unarc: don't drop degenerated arcs, #20

lib/svgpath.js

@@ -496,13 +496,14 @@ SvgPath.prototype.unarc = function () {
       nextY = s[7];
     }
 
-    // one of the radii is zero, treating it as a line segment instead
-    if (s[1] === 0 || s[2] === 0) {
+    new_segments = a2c(x, y, nextX, nextY, s[4], s[5], s[1], s[2], s[3]);
+
+    // Degenerated arcs can be ignored by renderer, but should not be dropped
+    // to avoid collisions wish `S A S` and so on. Replace with empty line.
+    if (new_segments.length === 0) {
       return [ [ 'L', nextX, nextY ] ];
     }
 
-    new_segments = a2c(x, y, nextX, nextY, s[4], s[5], s[1], s[2], s[3]);
-
     new_segments.forEach(function (s) {
       result.push([ 'C', s[2], s[3], s[4], s[5], s[6], s[7] ]);
     });

test/api.js

@@ -490,7 +490,7 @@ describe('API', function () {
       //
       assert.equal(
         svgpath('M100 100A123 456 90 0 1 100 100').unarc().round(0).toString(),
-        'M100 100'
+        'M100 100L100 100'
       );
     });