Fixes lineWidth/scale calculation for the fonts

src/canvas.js

@@ -799,7 +799,9 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
         this.applyTextTransforms();
 
         var lineWidth = current.lineWidth;
-        var scale = Math.abs(current.textMatrix[0] * fontMatrix[0]);
+        var a1 = current.textMatrix[0], b1 = current.textMatrix[1];
+        var a2 = fontMatrix[0], b2 = fontMatrix[1];
+        var scale = Math.sqrt((a1 * a1 + b1 * b1) * (a2 * a2 + b2 * b2));
         if (scale == 0 || lineWidth == 0)
           lineWidth = this.getSinglePixelWidth();
         else
@@ -1340,7 +1342,10 @@ var CanvasGraphics = (function CanvasGraphicsClosure() {
     },
     getSinglePixelWidth: function CanvasGraphics_getSinglePixelWidth(scale) {
       var inverse = this.ctx.mozCurrentTransformInverse;
-      return Math.abs(inverse[0] + inverse[2]);
+      // max of the current horizontal and vertical scale
+      return Math.sqrt(Math.max(
+        (inverse[0] * inverse[0] + inverse[1] * inverse[1]),
+        (inverse[2] * inverse[2] + inverse[3] * inverse[3])));
     }
   };