Adds basic sprite sheet support to sprites

sky/examples/game/lib/sprite.dart

Index: sky/examples/game/lib/sprite.dart
diff --git a/sky/examples/game/lib/sprite.dart b/sky/examples/game/lib/sprite.dart
index a58168f18ee5977a8d771b62238251828a534ab0..24b482b35a6d58cfe73cc5065bee5d47abdb6be3 100644
--- a/sky/examples/game/lib/sprite.dart
+++ b/sky/examples/game/lib/sprite.dart
@@ -3,13 +3,13 @@ part of sprites;
 /// A Sprite is a [Node] that renders a bitmap image to the screen.
 class Sprite extends NodeWithSize {
 
-  /// The image that the sprite will render to screen.
+  /// The texture that the sprite will render to screen.
   ///
-  /// If the image is null, the sprite will be rendered as a red square
+  /// If the texture is null, the sprite will be rendered as a red square
   /// marking the bounds of the sprite.
   ///
-  ///     mySprite.image = myImage;
-  Image image;
+  ///     mySprite.texture = myTexture;
+  Texture texture;
 
   /// If true, constrains the proportions of the image by scaling it down, if its proportions doesn't match the [size].
   ///
@@ -29,14 +29,29 @@ class Sprite extends NodeWithSize {
   ///     mySprite.transferMode = TransferMode.plusMode;
   TransferMode transferMode;
 
+  /// Creates a new sprite from the provided [texture].
+  ///
+  ///     var mySprite = new Sprite(myTexture)
+  Sprite([this.texture]) {
+    if (texture != null) {
+      size = texture.size;
+      pivot = texture._pivot;
+    }
+    else {

[jackson, 2015/06/23 21:56:54]

I would move this onto the previous line

+      pivot = new Point(0.5, 0.5);
+    }
+  }
+
   /// Creates a new sprite from the provided [image].
   ///
-  /// var mySprite = new Sprite(myImage);
-  Sprite([Image this.image]) {
+  /// var mySprite = new Sprite.fromImage(myImage);
+  Sprite.fromImage(Image image) {
+    assert(image != null);
+
+    texture = new Texture(image);
+    size = texture.size;
+
     pivot = new Point(0.5, 0.5);
-    if (image != null) {
-      size = new Size(image.width.toDouble(), image.height.toDouble());
-    }
   }
 
   /// The opacity of the sprite in the range 0.0 to 1.0.
@@ -56,19 +71,23 @@ class Sprite extends NodeWithSize {
     // Account for pivot point
     applyTransformForPivot(canvas);
 
-    if (image != null && image.width > 0 && image.height > 0) {
+    if (texture != null) {
+      double w = texture.size.width;
+      double h = texture.size.height;
+
+      if (w <= 0 || h <= 0) return;

[jackson, 2015/06/23 21:56:54]

I would move return into the next line

       
-      double scaleX = size.width/image.width;
-      double scaleY = size.height/image.height;
+      double scaleX = size.width/w;

[jackson, 2015/06/23 21:56:54]

I would put a space around binary operators like /
https://www.dartlang.org/articles/style-guide/

+      double scaleY = size.height/h;

[jackson, 2015/06/23 21:56:54]

ditto

       
       if (constrainProportions) {
         // Constrain proportions, using the smallest scale and by centering the image
         if (scaleX < scaleY) {
-          canvas.translate(0.0, (size.height - scaleX * image.height)/2.0);
+          canvas.translate(0.0, (size.height - scaleX * h)/2.0);

[jackson, 2015/06/23 21:56:54]

ditto

           scaleY = scaleX;
         }
         else {
-          canvas.translate((size.width - scaleY * image.width)/2.0, 0.0);
+          canvas.translate((size.width - scaleY * w)/2.0, 0.0);

[jackson, 2015/06/23 21:56:54]

ditto

           scaleX = scaleY;
         }
       }
@@ -85,7 +104,8 @@ class Sprite extends NodeWithSize {
         paint.setTransferMode(transferMode);
       }
 
-      canvas.drawImage(image, 0.0, 0.0, paint);
+      // Do actual drawing of the sprite
+      canvas.drawImageRect(texture.image, texture._frame, texture._spriteSourceSize /*new Rect.fromLTRB(0.0, 0.0, w, h)*/, paint);

[jackson, 2015/06/23 21:56:54]

Did you mean to leave this comment in here? We don't usually use /**/ style
comments

     }
     else {
       // Paint a red square for missing texture