From 105dfa73d79d752a59ff7bc13942f4a966931ef9 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Thu, 11 Dec 2014 13:34:50 -0800
Subject: [PATCH] Use bounding box for quick accept/reject before detailed
 clipping.

---
 geometry.cc | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 geometry.hh |  3 ++-
 tile.cc     | 27 ++++++++++++++++++---------
 3 files changed, 67 insertions(+), 11 deletions(-)

diff --git a/geometry.cc b/geometry.cc
index 8c4ad12..e74e970 100644
--- a/geometry.cc
+++ b/geometry.cc
@@ -8,6 +8,7 @@
 #include <unistd.h>
 #include <math.h>
 #include <sqlite3.h>
+#include <limits.h>
 #include "geometry.hh"
 
 extern "C" {
@@ -16,9 +17,14 @@ extern "C" {
 	#include "projection.h"
 }
 
-drawvec decode_geometry(char **meta, int z, unsigned tx, unsigned ty, int detail) {
+drawvec decode_geometry(char **meta, int z, unsigned tx, unsigned ty, int detail, long long *bbox) {
 	drawvec out;
 
+	bbox[0] = LONG_LONG_MAX;
+	bbox[1] = LONG_LONG_MAX;
+	bbox[2] = LONG_LONG_MIN;
+	bbox[3] = LONG_LONG_MIN;
+
 	while (1) {
 		draw d;
 
@@ -40,6 +46,19 @@ drawvec decode_geometry(char **meta, int z, unsigned tx, unsigned ty, int detail
 				wwy -= ty << (32 - z);
 			}
 
+			if (wwx < bbox[0]) {
+				bbox[0] = wwx;
+			}
+			if (wwy < bbox[1]) {
+				bbox[1] = wwy;
+			}
+			if (wwx > bbox[2]) {
+				bbox[2] = wwx;
+			}
+			if (wwy > bbox[3]) {
+				bbox[3] = wwy;
+			}
+
 			d.x = wwx;
 			d.y = wwy;
 		}
@@ -412,6 +431,33 @@ drawvec clip_point(drawvec &geom, int z, int detail, long long buffer) {
 	return out;
 }
 
+int quick_check(long long *bbox, int z, int detail, long long buffer) {
+	long long min = 0;
+	long long area = 0xFFFFFFFF;
+	if (z != 0) {
+		area = 1LL << (32 - z);
+
+		min -= buffer * area / 256;
+		area += buffer * area / 256;
+	}
+
+	// bbox entirely outside the tile
+	if (bbox[0] > area || bbox[1] > area) {
+		return 0;
+	}
+	if (bbox[2] < min || bbox[3] < min) {
+		return 0;
+	}
+
+	// bbox entirely within the tile
+	if (bbox[0] > min && bbox[1] > min && bbox[2] < area && bbox[3] < area) {
+		return 1;
+	}
+
+	// some overlap of edge
+	return 2;
+}
+
 drawvec clip_lines(drawvec &geom, int z, int detail, long long buffer) {
 	drawvec out;
 	unsigned i;
diff --git a/geometry.hh b/geometry.hh
index 9a1487b..d6fd72b 100644
--- a/geometry.hh
+++ b/geometry.hh
@@ -15,12 +15,13 @@ struct draw {
 
 typedef std::vector<draw> drawvec;
 
-drawvec decode_geometry(char **meta, int z, unsigned tx, unsigned ty, int detail);
+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 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);
 drawvec clip_lines(drawvec &geom, int z, int detail, long long buffer);
+int quick_check(long long *bbox, int z, int detail, long long buffer);
 drawvec simplify_lines(drawvec &geom, int z, int detail);
 drawvec reorder_lines(drawvec &geom);
diff --git a/tile.cc b/tile.cc
index 767eafc..c2cd1bb 100644
--- a/tile.cc
+++ b/tile.cc
@@ -386,25 +386,34 @@ long long write_tile(char **geoms, char *metabase, unsigned *file_bbox, int z, u
 			long long metastart;
 			deserialize_long_long(geoms, &metastart);
 			char *meta = metabase + metastart;
+			long long bbox[4];
 
-			drawvec geom = decode_geometry(geoms, z, tx, ty, line_detail);
+			drawvec geom = decode_geometry(geoms, z, tx, ty, line_detail, bbox);
 
 			signed char minzoom;
 			deserialize_byte(geoms, &minzoom);
 
+			int quick = quick_check(bbox, z, line_detail, buffer);
+			if (quick == 0) {
+				continue;
+			}
+
 #if 0
 			if (z > i->maxzoom) {
 				continue;
 			}
 #endif
-			if (t == VT_LINE) {
-				geom = clip_lines(geom, z, line_detail, buffer);
-			}
-			if (t == VT_POLYGON) {
-				geom = clip_poly(geom, z, line_detail, buffer);
-			}
-			if (t == VT_POINT) {
-				geom = clip_point(geom, z, line_detail, buffer);
+
+			if (quick != 1) {
+				if (t == VT_LINE) {
+					geom = clip_lines(geom, z, line_detail, buffer);
+				}
+				if (t == VT_POLYGON) {
+					geom = clip_poly(geom, z, line_detail, buffer);
+				}
+				if (t == VT_POINT) {
+					geom = clip_point(geom, z, line_detail, buffer);
+				}
 			}
 
 			geom = remove_noop(geom, t);