From 18cdcb07325f77c6ab3cc780b7c3f72466c143f0 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Wed, 1 Jul 2015 12:16:50 -0700
Subject: [PATCH] Drop linetos smaller than tile resolution before doing normal
 simplification

Since simplification is rather expensive
---
 geometry.cc | 10 +++++-----
 geometry.hh |  2 +-
 tile.cc     | 10 +++++++---
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/geometry.cc b/geometry.cc
index 281a41c..b0f2e86 100644
--- a/geometry.cc
+++ b/geometry.cc
@@ -84,7 +84,7 @@ void to_tile_scale(drawvec &geom, int z, int detail) {
 	}
 }
 
-drawvec remove_noop(drawvec geom, int type) {
+drawvec remove_noop(drawvec geom, int type, int shift) {
 	// first pass: remove empty linetos
 
 	long long x = 0, y = 0;
@@ -92,7 +92,7 @@ drawvec remove_noop(drawvec geom, int type) {
 	unsigned i;
 
 	for (i = 0; i < geom.size(); i++) {
-		if (geom[i].op == VT_LINETO && geom[i].x == x && geom[i].y == y) {
+		if (geom[i].op == VT_LINETO && (geom[i].x >> shift) == x && (geom[i].y >> shift) == y) {
 			continue;
 		}
 
@@ -100,8 +100,8 @@ drawvec remove_noop(drawvec geom, int type) {
 			out.push_back(geom[i]);
 		} else { /* moveto or lineto */
 			out.push_back(geom[i]);
-			x = geom[i].x;
-			y = geom[i].y;
+			x = geom[i].x >> shift;
+			y = geom[i].y >> shift;
 		}
 	}
 
@@ -137,7 +137,7 @@ drawvec remove_noop(drawvec geom, int type) {
 
 		for (i = 0; i < geom.size(); i++) {
 			if (geom[i].op == VT_MOVETO) {
-				if (i > 0 && geom[i - 1].op == VT_LINETO && geom[i - 1].x == geom[i].x && geom[i - 1].y == geom[i].y) {
+				if (i > 0 && geom[i - 1].op == VT_LINETO && (geom[i - 1].x >> shift) == (geom[i].x >> shift) && (geom[i - 1].y >> shift) == (geom[i].y >> shift)) {
 					continue;
 				}
 			}
diff --git a/geometry.hh b/geometry.hh
index b4cb3e9..8848e40 100644
--- a/geometry.hh
+++ b/geometry.hh
@@ -18,7 +18,7 @@ typedef std::vector<draw> drawvec;
 
 drawvec decode_geometry(char **meta, int z, unsigned tx, unsigned ty, int detail, long long *bbox);
 void to_tile_scale(drawvec &geom, int z, int detail);
-drawvec remove_noop(drawvec geom, int type);
+drawvec remove_noop(drawvec geom, int type, int shift);
 drawvec clip_point(drawvec &geom, int z, int detail, long long buffer);
 drawvec clip_poly(drawvec &geom, int z, int detail, int buffer);
 drawvec reduce_tiny_poly(drawvec &geom, int z, int detail, bool *reduced, double *accum_area);
diff --git a/tile.cc b/tile.cc
index 1c36762..8f1b42f 100644
--- a/tile.cc
+++ b/tile.cc
@@ -236,7 +236,7 @@ mapnik::vector::tile create_tile(char **layernames, int line_detail, std::vector
 		unsigned x;
 		for (x = 0; x < features[i].size(); x++) {
 			if (features[i][x].type == VT_LINE || features[i][x].type == VT_POLYGON) {
-				features[i][x].geom = remove_noop(features[i][x].geom, features[i][x].type);
+				features[i][x].geom = remove_noop(features[i][x].geom, features[i][x].type, 0);
 			}
 
 			mapnik::vector::tile_feature *feature = layer->add_features();
@@ -546,7 +546,7 @@ long long write_tile(char **geoms, char *metabase, char *stringpool, unsigned *f
 					geom = clip_point(geom, z, line_detail, buffer);
 				}
 
-				geom = remove_noop(geom, t);
+				geom = remove_noop(geom, t, 0);
 			}
 
 			if (geom.size() > 0) {
@@ -620,6 +620,10 @@ long long write_tile(char **geoms, char *metabase, char *stringpool, unsigned *f
 
 			if ((t == VT_LINE || t == VT_POLYGON) && !prevent['s' & 0xFF]) {
 				if (!reduced) {
+					if (t == VT_LINE) {
+						geom = remove_noop(geom, t, 32 - z - line_detail);
+					}
+
 					geom = simplify_lines(geom, z, line_detail);
 				}
 			}
@@ -701,7 +705,7 @@ long long write_tile(char **geoms, char *metabase, char *stringpool, unsigned *f
 
 			for (x = 0; x < features[j].size(); x++) {
 				if (features[j][x].coalesced && features[j][x].type == VT_LINE) {
-					features[j][x].geom = remove_noop(features[j][x].geom, features[j][x].type);
+					features[j][x].geom = remove_noop(features[j][x].geom, features[j][x].type, 0);
 					features[j][x].geom = simplify_lines(features[j][x].geom, 32, 0);
 				}
 			}