Add an option to dynamically increase gamma until tiles are small enough

README.md

@@ -126,6 +126,7 @@ resolution is obtained than by using a smaller _maxzoom_ or _detail_.
  * -ap or --drop-polygons: Let "dot" dropping at lower zooms apply to polygons too
  * -ag or --calculate-feature-density: Add a new attribute, `tippecanoe_feature_density`, to each feature, to record how densely features are spaced in that area of the tile. You can use this attribute in the style to produce a glowing effect where points are densely packed. It can range from 0 in the sparsest areas to 255 in the densest.
  * -ab or --detect-shared-borders: In the manner of [TopoJSON](https://github.com/mbostock/topojson/wiki/Introduction), detect borders that are shared between multiple polygons and simplify them identically in each polygon. This takes more time and memory than considering each polygon individually.
+ * -aG or --increase-gamma-as-needed: If a tile is too large, try to reduce it to under 500K by increasing the `-g` gamma
 
 ### Doing less
 

main.cpp

@@ -1911,6 +1911,7 @@ int main(int argc, char **argv) {
 		{"prefer-radix-sort", no_argument, &additional[A_PREFER_RADIX_SORT], 1},
 		{"calculate-feature-density", no_argument, &additional[A_CALCULATE_FEATURE_DENSITY], 1},
 		{"detect-shared-borders", no_argument, &additional[A_DETECT_SHARED_BORDERS], 1},
+		{"increase-gamma-as-needed", no_argument, &additional[A_INCREASE_GAMMA_AS_NEEDED], 1},
 
 		{"no-line-simplification", no_argument, &prevent[P_SIMPLIFY], 1},
 		{"simplify-only-low-zooms", no_argument, &prevent[P_SIMPLIFY_LOW], 1},

man/tippecanoe.1

@@ -150,6 +150,8 @@ which may not be what you want.
 \-ag or \-\-calculate\-feature\-density: Add a new attribute, \fB\fCtippecanoe_feature_density\fR, to each feature, to record how densely features are spaced in that area of the tile. You can use this attribute in the style to produce a glowing effect where points are densely packed. It can range from 0 in the sparsest areas to 255 in the densest.
 .IP \(bu 2
 \-ab or \-\-detect\-shared\-borders: In the manner of TopoJSON \[la]https://github.com/mbostock/topojson/wiki/Introduction\[ra], detect borders that are shared between multiple polygons and simplify them identically in each polygon. This takes more time and memory than considering each polygon individually.
+.IP \(bu 2
+\-aG or \-\-increase\-gamma\-as\-needed: If a tile is too large, try to reduce it to under 500K by increasing the \fB\fC\-g\fR gamma
 .RE
 .SS Doing less
 .RS

options.hpp

@@ -7,6 +7,7 @@
 #define A_DETECT_SHARED_BORDERS ((int) 'b')
 #define A_PREFER_RADIX_SORT ((int) 'R')
 #define A_CALCULATE_FEATURE_DENSITY ((int) 'g')
+#define A_INCREASE_GAMMA_AS_NEEDED ((int) 'G')
 
 #define P_SIMPLIFY ((int) 's')
 #define P_SIMPLIFY_LOW ((int) 'S')

tile.cpp

@@ -990,6 +990,7 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 
 	static volatile double oprogress = 0;
 
+	bool first_time = true;
 	// This only loops if the tile data didn't fit, in which case the detail
 	// goes down and the progress indicator goes backward for the next try.
 	for (line_detail = detail; line_detail >= min_detail || line_detail == detail; line_detail--, oprogress = 0) {
@@ -1177,7 +1178,7 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 				unclipped_features++;
 			}
 
-			if (line_detail == detail && fraction == 1) { /* only write out the next zoom once, even if we retry */
+			if (first_time) { /* only write out the next zoom once, even if we retry */
 				rewrite(geom, z, nextzoom, maxzoom, bbox, tx, ty, buffer, line_detail, within, geompos, geomfile, fname, t, layer, metastart, feature_minzoom, child_shards, max_zoom_increment, original_seq, tippecanoe_minzoom, tippecanoe_maxzoom, segment, initial_x, initial_y, m, metakeys, metavals, has_id, id);
 			}
 
@@ -1253,6 +1254,8 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 			}
 		}
 
+		first_time = false;
+
 		if (additional[A_DETECT_SHARED_BORDERS]) {
 			find_common_edges(partials, z, line_detail, simplification, maxzoom);
 		}
@@ -1473,8 +1476,30 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 		if (totalsize > 0 && tile.layers.size() > 0) {
 			if (totalsize > 200000 && !prevent[P_FEATURE_LIMIT]) {
 				fprintf(stderr, "tile %d/%u/%u has %lld features, >200000    \n", z, tx, ty, totalsize);
-				fprintf(stderr, "Try using -B to set a higher base zoom level.\n");
-				return -1;
+
+				if (prevent[P_DYNAMIC_DROP]) {
+					fraction = fraction * 200000 / totalsize * 0.95;
+					if (!quiet) {
+						fprintf(stderr, "Going to try keeping %0.2f%% of the features to make it fit\n", fraction * 100);
+					}
+					line_detail++;  // to keep it the same when the loop decrements it
+					continue;
+				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED]) {
+					if (gamma < 1) {
+						gamma = 1;
+					} else {
+						gamma = gamma * 1.25;
+					}
+
+					if (!quiet) {
+						fprintf(stderr, "Going to try gamma of %0.3f to make it fit\n", gamma);
+					}
+					line_detail++;  // to keep it the same when the loop decrements it
+					continue;
+				} else {
+					fprintf(stderr, "Try using -B (and --drop-lines or --drop-polygons if needed) to set a higher base zoom level.\n");
+					return -1;
+				}
 			}
 
 			std::string compressed = tile.encode();
@@ -1493,6 +1518,17 @@ long long write_tile(FILE *geoms, long long *geompos_in, char *metabase, char *s
 						fprintf(stderr, "Going to try keeping %0.2f%% of the features to make it fit\n", fraction * 100);
 					}
 					line_detail++;  // to keep it the same when the loop decrements it
+				} else if (additional[A_INCREASE_GAMMA_AS_NEEDED]) {
+					if (gamma < 1) {
+						gamma = 1;
+					} else {
+						gamma = gamma * 1.25;
+					}
+
+					if (!quiet) {
+						fprintf(stderr, "Going to try gamma of %0.3f to make it fit\n", gamma);
+					}
+					line_detail++;  // to keep it the same when the loop decrements it
 				}
 			} else {
 				if (pthread_mutex_lock(&db_lock) != 0) {