finally explained how to lower the curve order

components/sections/drawing/handler.js

@@ -0,0 +1,85 @@
+var fit = require('../../../lib/curve-fitter.js');
+
+module.exports = {
+  setup: function(api) {
+    this.api = api;
+    this.reset();
+  },
+
+  reset: function() {
+    this.points = [];
+    this.curveset = false;
+    this.mode = 0;
+    if (this.api) {
+      let api = this.api;
+      api.setCurve(false);
+      api.reset();
+      api.redraw();
+    }
+  },
+
+  toggle: function() {
+    if (this.api) {
+      this.customTimeValues = false;
+      this.mode = (this.mode + 1) % fit.modes.length;
+      this.fitCurve(this.api);
+      this.api.redraw();
+    }
+  },
+
+  draw: function(api, curve) {
+    api.setPanelCount(1);
+    api.reset();
+    api.setColor('lightgrey');
+    api.drawGrid(10,10);
+
+    api.setColor('black');
+
+    if (!this.curveset && this.points.length > 2) {
+      curve = this.fitCurve(api);
+    }
+
+    if (curve) {
+      api.drawCurve(curve);
+      api.drawSkeleton(curve);
+    }
+
+    api.drawPoints(this.points);
+
+    if (!this.customTimeValues) {
+      api.setFill(0);
+      api.text("using "+fit.modes[this.mode]+" t values", {x: 5, y: 10});
+    }
+  },
+
+  processTimeUpdate(sliderid, timeValues) {
+    var api = this.api;
+    this.customTimeValues = true;
+    this.fitCurve(api, timeValues);
+    api.redraw();
+  },
+
+  fitCurve(api, timeValues) {
+    let bestFitData = fit(this.points, timeValues || this.mode),
+        x = bestFitData.C.x,
+        y = bestFitData.C.y,
+        bpoints = [];
+    x.forEach((r,i) => {
+      bpoints.push({
+        x: r[0],
+        y: y[i][0]
+      });
+    });
+    var curve = new api.Bezier(bpoints);
+    api.setCurve(curve);
+    this.curveset = true;
+    this.sliders.setOptions(bestFitData.S);
+    return curve;
+  },
+
+  onClick: function(evt, api) {
+    this.curveset = false;
+    this.points.push({x: api.mx, y: api.my });
+    api.redraw();
+  }
+};