Sky: Small fixes to Gradient interface. Added comments and renamed constructors.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1180873003.

engine/core/painting/Gradient.dart

@@ -4,19 +4,26 @@
 
 part of dart.sky;
 
+/// Defines what happens at the edge of the gradient.
 enum TileMode {
+  /// Edge is clamped to the final color.
   clamp,
+  /// Edge is repeated from first color to last.
   repeated,
+  /// Edge is mirrored from last color to first.
   mirror
 }
 
-// Extends the generated _Gradient interface via the PrivateDart attribute.
+/// Extends the generated _Gradient interface via the PrivateDart attribute.
 class Gradient extends _Gradient {
+  /// Creates a linear gradient from [endPoint[0]] to [endPoint[1]]. If
+  /// [colorStops] is provided, [colorStops[i]] is a number from 0 to 1 that
+  /// specifies where [color[i]] begins in the gradient.
   // TODO(mpcomplete): Maybe pass a list of (color, colorStop) pairs instead?
-  Gradient.Linear(List<Point> endPoints,
+  Gradient.linear(List<Point> endPoints,
                   List<Color> colors,
-                  List<double> colorStops,
-                  [TileMode tileMode = TileMode.clamp])
+                  [List<double> colorStops = null,
+                  TileMode tileMode = TileMode.clamp])
       : super() {
     if (endPoints == null || endPoints.length != 2)
       throw new ArgumentError("Expected exactly 2 [endPoints].");
@@ -24,11 +31,15 @@ class Gradient extends _Gradient {
     this._initLinear(endPoints, colors, colorStops, tileMode);
   }
 
-  Gradient.Radial(Point center,
+  /// Creates a radial gradient centered at [center] that ends at [radius]
+  /// distance from the center. If [colorStops] is provided, [colorStops[i]] is
+  /// a number from 0 to 1 that specifies where [color[i]] begins in the
+  /// gradient.
+  Gradient.radial(Point center,
                   double radius,
                   List<Color> colors,
-                  List<double> colorStops,
-                  [TileMode tileMode = TileMode.clamp])
+                  [List<double> colorStops = null,
+                  TileMode tileMode = TileMode.clamp])
       : super() {
     validateColorStops(colors, colorStops);
     this._initRadial(center, radius, colors, colorStops, tileMode);

examples/raw/painting.sky

@@ -26,10 +26,9 @@ void main() {
     paint.color = const Color.fromARGB(128, 255, 0, 255);
     context.rotate(math.PI/4.0);
 
-    Gradient yellowBlue = new Gradient.Linear(
+    Gradient yellowBlue = new Gradient.linear(
         [new Point(-radius, -radius), new Point(0.0, 0.0)],
-        [const Color(0xFFFFFF00), const Color(0xFF0000FF)],
-        null);
+        [const Color(0xFFFFFF00), const Color(0xFF0000FF)]);
     context.drawRect(new Rect.fromLTRB(-radius, -radius, radius, radius),
                      new Paint()..setShader(yellowBlue));
 
@@ -67,7 +66,7 @@ void main() {
               ..setColorMode(TransferMode.srcMode)
               ..setPaintBits(-1),
             (Paint layerPaint) {
-          Gradient redYellow = new Gradient.Radial(
+          Gradient redYellow = new Gradient.radial(
               new Point(0.0, 0.0), radius/3.0,
               [const Color(0xFFFFFF00), const Color(0xFFFF0000)],
               null, TileMode.mirror);

sdk/lib/framework/painting/box_painter.dart

@@ -85,7 +85,7 @@ class LinearGradient extends Gradient {
       'LinearGradient($endPoints, $colors, $colorStops, $tileMode)';
 
   sky.Shader createShader() {
-    return new sky.Gradient.Linear(this.endPoints, this.colors, this.colorStops,
+    return new sky.Gradient.linear(this.endPoints, this.colors, this.colorStops,
                                    this.tileMode);
   }
 
@@ -108,7 +108,7 @@ class RadialGradient extends Gradient {
       'RadialGradient($center, $radius, $colors, $colorStops, $tileMode)';
 
   sky.Shader createShader() {
-    return new sky.Gradient.Radial(this.center, this.radius, this.colors,
+    return new sky.Gradient.radial(this.center, this.radius, this.colors,
                                    this.colorStops, this.tileMode);
   }