Allow for setting a start angle offset and an inner radius.

Readme.md

@@ -40,6 +40,26 @@
 
   Set the diameter to `n`.
 
+### Pie#angleOffset(angleOffset)
+
+  Set the start angle offset to `angleOffset`. This allows you to start the pie drawing at a position of your choosing. For instance, to start the pie drawing from 12 o'clock (as opposed to the default, 3 o'clock), you could:
+
+```javascript
+    pie.angleOffset( -Math.PI / 2 ); // add -90 degress to the default start angle of 3 o'clock 
+```
+
+### Pie#innerRadius(r)
+
+  Set the inner radius to `r`, allowing you to draw 'donut' style pie graphs. Eg:
+
+```javascript
+    pie.innerRadius( 10 ); // set a 10px inner radius
+```
+
+  Example image:
+
+  ![Inner Radius Example](example_images/inner_radius.png?raw=true)
+
 ### Pie#draw(ctx)
 
   Draw on `ctx`.

index.js

@@ -28,6 +28,8 @@ function Pie(selector) {
   this.borderColor = style(selector, 'border-color');
   this.color = style(selector, 'color');
   this.size(16);
+  this.angleOffset(0);
+  this.innerRadius(0);
 }
 
 /**
@@ -56,6 +58,30 @@ Pie.prototype.size = function(n){
   return this;
 };
 
+/**
+ * Set the start angle offset to 'angleOffset' in *radians*.
+ *
+ * @param {Number} angleOffset
+ * @return {Pie}
+ * @api public
+ */
+Pie.prototype.angleOffset = function(angleOffset) {
+  this._angleOffset = angleOffset;
+  return this;
+};
+
+/**
+ * Set the inner radius to 'r', drawing a 'donut' shaped pie graph.
+ *
+ * @param {Number} r
+ * @return {Pie}
+ * @api public
+ */
+Pie.prototype.innerRadius = function(r) {
+  this._innerRadius = r;
+  return this;
+};
+
 /**
  * Draw on to `ctx`.
  *
@@ -89,10 +115,21 @@ Pie.prototype.draw = function(ctx){
 
   // pie
   ctx.beginPath();
-  ctx.moveTo(half, half);
-  ctx.arc(half, half, half - this.borderWidth, 0, pi * n, false);
-  ctx.fillStyle = this.color;
-  ctx.fill();
+  if ( this._innerRadius > 0 )
+  {
+    var lineWidth = half - this.borderWidth - this._innerRadius;
+    ctx.arc(half, half, half - this.borderWidth - ( lineWidth / 2 ), 0 + this._angleOffset, ( pi * n ) + this._angleOffset, false);
+    ctx.lineWidth = lineWidth;
+    ctx.strokeStyle = this.color;
+    ctx.stroke();
+  }
+  else
+  {
+    ctx.moveTo(half,half);
+    ctx.arc(half, half, half - this.borderWidth, 0 + this._angleOffset, ( pi * n ) + this._angleOffset, false);
+    ctx.fillStyle = this.color;
+    ctx.fill();
+  }
 
   return this;
 };