From e154a94ef0225a556e81a9ce0f464b8a85bb51c6 Mon Sep 17 00:00:00 2001
From: John Firebaugh <john.firebaugh@gmail.com>
Date: Sun, 17 Feb 2013 11:06:36 -0800
Subject: [PATCH] Draw only visible midpoints (#804)

---
 js/id/renderer/map.js  |  2 +-
 js/id/svg/midpoints.js | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/js/id/renderer/map.js b/js/id/renderer/map.js
index d4c082fad..be4366355 100644
--- a/js/id/renderer/map.js
+++ b/js/id/renderer/map.js
@@ -89,7 +89,7 @@ iD.Map = function(context) {
                 .call(vertices, graph, all, filter)
                 .call(lines, graph, all, filter)
                 .call(areas, graph, all, filter)
-                .call(midpoints, graph, all, filter)
+                .call(midpoints, graph, all, filter, extent)
                 .call(labels, graph, all, filter, dimensions, !difference);
         }
         dispatch.drawn(map);
diff --git a/js/id/svg/midpoints.js b/js/id/svg/midpoints.js
index fc1a5bbc3..8dc6d09b9 100644
--- a/js/id/svg/midpoints.js
+++ b/js/id/svg/midpoints.js
@@ -1,5 +1,5 @@
 iD.svg.Midpoints = function(projection) {
-    return function drawMidpoints(surface, graph, entities, filter) {
+    return function drawMidpoints(surface, graph, entities, filter, extent) {
         var midpoints = {};
 
         if (!surface.select('.layer-hit g.vertex').node()) {
@@ -22,13 +22,16 @@ iD.svg.Midpoints = function(projection) {
                 if (midpoints[id]) {
                     midpoints[id].ways.push({id: entity.id, index: j + 1});
 
-                } else if (iD.geo.dist(projection(a.loc), projection(b.loc)) > 40) {
-                    midpoints[id] = {
-                        type: 'midpoint',
-                        id: id,
-                        loc: iD.geo.interp(a.loc, b.loc, 0.5),
-                        ways: [{id: entity.id, index: j + 1}]
-                    };
+                } else {
+                    var loc = iD.geo.interp(a.loc, b.loc, 0.5);
+                    if (extent.intersects(loc) && iD.geo.dist(projection(a.loc), projection(b.loc)) > 40) {
+                        midpoints[id] = {
+                            type: 'midpoint',
+                            id: id,
+                            loc: loc,
+                            ways: [{id: entity.id, index: j + 1}]
+                        };
+                    }
                 }
             }
         }