Add an option to extend zooms if still dropping, but with a limit

README.md

@@ -341,6 +341,8 @@ Parallel processing will also be automatic if the input file is in FlatGeobuf fo
  * `-ae` or `--extend-zooms-if-still-dropping`: Increase the maxzoom if features are still being dropped at that zoom level.
    The detail and simplification options that ordinarily apply only to the maximum zoom level will apply both to the originally
    specified maximum zoom and to any levels added beyond that.
+ * `extend-zooms-if-still-dropping-maximum=`_count_: Increase the maxzoom if features are still being dropped at that zoom level
+   by up to _count_ zoom levels.
  * `-R` _zoom_`/`_x_`/`_y_ or `--one-tile=`_zoom_`/`_x_`/`_y_: Set the minzoom and maxzoom to _zoom_ and produce only
    the single specified tile at that zoom level.
 

main.cpp

@@ -91,6 +91,7 @@ size_t limit_tile_feature_count_at_maxzoom = 0;
 unsigned int drop_denser = 0;
 std::map<std::string, serial_val> set_attributes;
 unsigned long long preserve_point_density_threshold = 0;
+long long extend_zooms_max = 0;
 
 std::vector<order_field> order_by;
 bool order_reverse;
@@ -2892,6 +2893,7 @@ int main(int argc, char **argv) {
 		{"minimum-zoom", required_argument, 0, 'Z'},
 		{"smallest-maximum-zoom-guess", required_argument, 0, '~'},
 		{"extend-zooms-if-still-dropping", no_argument, &additional[A_EXTEND_ZOOMS], 1},
+		{"extend-zooms-if-still-dropping-maximum", required_argument, 0, '~'},
 		{"one-tile", required_argument, 0, 'R'},
 
 		{"Tile resolution", 0, 0, 0},
@@ -3138,6 +3140,8 @@ int main(int argc, char **argv) {
 				}
 			} else if (strcmp(opt, "preserve-point-density-threshold") == 0) {
 				preserve_point_density_threshold = atoll_require(optarg, "Preserve point density threshold");
+            } else if (strcmp(opt, "extend-zooms-if-still-dropping-maximum") == 0) {
+				extend_zooms_max = atoll_require(optarg, "Maximum number by which to extend zooms");
 			} else {
 				fprintf(stderr, "%s: Unrecognized option --%s\n", argv[0], opt);
 				exit(EXIT_ARGS);

main.hpp

@@ -61,6 +61,7 @@ extern int tiny_polygon_size;
 extern size_t limit_tile_feature_count;
 extern size_t limit_tile_feature_count_at_maxzoom;
 extern std::map<std::string, serial_val> set_attributes;
+extern long long extend_zooms_max;
 
 struct order_field {
 	std::string name;

man/tippecanoe.1

@@ -403,6 +403,9 @@ Parallel processing will also be automatic if the input file is in FlatGeobuf fo
 The detail and simplification options that ordinarily apply only to the maximum zoom level will apply both to the originally
 specified maximum zoom and to any levels added beyond that.
 .IP \(bu 2
+\fB\fCextend\-zooms\-if\-still\-dropping\-maximum=\fR\fIcount\fP: Increase the maxzoom if features are still being dropped at that zoom level
+by up to \fIcount\fP zoom levels.
+.IP \(bu 2
 \fB\fC\-R\fR \fIzoom\fP\fB\fC/\fR\fIx\fP\fB\fC/\fR\fIy\fP or \fB\fC\-\-one\-tile=\fR\fIzoom\fP\fB\fC/\fR\fIx\fP\fB\fC/\fR\fIy\fP: Set the minzoom and maxzoom to \fIzoom\fP and produce only
 the single specified tile at that zoom level.
 .RE

tile.cpp

@@ -332,7 +332,7 @@ struct ordercmp {
 } ordercmp;
 
 void rewrite(drawvec &geom, int z, int nextzoom, int maxzoom, long long *bbox, unsigned tx, unsigned ty, int buffer, int *within, std::atomic<long long> *geompos, compressor **geomfile, const char *fname, signed char t, int layer, signed char feature_minzoom, int child_shards, int max_zoom_increment, long long seq, int tippecanoe_minzoom, int tippecanoe_maxzoom, int segment, unsigned *initial_x, unsigned *initial_y, std::vector<long long> &metakeys, std::vector<long long> &metavals, bool has_id, unsigned long long id, unsigned long long index, unsigned long long label_point, long long extent) {
-	if (geom.size() > 0 && (nextzoom <= maxzoom || additional[A_EXTEND_ZOOMS])) {
+	if (geom.size() > 0 && (nextzoom <= maxzoom || additional[A_EXTEND_ZOOMS] || extend_zooms_max > 0)) {
 		int xo, yo;
 		int span = 1 << (nextzoom - z);
 
@@ -3238,9 +3238,14 @@ int traverse_zooms(int *geomfd, off_t *geom_size, char *stringpool, std::atomic<
 					z = args[thread].wrote_zoom;
 				}
 
-				if (additional[A_EXTEND_ZOOMS] && z == maxzoom && args[thread].still_dropping && maxzoom < MAX_ZOOM) {
-					maxzoom++;
-				}
+                if (args[thread].still_dropping) {
+                    if (additional[A_EXTEND_ZOOMS] && z == maxzoom && maxzoom < MAX_ZOOM) {
+                        maxzoom++;
+                    } else if (extend_zooms_max > 0 && z == maxzoom && maxzoom < MAX_ZOOM) {
+                        maxzoom++;
+                        extend_zooms_max--;
+                    }
+                }
 			}
 
 			if ((size_t) z >= strategies.size()) {