rewrite to handler.js format

components/sections/arclengthapprox/handler.js

@@ -0,0 +1,58 @@
+module.exports = {
+  statics: {
+    keyHandlingOptions: {
+      propName: "steps",
+      values: {
+        "38": 1,  // up arrow
+        "40": -1 // down arrow
+      },
+      controller: function(api) {
+        if (api.steps < 1) {
+          api.steps = 1;
+        }
+      }
+    }
+  },
+
+  setupQuadratic: function(api) {
+    var curve = api.getDefaultQuadratic();
+    api.setCurve(curve);
+    api.steps = 10;
+  },
+
+  setupCubic: function(api) {
+    var curve = api.getDefaultCubic();
+    api.setCurve(curve);
+    api.steps = 16;
+  },
+
+  draw: function(api, curve) {
+    api.reset();
+    api.drawSkeleton(curve);
+
+    var pts = curve.getLUT(api.steps);
+
+    var step = 1 / api.steps;
+    var p0 = curve.points[0], pc;
+    for(var t=step; t<1.0+step; t+=step) {
+      pc = curve.get(Math.min(t,1));
+      api.setColor("red");
+      api.drawLine(p0,pc);
+      p0 = pc;
+    }
+
+    var len = curve.length();
+    var alen = 0;
+    for(var i=0,p1,dx,dy; i<pts.length-1; i++) {
+      p0 = pts[i];
+      p1 = pts[i+1];
+      dx = p1.x-p0.x;
+      dy = p1.y-p0.y;
+      alen += Math.sqrt(dx*dx+dy*dy);
+    }
+    alen = ((100*alen)|0)/100;
+    len = ((100*len)|0)/100;
+
+    api.text("Approximate length, "+api.steps+" steps: "+alen+" (true: "+len+")", {x:10, y: 15});
+  }
+};