Implement RenderImage and Image for Sky

sky/sdk/lib/framework/rendering/box.dart

Index: sky/sdk/lib/framework/rendering/box.dart
diff --git a/sky/sdk/lib/framework/rendering/box.dart b/sky/sdk/lib/framework/rendering/box.dart
index 803c85b2b884b7e1d962cfa6940fd2f753dd3fc5..a79686b54bab58f0b9cba252da6870af67ddfbbf 100644
--- a/sky/sdk/lib/framework/rendering/box.dart
+++ b/sky/sdk/lib/framework/rendering/box.dart
@@ -4,6 +4,7 @@
 
 import 'node.dart';
 import 'dart:sky' as sky;
+import 'package:sky/framework/net/image_cache.dart' as image_cache;
 
 // GENERIC BOX RENDERING
 // Anything that has a concept of x, y, width, height is going to derive from this
@@ -243,6 +244,71 @@ class RenderPadding extends RenderBox with RenderNodeWithChildMixin<RenderBox> {
 
 }
 
+class RenderImage extends RenderBox {
+
+  RenderImage(String src, sky.Size dimensions) {
+    requestedSize = dimensions;
+    image_cache.load(src, (result) {
+      _image = result;
+      markNeedsLayout();
+      markNeedsPaint();
+    });
+  }
+
+  sky.Image _image;
+  sky.Size _requestedSize;
+  sky.Size get requestedSize => _requestedSize;
+  void set requestedSize (sky.Size value) {
+    if (value == _requestedSize)
+      return;
+    _requestedSize = value;
+    markNeedsLayout();
+    markNeedsPaint();

[abarth-chromium, 2015/06/03 17:53:21]

No need to call markNeedsPaint here.  markNeedsLayout will trigger a
markNeedsPaint automatically if something about the size ends up mattering.

[jackson, 2015/06/03 22:06:26]

Done.

+  }
+
+  void _updateSizeFromImage() {

[abarth-chromium, 2015/06/03 17:53:21]

This function has one caller, performLayout.  We should just inline it into that
one caller.

[jackson, 2015/06/03 22:06:26]

Done.

+    // If both height and width are specified, we don't care about image dimensions
+    if (requestedSize.width != null && requestedSize.height != null)
+      size = constraints.constrain(requestedSize);

[abarth-chromium, 2015/06/03 17:53:21]

Should we return in this case?

[jackson, 2015/06/03 22:06:26]

Done.

+
+    // If there's no image, we can't size ourselves
+    if (_image == null)
+      return;
+
+    // If neither height nor width are specified, use inherent image dimensions
+    // If only one dimension is specified, adjust the other dimension to
+    // maintain the aspect ratio
+    if (requestedSize.width == null) {
+      if (requestedSize.height == null) {
+        size = constraints.constrain(new sky.Size(_image.width, _image.height));
+      } else {
+        num width = requestedSize.height * _image.width / _image.height;

[abarth-chromium, 2015/06/03 17:53:21]

s/num/double/  It's always a double 

[jackson, 2015/06/03 22:06:26]

Done.

+        size = constraints.constrain(new sky.Size(width, requestedSize.height));
+      }
+    } else if (requestedSize.height == null) {
+      num height = requestedSize.width * _image.height / _image.width;
+      size = constraints.constrain(new sky.Size(requestedSize.width, height));
+    } else {
+      size = constraints.constrain(requestedSize);
+    }
+  }
+
+  void performLayout() {
+    _updateSizeFromImage();
+  }
+
+  void paint(RenderNodeDisplayList canvas) {
+    if (_image == null) return;
+    double widthScale = size.width / _image.width;
+    double heightScale = size.height / _image.height;
+    canvas.save();
+    canvas.scale(widthScale, heightScale);

[abarth-chromium, 2015/06/03 17:53:21]

We should skip the save/scale/restore dance if size.width == _image.width &&
size.height == _image.height.  Calling save/scale/restore is expensive and
unnecessary in the common case that the size of the RenderImage matches the
intrinsic dimensions of the underlying image object.

[jackson, 2015/06/03 22:06:26]

Done.

+    sky.Paint paint = new sky.Paint();
+    canvas.drawImage(_image, 0.0, 0.0, paint);
+    canvas.restore();
+  }
+}
+
 // This must be immutable, because we won't notice when it changes
 class BoxDecoration {
   // TODO(mpcomplete): go through and change the users of this class to pass