Prescan for small deltas before doing proper simplification

clip.cpp

@@ -789,14 +789,14 @@ double distance_from_line(long long point_x, long long point_y, long long segA_x
 void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, size_t retain, bool prevent_simplify_shared_nodes) {
 	std::stack<int> recursion_stack;
 
-	if (!geom[start + 0].necessary || !geom[start + n - 1].necessary) {
+	if (!(geom[start + 0].necessary > 0) || !(geom[start + n - 1].necessary > 0)) {
 		fprintf(stderr, "endpoints not marked necessary\n");
 		exit(EXIT_IMPOSSIBLE);
 	}
 
 	int prev = 0;
 	for (int here = 1; here < n; here++) {
-		if (geom[start + here].necessary) {
+		if (geom[start + here].necessary > 0) {
 			recursion_stack.push(prev);
 			recursion_stack.push(here);
 			prev = here;
@@ -829,9 +829,12 @@ void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, siz
 		if (geom[start + first] < geom[start + second]) {
 			farthest_element_index = first;
 			for (i = first + 1; i < second; i++) {
-				double temp_dist = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + first].x, geom[start + first].y, geom[start + second].x, geom[start + second].y);
+				double distance;
-
+				if (geom[start + i].necessary < 0) {
-				double distance = std::fabs(temp_dist);
+					distance = 0;
+				} else {
+					distance = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + first].x, geom[start + first].y, geom[start + second].x, geom[start + second].y);
+				}
 
 				if ((distance > e || kept < retain) && (distance > max_distance || (distance == max_distance && geom[start + i] < geom[start + farthest_element_index]))) {
 					farthest_element_index = i;
@@ -841,9 +844,12 @@ void douglas_peucker(drawvec &geom, int start, int n, double e, size_t kept, siz
 		} else {
 			farthest_element_index = second;
 			for (i = second - 1; i > first; i--) {
-				double temp_dist = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + second].x, geom[start + second].y, geom[start + first].x, geom[start + first].y);
+				double distance;
-
+				if (geom[start + i].necessary < 0) {
-				double distance = std::fabs(temp_dist);
+					distance = 0;
+				} else {
+					distance = distance_from_line(geom[start + i].x, geom[start + i].y, geom[start + second].x, geom[start + second].y, geom[start + first].x, geom[start + first].y);
+				}
 
 				if ((distance > e || kept < retain) && (distance > max_distance || (distance == max_distance && geom[start + i] < geom[start + farthest_element_index]))) {
 					farthest_element_index = i;
@@ -917,7 +923,7 @@ static drawvec simplify_lines_basic(drawvec &geom, int z, int detail, double sim
 
 	size_t out = 0;
 	for (size_t i = 0; i < geom.size(); i++) {
-		if (geom[i].necessary) {
+		if (geom[i].necessary > 0) {
 			geom[out++] = geom[i];
 		}
 	}

geometry.cpp

@@ -239,6 +239,48 @@ drawvec impose_tile_boundaries(const drawvec &geom, long long extent) {
 	return out;
 }
 
+static void mark_unnecessary(drawvec &geom, size_t start, size_t end, double e) {
+	double ee = e * e;
+
+	if (geom[start] < geom[end]) {
+		size_t last = start;
+		for (size_t i = start + 1; i < end; i++) {
+			long long dx = geom[i].x - geom[last].x;
+			long long dy = geom[i].y - geom[last].y;
+			if (dx * dx + dy * dy < ee) {
+				geom[i].necessary = -1;
+			} else {
+				last = i;
+			}
+		}
+	} else {
+		size_t last = end;
+		for (size_t i = end - 1; i > start; i--) {
+			long long dx = geom[i].x - geom[last].x;
+			long long dy = geom[i].y - geom[last].y;
+			if (dx * dx + dy * dy < ee) {
+				geom[i].necessary = -1;
+			} else {
+				last = i;
+			}
+		}
+	}
+}
+
+static void mark_unnecessary(drawvec &geom, double e) {
+	for (size_t i = 0; i < geom.size(); i++) {
+		if (geom[i].necessary > 0) {
+			for (size_t j = i + 1; j < geom.size(); j++) {
+				if (geom[j].necessary > 0) {
+					mark_unnecessary(geom, i, j, e);
+					i = j - 1;
+					break;
+				}
+			}
+		}
+	}
+}
+
 drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool mark_tile_bounds, double simplification, size_t retain, drawvec const &shared_nodes, struct node *shared_nodes_map, size_t nodepos, std::string const &shared_nodes_bloom) {
 	int res = 1 << (32 - detail - z);
 	long long area = 1LL << (32 - z);
@@ -265,7 +307,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 
 			auto pt = std::lower_bound(shared_nodes.begin(), shared_nodes.end(), geom[i]);
 			if (pt != shared_nodes.end() && *pt == geom[i]) {
-				geom[i].necessary = true;
+				geom[i].necessary = 1;
 			}
 
 			if (nodepos > 0) {
@@ -284,7 +326,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 
 				if (shared_nodes_bloom[bloom_ix] & bloom_mask) {
 					if (bsearch(&n, shared_nodes_map, nodepos / sizeof(node), sizeof(node), nodecmp) != NULL) {
-						geom[i].necessary = true;
+						geom[i].necessary = 1;
 					}
 				}
 			}
@@ -295,6 +337,10 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 		geom = impose_tile_boundaries(geom, area);
 	}
 
+	if (!additional[A_VISVALINGAM]) {
+		mark_unnecessary(geom, res * simplification);
+	}
+
 	for (size_t i = 0; i < geom.size(); i++) {
 		if (geom[i].op == VT_MOVETO) {
 			size_t j;
@@ -327,7 +373,7 @@ drawvec simplify_lines(drawvec &geom, int z, int tx, int ty, int detail, bool ma
 
 	size_t out = 0;
 	for (size_t i = 0; i < geom.size(); i++) {
-		if (geom[i].necessary) {
+		if (geom[i].necessary > 0) {
 			geom[out++] = geom[i];
 		}
 	}