From 6eb78a49196e461c9511589a0baf260351fc260c Mon Sep 17 00:00:00 2001
From: ldd <leonardoldd@gmail.com>
Date: Thu, 21 Nov 2019 21:09:25 -0500
Subject: [PATCH] add custom linear decimator
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Use Ramer–Douglas–Peucker algorithm
(https://en.wikipedia.org/wiki/Ramer%E2%80%93Douglas%E2%80%93Peucker_algorithm)

to decimate a linear line

Work in progress, consider this an idea, more than an actual commit
---
 src/traces/scatter/decimator.js   | 47 +++++++++++++++++++++++++++++++
 src/traces/scatter/line_points.js |  9 +++++-
 2 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 src/traces/scatter/decimator.js

diff --git a/src/traces/scatter/decimator.js b/src/traces/scatter/decimator.js
new file mode 100644
index 00000000000..b1a85091f82
--- /dev/null
+++ b/src/traces/scatter/decimator.js
@@ -0,0 +1,47 @@
+'use strict';
+
+var epsilon = 0.01;
+function perpendicularDistance(point, startingPoint, endPoint) {
+    if(!point || !startingPoint || !endPoint) return -1;
+    var x0 = point[0];
+    var y0 = point[1];
+    var x1 = startingPoint[0];
+    var y1 = startingPoint[1];
+    var x2 = endPoint[0];
+    var y2 = endPoint[1];
+
+    return (
+    Math.abs((y2 - y1) * x0 - (x2 - x1) * y0 + x2 * y1 - y2 * x1) /
+    Math.sqrt(Math.pow(y2 - y1, 2) + Math.pow(x2 - x1, 2))
+    );
+}
+
+module.exports = function douglasPeucker(points) {
+    // Find the point with the maximum distance
+    var dmax = 0;
+    var index = 0;
+    var end = points.length - 1;
+    for(var i = 0; i < end; i++) {
+        var d = perpendicularDistance(points[i], points[0], points[end]);
+        if(d > dmax) {
+            index = i;
+            dmax = d;
+        }
+    }
+
+    var simplifiedPoints = [];
+
+    // If max distance is greater than epsilon, recursively simplify
+    if(dmax > epsilon) {
+        // Recursive call
+        var partial1 = douglasPeucker(points.slice(0, index), epsilon);
+        var partial2 = douglasPeucker(points.slice(index, end + 1), epsilon);
+
+        // Build the result list
+        simplifiedPoints = partial1.slice(0, -1).concat(partial2);
+    } else {
+        simplifiedPoints = [points[0], points[end]];
+    }
+    // Return the result
+    return simplifiedPoints;
+};
diff --git a/src/traces/scatter/line_points.js b/src/traces/scatter/line_points.js
index 89964c92ccd..5ac61c76fa9 100644
--- a/src/traces/scatter/line_points.js
+++ b/src/traces/scatter/line_points.js
@@ -18,7 +18,7 @@ var Lib = require('../../lib');
 var segmentsIntersect = Lib.segmentsIntersect;
 var constrain = Lib.constrain;
 var constants = require('./constants');
-
+var linearSimplifier = require('./decimator');
 
 module.exports = function linePoints(d, opts) {
     var xa = opts.xaxis;
@@ -352,6 +352,13 @@ module.exports = function linePoints(d, opts) {
         }
     }
 
+    if(linear && opts.simplify) {
+        for(i = 0; i < len; i++) {
+            addPt(getPt(i));
+        }
+        return [linearSimplifier(pts)];
+    }
+
     // loop over ALL points in this trace
     for(i = 0; i < len; i++) {
         clusterStartPt = getPt(i);