From 9eb3a7f7ecfa84852d70a98dbd4070f1bcc502b8 Mon Sep 17 00:00:00 2001
From: Eric Fischer <enf@pobox.com>
Date: Fri, 5 May 2017 10:56:50 -0700
Subject: [PATCH] Enforce polygon winding and closure rules in
 tippecanoe-decode

---
 CHANGELOG.md     |  4 ++++
 README.md        |  1 +
 decode.cpp       | 23 ++++++++++++++++++++++-
 man/tippecanoe.1 |  2 ++
 version.hpp      |  2 +-
 5 files changed, 30 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67ef478..00cf0ba 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.17.7
+
+* Enforce polygon winding and closure rules in tippecanoe-decode
+
 ## 1.17.6
 
 * Add tile-join options to set name, attribution, description
diff --git a/README.md b/README.md
index c536122..0d5745e 100644
--- a/README.md
+++ b/README.md
@@ -482,3 +482,4 @@ resolutions.
  * `-z` _maxzoom_: Specify the highest zoom level to decode from the tileset
  * `-Z` _minzoom_: Specify the lowest zoom level to decode from the tileset
  * `-l` _layer_: Decode only layers with the specified names. (Multiple `-l` options can be specified.)
+ * `-f`: Decode tiles even if polygon ring order or closure problems are detected
diff --git a/decode.cpp b/decode.cpp
index cc84daf..c55288e 100644
--- a/decode.cpp
+++ b/decode.cpp
@@ -19,6 +19,7 @@
 
 int minzoom = 0;
 int maxzoom = 32;
+bool force = false;
 
 void printq(const char *s) {
 	putchar('"');
@@ -261,6 +262,15 @@ void handle(std::string message, int z, unsigned x, unsigned y, int describe, st
 							rings[n].push_back(ops[i]);
 						}
 					}
+
+					if (i >= ops.size() || ops[i + 1].op == VT_MOVETO) {
+						if (ops[i].op != VT_CLOSEPATH) {
+							fprintf(stderr, "Ring does not end with closepath (ends with %d)\n", ops[i].op);
+							if (!force) {
+								exit(EXIT_FAILURE);
+							}
+						}
+					}
 				}
 
 				int outer = 0;
@@ -290,6 +300,13 @@ void handle(std::string message, int z, unsigned x, unsigned y, int describe, st
 
 				int state = 0;
 				for (size_t i = 0; i < rings.size(); i++) {
+					if (i == 0 && areas[i] < 0) {
+						fprintf(stderr, "Polygon begins with an inner ring\n");
+						if (!force) {
+							exit(EXIT_FAILURE);
+						}
+					}
+
 					if (areas[i] >= 0) {
 						if (state != 0) {
 							// new multipolygon
@@ -489,7 +506,7 @@ int main(int argc, char **argv) {
 	int i;
 	std::set<std::string> to_decode;
 
-	while ((i = getopt(argc, argv, "t:Z:z:l:")) != -1) {
+	while ((i = getopt(argc, argv, "t:Z:z:l:f")) != -1) {
 		switch (i) {
 		case 't':
 			set_projection_or_exit(optarg);
@@ -507,6 +524,10 @@ int main(int argc, char **argv) {
 			to_decode.insert(optarg);
 			break;
 
+		case 'f':
+			force = true;
+			break;
+
 		default:
 			usage(argv);
 		}
diff --git a/man/tippecanoe.1 b/man/tippecanoe.1
index 010a659..167a114 100644
--- a/man/tippecanoe.1
+++ b/man/tippecanoe.1
@@ -568,4 +568,6 @@ resolutions.
 \fB\fC\-Z\fR \fIminzoom\fP: Specify the lowest zoom level to decode from the tileset
 .IP \(bu 2
 \fB\fC\-l\fR \fIlayer\fP: Decode only layers with the specified names. (Multiple \fB\fC\-l\fR options can be specified.)
+.IP \(bu 2
+\fB\fC\-f\fR: Decode tiles even if polygon ring order or closure problems are detected
 .RE
diff --git a/version.hpp b/version.hpp
index 22946d4..c70088e 100644
--- a/version.hpp
+++ b/version.hpp
@@ -1 +1 @@
-#define VERSION "tippecanoe v1.17.6\n"
+#define VERSION "tippecanoe v1.17.7\n"