Improved documentation for SkyGames and support for rotated textures

sky/examples/game/lib/spritesheet.dart

Index: sky/examples/game/lib/spritesheet.dart
diff --git a/sky/examples/game/lib/spritesheet.dart b/sky/examples/game/lib/spritesheet.dart
index 57d84883fe229d1ae4b8625e8a991685b920fd46..39bf503a28808d2883d9e8c3a096ab9b6996aad6 100644
--- a/sky/examples/game/lib/spritesheet.dart
+++ b/sky/examples/game/lib/spritesheet.dart
@@ -1,10 +1,19 @@
 part of sprites;
 
+/// A sprite sheet packs a number of smaller images into a single large image.
+///
+/// The placement of the smaller images are defined by a json file. The larger image and json file is typically created
+/// by a tool such as TexturePacker. The [SpriteSheet] class will take a reference to a larger image and a json string.
+/// From the image and the string the [SpriteSheet] creates a number of [Texture] objects. The names of the frames in
+/// the sprite sheet definition are used to reference the different textures.
 class SpriteSheet {
 
   Image _image;
   Map<String, Texture> _textures = new Map();
 
+  /// Creates a new sprite sheet from an [_image] and a sprite sheet [jsonDefinition].
+  ///
+  ///     var mySpriteSheet = new SpriteSheet(myImage, jsonString);
   SpriteSheet(this._image, String jsonDefinition) {
     assert(_image != null);
     assert(jsonDefinition != null);
@@ -53,7 +62,13 @@ class SpriteSheet {
     return new Point(x.toDouble(), y.toDouble());
   }
 
+  /// The image used by the sprite sheet.
+  ///
+  ///     var spriteSheetImage = mySpriteSheet.image;
   Image get image => _image;
 
+  /// Returns a texture by its name.
+  ///
+  ///     var myTexture = mySpriteSheet["example.png"];
   Texture operator [](String fileName) => _textures[fileName];
 }