Always include the very first and last points for fills

src/traces/scatter/line_points.js

@@ -31,9 +31,11 @@ module.exports = function linePoints(d, opts) {
     var baseTolerance = opts.baseTolerance;
     var shape = opts.shape;
     var linear = shape === 'linear';
+    var fill = opts.fill && opts.fill !== 'none';
     var segments = [];
     var minTolerance = constants.minTolerance;
-    var pts = new Array(d.length);
+    var len = d.length;
+    var pts = new Array(len);
     var pti = 0;
 
     var i;
@@ -160,8 +162,10 @@ module.exports = function linePoints(d, opts) {
         var ptCount = 0;
         for(var i = 0; i < 4; i++) {
             var edge = edges[i];
-            var ptInt = segmentsIntersect(pt1[0], pt1[1], pt2[0], pt2[1],
-                edge[0], edge[1], edge[2], edge[3]);
+            var ptInt = segmentsIntersect(
+                pt1[0], pt1[1], pt2[0], pt2[1],
+                edge[0], edge[1], edge[2], edge[3]
+            );
             if(ptInt && (!ptCount ||
                 Math.abs(ptInt.x - out[0][0]) > 1 ||
                 Math.abs(ptInt.y - out[0][1]) > 1
@@ -359,7 +363,7 @@ module.exports = function linePoints(d, opts) {
     }
 
     // loop over ALL points in this trace
-    for(i = 0; i < d.length; i++) {
+    for(i = 0; i < len; i++) {
         clusterStartPt = getPt(i);
         if(!clusterStartPt) continue;
 
@@ -368,7 +372,7 @@ module.exports = function linePoints(d, opts) {
         addPt(clusterStartPt);
 
         // loop over one segment of the trace
-        for(i++; i < d.length; i++) {
+        for(i++; i < len; i++) {
             clusterHighPt = getPt(i);
             if(!clusterHighPt) {
                 if(connectGaps) continue;
@@ -387,7 +391,9 @@ module.exports = function linePoints(d, opts) {
 
             clusterRefDist = ptDist(clusterHighPt, clusterStartPt);
 
-            if(clusterRefDist < getTolerance(clusterHighPt, nextPt) * minTolerance) continue;
+            // #3147 - always include the very first and last points for fills
+            if(!(fill && (pti === 0 || pti === len - 1)) &&
+                clusterRefDist < getTolerance(clusterHighPt, nextPt) * minTolerance) continue;
 
             clusterUnitVector = [
                 (clusterHighPt[0] - clusterStartPt[0]) / clusterRefDist,

src/traces/scatter/plot.js

@@ -225,7 +225,8 @@ function plotOne(gd, idx, plotinfo, cdscatter, cdscatterAll, element, transition
             connectGaps: trace.connectgaps,
             baseTolerance: Math.max(line.width || 1, 3) / 4,
             shape: line.shape,
-            simplify: line.simplify
+            simplify: line.simplify,
+            fill: trace.fill
         });
 
         // since we already have the pixel segments here, use them to make

test/image/mocks/ultra_zoom_fill.json

@@ -0,0 +1,21 @@
+{
+  "data": [
+    {
+      "name": 10000,
+      "fill": "toself",
+      "x": [ 1, 10, 10, 1 ],
+      "y": [ 10000, 10000, -10000, -10000 ]
+    },
+    {
+      "fill": "toself",
+      "name": 100,
+      "x": [ 1, 10, 10, 1 ],
+      "y": [ 100, 100, -100, -100 ]
+    }
+  ],
+  "layout": {
+    "yaxis": {
+      "range": [ -0.5, 0.5 ]
+    }
+  }
+}