happens about log n times in a grid of area n,
* so it hardly matters, and it's easier to keep the tables
* legible.
*/
unsigned long limit = 0, value;
size_t i;
for (i = 0; i < nparents; i++)
limit += parents[i].probability;
value = random_upto(rs, limit);
for (i = 0; i+1 < nparents; i++) {
if (value < parents[i].probability)
return &parents[i];
value -= parents[i].probability;
}
assert(i == nparents - 1);
assert(value < parents[i].probability);
return &parents[i];
}
void hatctx_init_random(HatContext *ctx, random_state *rs)
{
const MetatilePossibleParent *starting_hat = choose_mpp(
rs, starting_hats, lenof(starting_hats));
ctx->rs = rs;
ctx->prototype = hat_coords_new();
hat_coords_make_space(ctx->prototype, 3);
ctx->prototype->c[2].type = starting_hat->type;
ctx->prototype->c[2].index = -1;
ctx->prototype->c[1].type = TT_HAT;
ctx->prototype->c[1].index = starting_hat->index;
ctx->prototype->c[0].type = TT_KITE;
ctx->prototype->c[0].index = random_upto(rs, HAT_KITES);
ctx->prototype->nc = 3;
}
static inline int metatile_char_to_enum(char metatile)
{
return (metatile == 'H' ? TT_H :
metatile == 'T' ? TT_T :
metatile == 'P' ? TT_P :
metatile == 'F' ? TT_F : -1);
}
static void init_coords_params(HatContext *ctx,
const struct HatPatchParams *hp)
{
size_t i;
ctx->rs = NULL;
ctx->prototype = hat_coords_new();
assert(hp->ncoords >= 3);
hat_coords_make_space(ctx->prototype, hp->ncoords + 1);
ctx->prototype->nc = hp->ncoords + 1;
for (i = 0; i < hp->ncoords; i++)
ctx->prototype->c[i].index = hp->coords[i];
ctx->prototype->c[hp->ncoords].type =
metatile_char_to_enum(hp->final_metatile);
ctx->prototype->c[hp->ncoords].index = -1;
ctx->prototype->c[0].type = TT_KITE;
ctx->prototype->c[1].type = TT_HAT;
for (i = hp->ncoords - 1; i > 1; i--) {
TileType metatile = ctx->prototype->c[i+1].type;
assert(hp->coords[i] < nchildren[metatile]);
ctx->prototype->c[i].type = children[metatile][hp->coords[i]];
}
assert(hp->coords[0] < 8);
}
HatCoords *hatctx_initial_coords(HatContext *ctx)
{
return hat_coords_copy(ctx->prototype);
}
/*
* Extend hc until it has at least n coordinates in, by copying from
* ctx->prototype if needed, and extending ctx->prototype if needed in
* order to do that.
*/
void hatctx_extend_coords(HatContext *ctx, HatCoords *hc, size_t n)
{
if (ctx->prototype->nc < n) {
hat_coords_make_space(ctx->prototype, n);
while (ctx->prototype->nc < n) {
TileType type = ctx->prototype->c[ctx->prototype->nc - 1].type;
assert(ctx->prototype->c[ctx->prototype->nc - 1].index == -1);
const MetatilePossibleParent *parent;
if (ctx->rs)
parent = choose_mpp(ctx->rs, possible_parents[type],
n_possible_parents[type]);
else
parent = possible_parents[type];
ctx->prototype->c[ctx->prototype->nc - 1].index = parent->index;
ctx->prototype->c[ctx->prototype->nc].index = -1;
ctx->prototype->c[ctx->prototype->nc].type = parent->type;
ctx->prototype->nc++;
}
}
hat_coords_make_space(hc, n);
while (hc->nc < n) {
assert(hc->c[hc->nc - 1].index == -1);
assert(hc->c[hc->nc - 1].type == ctx->prototype->c[hc->nc - 1].type);
hc->c[hc->nc - 1].index = ctx->prototype->c[hc->nc - 1].index;
hc->c[hc->nc].index = -1;
hc->c[hc->nc].type = ctx->prototype->c[hc->nc].type;
hc->nc++;
}
}
void hatctx_cleanup(HatContext *ctx)
{
hat_coords_free(ctx->prototype);
}
/*
* The actual system for finding the coordinates of an adjacent kite.
