Fix Path#arcTo() when from/to points are equal

Closes #1613

CHANGELOG.md

@@ -13,6 +13,7 @@
 - Do not ignore `Group#clipItem.matrix` in `Group#internalBounds` (#1427).
 - Correctly calculate bounds with nested empty items (#1467).
 - Fix color change propagation on groups (#1152).
+- Fix `Path#arcTo()` where `from` and `to` points are equal (#1613).
 - SVG Export: Fix error when `Item#matrix` is not invertible (#1580).
 - SVG Export: Include missing viewBox attribute (#1576).
 - SVG Import: Use correct default values for gradients (#1632, #1661).

src/path/Path.js

@@ -2467,9 +2467,10 @@ new function() { // PostScript-style drawing commands
                 // #2: arcTo(through, to)
                 through = to;
                 to = Point.read(arguments);
-            } else {
+            } else if (!from.equals(to)) {
                 // #3: arcTo(to, radius, rotation, clockwise, large)
-                // Drawing arcs in SVG style:
+                // Draw arc in SVG style, but only if `from` and `to` are not
+                // equal (#1613).
                 var radius = Size.read(arguments),
                     isZero = Numerical.isZero;
                 // If rx = 0 or ry = 0 then this arc is treated as a
@@ -2565,11 +2566,12 @@ new function() { // PostScript-style drawing commands
                     extent += extent < 0 ? 360 : -360;
                 }
             }
+            if (extent) {
                 var epsilon = /*#=*/Numerical.GEOMETRIC_EPSILON,
                     ext = abs(extent),
-                // Calculate the amount of segments required to approximate over
+                    // Calculate amount of segments required to approximate over
                     // `extend` degrees (extend / 90), but prevent ceil() from
-                // rounding up small imprecisions by subtracting epsilon first.
+                    // rounding up small imprecisions by subtracting epsilon.
                     count = ext >= 360 ? 4 : Math.ceil((ext - epsilon) / 90),
                     inc = extent / count,
                     half = inc * Math.PI / 360,
@@ -2606,6 +2608,7 @@ new function() { // PostScript-style drawing commands
                 }
                 // Add all segments at once at the end for higher performance
                 this._add(segments);
+            }
         },
 
         lineBy: function(/* to */) {

test/tests/Path.js

@@ -645,3 +645,11 @@ test('Path#arcTo(through, to) is on through point side (#1477)', function() {
     path.arcTo(p2, p3);
     equals(true, path.segments[1].point.x > p1.x);
 });
+
+test('Path#arcTo(to, radius, rotation, clockwise, large) when from and to are equal (#1613)', function(){
+    var point = new Point(10,10);
+    var path = new Path();
+    path.moveTo(point);
+    path.arcTo(point, new Size(10), 0, true, true);
+    expect(0);
+});