Support extreme off-plot data points in scatter lines

src/plot_api/plot_api.js

@@ -2734,12 +2734,8 @@ Plotly.purge = function purge(gd) {
     // remove plot container
     if(fullLayout._container) fullLayout._container.remove();
 
+    // in contrast to Plotly.Plots.purge which does NOT clear _context!
     delete gd._context;
-    delete gd._replotPending;
-    delete gd._mouseDownTime;
-    delete gd._legendMouseDownTime;
-    delete gd._hmpixcount;
-    delete gd._hmlumcount;
 
     return gd;
 };

src/plots/plots.js

@@ -1341,14 +1341,25 @@ plots.purge = function(gd) {
     delete gd._promises;
     delete gd._redrawTimer;
     delete gd.firstscatter;
-    delete gd.hmlumcount;
-    delete gd.hmpixcount;
+    delete gd._hmlumcount;
+    delete gd._hmpixcount;
     delete gd.numboxes;
     delete gd._transitionData;
     delete gd._transitioning;
     delete gd._initialAutoSize;
     delete gd._transitioningWithDuration;
 
+    // created during certain events, that *should* clean them up
+    // themselves, but may not if there was an error
+    delete gd._dragging;
+    delete gd._dragged;
+    delete gd._hoverdata;
+    delete gd._snapshotInProgress;
+    delete gd._editing;
+    delete gd._replotPending;
+    delete gd._mouseDownTime;
+    delete gd._legendMouseDownTime;
+
     // remove all event listeners
     if(gd.removeAllListeners) gd.removeAllListeners();
 };

src/traces/scatter/constants.js

@@ -10,5 +10,16 @@
 'use strict';
 
 module.exports = {
-    PTS_LINESONLY: 20
+    PTS_LINESONLY: 20,
+
+    // fixed parameters of clustering and clipping algorithms
+
+    // fraction of clustering tolerance "so close we don't even consider it a new point"
+    minTolerance: 0.2,
+    // how fast does clustering tolerance increase as you get away from the visible region
+    toleranceGrowth: 10,
+
+    // number of viewport sizes away from the visible region
+    // at which we clip all lines to the perimeter
+    maxScreensAway: 20
 };