*/
/*
* Kitemap step: ensure we have enough coordinates to know two levels
* of meta-tiling, and use the kite map for the outer layer to move
* around the individual kites. If this fails, return NULL.
*/
static HatCoords *try_step_coords_kitemap(
HatContext *ctx, HatCoords *hc_in, KiteStep step)
{
hatctx_extend_coords(ctx, hc_in, 4);
hat_coords_debug(" try kitemap ", hc_in, "\n");
unsigned kite = hc_in->c[0].index;
unsigned hat = hc_in->c[1].index;
unsigned meta = hc_in->c[2].index;
TileType meta2type = hc_in->c[3].type;
const KitemapEntry *ke = &kitemap[meta2type][
kitemap_index(step, kite, hat, meta)];
if (ke->kite >= 0) {
/*
* Success! We've got coordinates for the next kite in this
* direction.
*/
HatCoords *hc_out = hat_coords_copy(hc_in);
hc_out->c[2].index = ke->meta;
hc_out->c[2].type = children[meta2type][ke->meta];
hc_out->c[1].index = ke->hat;
hc_out->c[1].type = TT_HAT;
hc_out->c[0].index = ke->kite;
hc_out->c[0].type = TT_KITE;
hat_coords_debug(" success! ", hc_out, "\n");
return hc_out;
}
return NULL;
}
/*
* Recursive metamap step. Try using the metamap to rewrite the
* coordinates at hc->c[depth] and hc->c[depth+1] (using the metamap
* for the tile type described in hc->c[depth+2]). If successful,
* recurse back down to see if this led to a successful step via the
* kitemap. If even that fails (so that we need to try a higher-order
* metamap rewrite), return NULL.
*/
static HatCoords *try_step_coords_metamap(
HatContext *ctx, HatCoords *hc_in, KiteStep step, size_t depth)
{
HatCoords *hc_tmp = NULL, *hc_out;
hatctx_extend_coords(ctx, hc_in, depth+3);
#ifdef HAT_COORDS_DEBUG
fprintf(stderr, " try meta %-4d", (int)depth);
hat_coords_debug("", hc_in, "\n");
#endif
unsigned meta_orig = hc_in->c[depth].index;
unsigned meta2_orig = hc_in->c[depth+1].index;
TileType meta3type = hc_in->c[depth+2].type;
unsigned meta = meta_orig, meta2 = meta2_orig;
while (true) {
const MetamapEntry *me;
HatCoords *hc_curr = hc_tmp ? hc_tmp : hc_in;
if (depth > 2)
hc_out = try_step_coords_metamap(ctx, hc_curr, step, depth - 1);
else
hc_out = try_step_coords_kitemap(ctx, hc_curr, step);
if (hc_out) {
hat_coords_free(hc_tmp);
return hc_out;
}
me = &metamap[meta3type][metamap_index(meta, meta2)];
assert(me->meta != -1);
if (me->meta == meta_orig && me->meta2 == meta2_orig) {
hat_coords_free(hc_tmp);
return NULL;
}
meta = me->meta;
meta2 = me->meta2;
/*
* We must do the rewrite in a copy of hc_in. It's not
* _necessarily_ obvious that that's the case (any successful
* rewrite leaves the coordinates still valid and still
* referring to the same kite, right?). But the problem is
* that we might do a rewrite at this level more than once,
* and in between, a metamap rewrite at the next level down
* might have modified _one_ of the two coordinates we're
* messing about with. So it's easiest to let the recursion
* just use a separate copy.
