Remove unnecessary holes from output

src/connect_edges.js

@@ -96,7 +96,13 @@ function initializeContourFromContext(event, contours, contourId) {
     // in an earlier iteration, otherwise it wouldn't be possible that it is "previous in
     // result".
     const lowerContourId = prevInResult.outputContourId;
-    const lowerResultTransition = prevInResult.resultTransition;
+    let lowerResultTransition = prevInResult.resultTransition;
+    if (!event.isExteriorRing && !event.isSubject) {
+      contour.cull = true;
+    } else if (!event.isExteriorRing && prevInResult.isExteriorRing) {
+      lowerResultTransition = 1;
+    }
+
     if (lowerResultTransition > 0) {
       // We are inside. Now we have to check if the thing below us is another hole or
       // an exterior contour.

src/index.js

@@ -80,7 +80,7 @@ export default function boolean(subject, clipping, operation) {
   const polygons = [];
   for (let i = 0; i < contours.length; i++) {
     let contour = contours[i];
-    if (contour.isExterior()) {
+    if (contour.isExterior() && contour.cull !== true) {
       // The exterior ring goes first
       let rings = [contour.points];
       // Followed by holes if any

test/fixtures/issue69.geojson

@@ -0,0 +1,21 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [[[2, 0],[10, 10],[10, 0],[2, 0]]]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "Polygon",
+        "coordinates": [[[5, 1],[12, 1],[12, 9],[5, 9],[5, 1]],[[6, 2],[11, 8],[6, 8],[6, 2]]]
+      }
+    }
+  ]
+}