From 51be28707f59096e254b074b24ec86ccbb19749b Mon Sep 17 00:00:00 2001
From: Vladimir Agafonkin <agafonkin@gmail.com>
Date: Thu, 9 Jun 2016 18:18:55 +0300
Subject: [PATCH] rewind polygons for vt2 compliance

---
 src/clip.js                      | 14 ++++++++------
 src/convert.js                   | 10 +++++++---
 src/tile.js                      | 17 +++++++++++++++++
 test/fixtures/feature-tiles.json |  2 +-
 4 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/src/clip.js b/src/clip.js
index f657ad8..3697c0d 100644
--- a/src/clip.js
+++ b/src/clip.js
@@ -78,6 +78,7 @@ function clipGeometry(geometry, k1, k2, axis, intersect, closed) {
             points = geometry[i],
             area = points.area,
             dist = points.dist,
+            outer = points.outer,
             len = points.length,
             a, j, last;
 
@@ -93,7 +94,7 @@ function clipGeometry(geometry, k1, k2, axis, intersect, closed) {
 
                 if ((bk > k2)) { // ---|-----|-->
                     slice.push(intersect(a, b, k1), intersect(a, b, k2));
-                    if (!closed) slice = newSlice(slices, slice, area, dist);
+                    if (!closed) slice = newSlice(slices, slice, area, dist, outer);
 
                 } else if (bk >= k1) slice.push(intersect(a, b, k1)); // ---|-->  |
 
@@ -101,7 +102,7 @@ function clipGeometry(geometry, k1, k2, axis, intersect, closed) {
 
                 if ((bk < k1)) { // <--|-----|---
                     slice.push(intersect(a, b, k2), intersect(a, b, k1));
-                    if (!closed) slice = newSlice(slices, slice, area, dist);
+                    if (!closed) slice = newSlice(slices, slice, area, dist, outer);
 
                 } else if (bk <= k2) slice.push(intersect(a, b, k2)); // |  <--|---
 
@@ -111,11 +112,11 @@ function clipGeometry(geometry, k1, k2, axis, intersect, closed) {
 
                 if (bk < k1) { // <--|---  |
                     slice.push(intersect(a, b, k1));
-                    if (!closed) slice = newSlice(slices, slice, area, dist);
+                    if (!closed) slice = newSlice(slices, slice, area, dist, outer);
 
                 } else if (bk > k2) { // |  ---|-->
                     slice.push(intersect(a, b, k2));
-                    if (!closed) slice = newSlice(slices, slice, area, dist);
+                    if (!closed) slice = newSlice(slices, slice, area, dist, outer);
                 }
                 // | --> |
             }
@@ -132,18 +133,19 @@ function clipGeometry(geometry, k1, k2, axis, intersect, closed) {
         if (closed && last && (slice[0][0] !== last[0] || slice[0][1] !== last[1])) slice.push(slice[0]);
 
         // add the final slice
-        newSlice(slices, slice, area, dist);
+        newSlice(slices, slice, area, dist, outer);
     }
 
     return slices;
 }
 
-function newSlice(slices, slice, area, dist) {
+function newSlice(slices, slice, area, dist, outer) {
     if (slice.length) {
         // we don't recalculate the area/length of the unclipped geometry because the case where it goes
         // below the visibility threshold as a result of clipping is rare, so we avoid doing unnecessary work
         slice.area = area;
         slice.dist = dist;
+        if (outer !== undefined) slice.outer = outer;
 
         slices.push(slice);
     }
diff --git a/src/convert.js b/src/convert.js
index 26f0cbb..3a238ff 100644
--- a/src/convert.js
+++ b/src/convert.js
@@ -33,7 +33,7 @@ function convertFeature(features, feature, tolerance) {
         type = geom.type,
         coords = geom.coordinates,
         tags = feature.properties,
-        i, j, rings;
+        i, j, rings, projectedRing;
 
     if (type === 'Point') {
         features.push(create(tags, 1, [projectPoint(coords)]));
@@ -47,7 +47,9 @@ function convertFeature(features, feature, tolerance) {
     } else if (type === 'MultiLineString' || type === 'Polygon') {
         rings = [];
         for (i = 0; i < coords.length; i++) {
-            rings.push(project(coords[i], tolerance));
+            projectedRing = project(coords[i], tolerance);
+            if (type === 'Polygon') projectedRing.outer = (i === 0);
+            rings.push(projectedRing);
         }
         features.push(create(tags, type === 'Polygon' ? 3 : 2, rings));
 
@@ -55,7 +57,9 @@ function convertFeature(features, feature, tolerance) {
         rings = [];
         for (i = 0; i < coords.length; i++) {
             for (j = 0; j < coords[i].length; j++) {
-                rings.push(project(coords[i][j], tolerance));
+                projectedRing = project(coords[i][j], tolerance);
+                projectedRing.outer = (j === 0);
+                rings.push(projectedRing);
             }
         }
         features.push(create(tags, 3, rings));
diff --git a/src/tile.js b/src/tile.js
index 4e6ccb1..818383b 100644
--- a/src/tile.js
+++ b/src/tile.js
@@ -71,6 +71,8 @@ function addFeature(tile, feature, tolerance, noSimplify) {
                 tile.numPoints++;
             }
 
+            if (type === 3) rewind(simplifiedRing, ring.outer);
+
             simplified.push(simplifiedRing);
         }
     }
@@ -83,3 +85,18 @@ function addFeature(tile, feature, tolerance, noSimplify) {
         });
     }
 }
+
+function rewind(ring, clockwise) {
+    var area = signedArea(ring);
+    if (area < 0 === clockwise) ring.reverse();
+}
+
+function signedArea(ring) {
+    var sum = 0;
+    for (var i = 0, len = ring.length, j = len - 1, p1, p2; i < len; j = i++) {
+        p1 = ring[i];
+        p2 = ring[j];
+        sum += (p2[0] - p1[0]) * (p1[1] + p2[1]);
+    }
+    return sum;
+}
diff --git a/test/fixtures/feature-tiles.json b/test/fixtures/feature-tiles.json
index 6014550..7da54d8 100644
--- a/test/fixtures/feature-tiles.json
+++ b/test/fixtures/feature-tiles.json
@@ -1 +1 @@
-{"z0-0-0":[{"geometry":[[[3186,2048],[3197,2048],[3197,2037],[3186,2037],[3186,2048]]],"type":3,"tags":{"prop0":"value0","prop1":{"this":"that"}}}]}
+{"z0-0-0":[{"geometry":[[[3186,2048],[3186,2037],[3197,2037],[3197,2048],[3186,2048]]],"type":3,"tags":{"prop0":"value0","prop1":{"this":"that"}}}]}