*/
if (!hc_tmp)
hc_tmp = hat_coords_copy(hc_in);
hc_tmp->c[depth+1].index = meta2;
hc_tmp->c[depth+1].type = children[meta3type][meta2];
hc_tmp->c[depth].index = meta;
hc_tmp->c[depth].type = children[hc_tmp->c[depth+1].type][meta];
hat_coords_debug(" rewritten -> ", hc_tmp, "\n");
}
}
/*
* The top-level algorithm for finding the next tile.
*/
HatCoords *hatctx_step(HatContext *ctx, HatCoords *hc_in, KiteStep step)
{
HatCoords *hc_out;
size_t depth;
#ifdef HAT_COORDS_DEBUG
static const char *const directions[] = {
" left\n", " right\n", " forward left\n", " forward right\n" };
hat_coords_debug("step start ", hc_in, directions[step]);
#endif
/*
* First, just try a kitemap step immediately. If that succeeds,
* we're done.
*/
if ((hc_out = try_step_coords_kitemap(ctx, hc_in, step)) != NULL)
return hc_out;
/*
* Otherwise, try metamap rewrites at successively higher layers
* until one works. Each one will recurse back down to the
* kitemap, as described above.
*/
for (depth = 2;; depth++) {
if ((hc_out = try_step_coords_metamap(
ctx, hc_in, step, depth)) != NULL)
return hc_out;
}
}
/*
* Generate a random set of parameters for a tiling of a given size.
* To do this, we iterate over the whole tiling via hat_kiteenum_first
* and hat_kiteenum_next, and for each kite, calculate its
* coordinates. But then we throw the coordinates away and don't do
* anything with them!
*
* But the side effect of _calculating_ all those coordinates is that
* we found out how far ctx->prototype needed to be extended, and did
* so, pulling random choices out of our random_state. So after this
* iteration, ctx->prototype contains everything we need to replicate
* the same piece of tiling next time.
*/
void hat_tiling_randomise(struct HatPatchParams *hp, int w, int h,
random_state *rs)
{
HatContext ctx[1];
HatCoords *coords[KE_NKEEP];
KiteEnum s[1];
size_t i;
hatctx_init_random(ctx, rs);
for (i = 0; i < lenof(coords); i++)
coords[i] = NULL;
hat_kiteenum_first(s, w, h);
coords[s->curr_index] = hatctx_initial_coords(ctx);
while (hat_kiteenum_next(s)) {
hat_coords_free(coords[s->curr_index]);
coords[s->curr_index] = hatctx_step(
ctx, coords[s->last_index], s->last_step);
}
hp->ncoords = ctx->prototype->nc - 1;
hp->coords = snewn(hp->ncoords, unsigned char);
for (i = 0; i < hp->ncoords; i++)
hp->coords[i] = ctx->prototype->c[i].index;
hp->final_metatile = tilechars[ctx->prototype->c[hp->ncoords].type];
hatctx_cleanup(ctx);
for (i = 0; i < lenof(coords); i++)
hat_coords_free(coords[i]);
}
const char *hat_tiling_params_invalid(const struct HatPatchParams *hp)
{
TileType metatile;
size_t i;
if (hp->ncoords < 3)
return "Grid parameters require at least three coordinates";
if (metatile_char_to_enum(hp->final_metatile) < 0)
return "Grid parameters contain an invalid final metatile";
if (hp->coords[0] >= 8)
return "Grid parameters contain an invalid kite index";
metatile = metatile_char_to_enum(hp->final_metatile);
for (i = hp->ncoords - 1; i > 1; i--) {
if (hp->coords[i] >= nchildren[metatile])
return "Grid parameters contain an invalid metatile index";
metatile = children[metatile][hp->coords[i]];
}
if (hp->coords[1] >= hats_in_metatile[metatile])
return "Grid parameters contain an invalid hat index";
return NULL;
}
void maybe_report_hat(int w, int h, Kite kite, HatCoords *hc,
internal_hat_callback_fn cb, void *cbctx)
{
Kite kite0;
Point vertices[14];
size_t i, j;
bool reversed = false;
int coords[28];
/* Only iterate from kite #0 of a hat */
if (hc->c[0].index != 0)
return;
kite0 = kite;
/*
* Identify reflected hats: they are always hat #3 of an H
* metatile. If we find one, reflect the starting kite so that the
* kite_step operations below will go in the other direction.
