decouple param validation from ellipse drawing

src/core/shape/2d_primitives.js

@@ -244,28 +244,7 @@ p5.prototype.arc = function(x, y, w, h, start, stop, mode, detail) {
 p5.prototype.ellipse = function(x, y, w, h, detailX) {
   p5._validateParameters('ellipse', arguments);
 
-  // if the current stroke and fill settings wouldn't result in something
-  // visible, exit immediately
-  if (!this._renderer._doStroke && !this._renderer._doFill) {
-    return this;
-  }
-
-  // p5 supports negative width and heights for rects
-  if (w < 0) {
-    w = Math.abs(w);
-  }
-
-  if (typeof h === 'undefined') {
-    // Duplicate 3rd argument if only 3 given.
-    h = w;
-  } else if (h < 0) {
-    h = Math.abs(h);
-  }
-
-  const vals = canvas.modeAdjust(x, y, w, h, this._renderer._ellipseMode);
-  this._renderer.ellipse([vals.x, vals.y, vals.w, vals.h, detailX]);
-
-  return this;
+  return this._renderEllipse(...arguments);
 };
 
 /**
@@ -292,10 +271,37 @@ p5.prototype.ellipse = function(x, y, w, h, detailX) {
  * white circle with black outline in mid of canvas that is 55x55.
  */
 p5.prototype.circle = function() {
+  p5._validateParameters('circle', arguments);
   const args = Array.prototype.slice.call(arguments, 0, 2);
   args.push(arguments[2]);
   args.push(arguments[2]);
-  return this.ellipse(...args);
+  return this._renderEllipse(...args);
+};
+
+// internal method for drawing ellipses (without parameter validation)
+p5.prototype._renderEllipse = function(x, y, w, h, detailX) {
+  // if the current stroke and fill settings wouldn't result in something
+  // visible, exit immediately
+  if (!this._renderer._doStroke && !this._renderer._doFill) {
+    return this;
+  }
+
+  // p5 supports negative width and heights for rects
+  if (w < 0) {
+    w = Math.abs(w);
+  }
+
+  if (typeof h === 'undefined') {
+    // Duplicate 3rd argument if only 3 given.
+    h = w;
+  } else if (h < 0) {
+    h = Math.abs(h);
+  }
+
+  const vals = canvas.modeAdjust(x, y, w, h, this._renderer._ellipseMode);
+  this._renderer.ellipse([vals.x, vals.y, vals.w, vals.h, detailX]);
+
+  return this;
 };
 
 /**