Checkpoint work on spiral labels

tile.cpp

@@ -1800,6 +1800,84 @@ static bool line_is_too_small(drawvec const &geometry, int z, int detail) {
 	return true;
 }
 
+static double dist(long long x1, long long y1, long long x2, long long y2) {
+	double dx = x2 - x1;
+	double dy = y2 - y1;
+	return sqrt(dx * dx + dy * dy);
+}
+
+drawvec spiral_anchors(drawvec const &geom, int tx, int ty, int z, unsigned long long label_point) {
+	drawvec out;
+
+	// anchor point in world coordinates
+	unsigned wx, wy;
+	decode_index(label_point, &wx, &wy);
+	printf("point %u,%u\n", wx, wy);
+
+	// upper left of tile in world coordinates
+	long long tx1 = 0, ty1 = 0;
+	// lower right of tile in world coordinates;
+	long long tx2 = 1LL << 32, ty2 = 1LL << 32;
+	if (z != 0) {
+		tx1 = (long long) tx << (32 - z);
+		ty1 = (long long) ty << (32 - z);
+
+		tx2 = (long long) (tx + 1) << (32 - z);
+		ty2 = (long long) (ty + 1) << (32 - z);
+	}
+	printf("tile %lld,%lld to %lld,%lld\n", tx1, ty1, tx2, ty2);
+
+	// min and max distance of corners of this tile from the label point
+	double min_radius, max_radius;
+	if (wx >= tx1 && wx <= tx2 && wy >= ty1 && wy <= ty2) {
+		// center is in this tile
+		min_radius = 0;
+	} else {
+		// center is elsewhere
+		min_radius = std::min(dist(wx, wy, tx1, ty1),
+				      std::min(dist(wx, wy, tx2, ty1),
+					       std::min(dist(wx, wy, tx2, ty2),
+							dist(wx, wy, tx1, ty2))));
+	}
+
+	max_radius = std::max(dist(wx, wy, tx1, ty1),
+			      std::max(dist(wx, wy, tx2, ty1),
+				       std::max(dist(wx, wy, tx2, ty2),
+						dist(wx, wy, tx1, ty2))));
+
+	printf("radius (world) %f to %f\n", min_radius, max_radius);
+
+	// from world coordinates to tiles
+	min_radius /= 1LL << (32 - z);
+	max_radius /= 1LL << (32 - z);
+
+	printf("radius (tiles) %f to %f\n", min_radius, max_radius);
+
+	// labels complete a circle every 0.02 tiles of radius
+	const double spiral_dist = 0.02;
+
+	size_t min_i = pow(min_radius / spiral_dist, 2);
+	size_t max_i = pow(max_radius / spiral_dist, 2);
+
+	// https://craftofcoding.wordpress.com/tag/sunflower-spiral/
+	double angle = M_PI * (3.0 - sqrt(5.0));  // 137.5 in radians
+
+	printf("making points %zu to %zu\n", min_i, max_i);
+	for (size_t i = min_i; i <= max_i; i++) {
+		double r = sqrt(i) * spiral_dist;
+		double theta = i * angle;
+		// Convert polar to cartesian
+		long long x = r * cos(theta) * (1LL << (32 - z)) + wx;
+		long long y = r * sin(theta) * (1LL << (32 - z)) + wy;
+
+		if (x >= tx1 && x <= tx2 && y >= ty1 && y <= ty2) {
+			out.push_back(draw(VT_MOVETO, x - tx1, y - ty1));
+		}
+	}
+
+	return out;
+}
+
 long long write_tile(FILE *geoms, std::atomic<long long> *geompos_in, char *metabase, char *stringpool, int z, const unsigned tx, const unsigned ty, const int detail, int min_detail, sqlite3 *outdb, const char *outdir, int buffer, const char *fname, FILE **geomfile, int minzoom, int maxzoom, double todo, std::atomic<long long> *along, long long alongminus, double gamma, int child_shards, long long *meta_off, long long *pool_off, unsigned *initial_x, unsigned *initial_y, std::atomic<int> *running, double simplification, std::vector<std::map<std::string, layermap_entry>> *layermaps, std::vector<std::vector<std::string>> *layer_unmaps, size_t tiling_seg, size_t pass, size_t passes, unsigned long long mingap, long long minextent, double fraction, const char *prefilter, const char *postfilter, struct json_object *filter, write_tile_args *arg, atomic_strategy *strategy) {
 	double merge_fraction = 1;
 	double mingap_fraction = 1;
@@ -2085,27 +2163,8 @@ long long write_tile(FILE *geoms, std::atomic<long long> *geompos_in, char *meta
 			}
 
 			if (sf.t == VT_POLYGON && additional[A_GENERATE_POLYGON_LABEL_POINTS]) {
-				// Checkerboard which tiles labels are generated for this polygon in,
-				// so we don't end up with multiple labels right next to each other.
-				// There is a label in the tile that the polygon nominally belongs to,
-				// and in other tiles reachable diagonally from there, but not in
-				// the ones directly on either side.
-
-				unsigned wx, wy;
-				decode_index(sf.index, &wx, &wy);
-
-				unsigned poly_tx = 0, poly_ty = 0;
-				if (z != 0) {
-					poly_tx = wx >> (32 - z);
-					poly_ty = wy >> (32 - z);
-
-					if (((tx - poly_tx + ty - poly_ty) & 1) != 0) {
-						continue;
-					}
-				}
-
 				sf.t = VT_POINT;
-				sf.geometry = polygon_to_anchor(sf.geometry);
+				sf.geometry = spiral_anchors(sf.geometry, tx, ty, z, sf.label_point);
 			}
 
 			if (sf.geometry.size() > 0) {