*/
if (hc->c[2].type == TT_H && hc->c[1].index == 3) {
reversed = true;
Point tmp = kite.left;
kite.left = kite.right;
kite.right = tmp;
}
vertices[0] = kite.centre;
vertices[1] = kite.right;
vertices[2] = kite.outer;
vertices[3] = kite.left;
kite = kite_left(kite); /* now on kite #1 */
kite = kite_forward_right(kite); /* now on kite #2 */
vertices[4] = kite.centre;
kite = kite_right(kite); /* now on kite #3 */
vertices[5] = kite.right;
vertices[6] = kite.outer;
kite = kite_forward_left(kite); /* now on kite #4 */
vertices[7] = kite.left;
vertices[8] = kite.centre;
kite = kite_right(kite); /* now on kite #5 */
kite = kite_right(kite); /* now on kite #6 */
kite = kite_right(kite); /* now on kite #7 */
vertices[9] = kite.right;
vertices[10] = kite.outer;
vertices[11] = kite.left;
kite = kite_left(kite); /* now on kite #6 again */
vertices[12] = kite.outer;
vertices[13] = kite.left;
if (reversed) {
/* For a reversed kite, also reverse the vertex order, so that
* we report every polygon in a consistent orientation */
for (i = 0, j = 13; i < j; i++, j--) {
Point tmp = vertices[i];
vertices[i] = vertices[j];
vertices[j] = tmp;
}
}
/*
* Convert from our internal coordinate system into the orthogonal
* one used in this module's external API. In the same loop, we
* might as well do the bounds check.
*/
for (i = 0; i < 14; i++) {
Point v = vertices[i];
int x = (v.x * 2 + v.y) / 3, y = v.y;
if (x < 0 || x > 4*w || y < 0 || y > 6*h)
return; /* a vertex of this kite is out of bounds */
coords[2*i] = x;
coords[2*i+1] = y;
}
cb(cbctx, kite0, hc, coords);
}
struct internal_ctx {
hat_tile_callback_fn external_cb;
void *external_cbctx;
};
static void report_hat(void *vctx, Kite kite0, HatCoords *hc, int *coords)
{
struct internal_ctx *ctx = (struct internal_ctx *)vctx;
ctx->external_cb(ctx->external_cbctx, 14, coords);
}
/*
* Generate a hat tiling from a previously generated set of parameters.
*/
void hat_tiling_generate(const struct HatPatchParams *hp, int w, int h,
hat_tile_callback_fn cb, void *cbctx)
{
HatContext ctx[1];
HatCoords *coords[KE_NKEEP];
KiteEnum s[1];
size_t i;
struct internal_ctx report_hat_ctx[1];
report_hat_ctx->external_cb = cb;
report_hat_ctx->external_cbctx = cbctx;
init_coords_params(ctx, hp);
for (i = 0; i < lenof(coords); i++)
coords[i] = NULL;
hat_kiteenum_first(s, w, h);
coords[s->curr_index] = hatctx_initial_coords(ctx);
maybe_report_hat(w, h, *s->curr, coords[s->curr_index],
report_hat, report_hat_ctx);
while (hat_kiteenum_next(s)) {
hat_coords_free(coords[s->curr_index]);
coords[s->curr_index] = hatctx_step(
ctx, coords[s->last_index], s->last_step);
maybe_report_hat(w, h, *s->curr, coords[s->curr_index],
report_hat, report_hat_ctx);
}
hatctx_cleanup(ctx);
for (i = 0; i < lenof(coords); i++)
hat_coords_free(coords[i]);
}
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