From 2e8e2d0b72896d771ab96bfe9339f5518ca4e6b8 Mon Sep 17 00:00:00 2001
From: Eric Seidel <eseidel@chromium.org>
Date: Wed, 8 Jul 2015 13:47:39 -0700
Subject: [PATCH] Make RenderBlock painting match its hittesting

I added a clip in RenderBlock to make the painted pixels
match the hittesting logic.  This at least makes obvious
all the numerous hittesting bugs in our system. :)

I also moved demo_launcher to ScrollableList awesomeness.

R=abarth@chromium.org, abarth@google.com

Review URL: https://codereview.chromium.org/1223083002 .
---
 sdk/example/demo_launcher/lib/main.dart | 20 +++++++++-----------
 sdk/lib/rendering/block.dart            | 14 ++++++++++++++
 2 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/sdk/example/demo_launcher/lib/main.dart b/sdk/example/demo_launcher/lib/main.dart
index 75c0f46fe1f..0ad0bb18163 100644
--- a/sdk/example/demo_launcher/lib/main.dart
+++ b/sdk/example/demo_launcher/lib/main.dart
@@ -19,6 +19,7 @@ import 'package:sky/widgets/scaffold.dart';
 import 'package:sky/widgets/task_description.dart';
 import 'package:sky/widgets/theme.dart';
 import 'package:sky/widgets/tool_bar.dart';
+import 'package:sky/widgets/scrollable_list.dart';
 
 AssetBundle _initBundle() {
   if (rootBundle != null)
@@ -132,11 +133,7 @@ List<Widget> demos = [
 const double kCardHeight = 120.0;
 const EdgeDims kListPadding = const EdgeDims.all(4.0);
 
-class DemoList extends FixedHeightScrollable {
-  DemoList({ String key }) : super(key: key, itemHeight: kCardHeight, padding: kListPadding);
-
-  int get itemCount => demos.length;
-
+class DemoList extends Component {
   Widget buildDemo(SkyDemo demo) {
     return new Listener(
       key: demo.name,
@@ -166,12 +163,13 @@ class DemoList extends FixedHeightScrollable {
     );
   }
 
-  List<Widget> buildItems(int start, int count) {
-    return demos
-      .skip(start)
-      .take(count)
-      .map(buildDemo)
-      .toList(growable: false);
+  Widget build() {
+    return new ScrollableList<SkyDemo>(
+      items: demos,
+      itemHeight: kCardHeight,
+      itemBuilder: buildDemo,
+      padding: kListPadding
+    );
   }
 }
 
diff --git a/sdk/lib/rendering/block.dart b/sdk/lib/rendering/block.dart
index 939e62ceaba..11f20ef30ab 100644
--- a/sdk/lib/rendering/block.dart
+++ b/sdk/lib/rendering/block.dart
@@ -15,6 +15,8 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
   // uses the maximum width provided by the parent
   // sizes itself to the height of its child stack
 
+  bool _hasVisualOverflow = false;
+
   RenderBlock({
     List<RenderBox> children
   }) {
@@ -94,7 +96,12 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
       y += child.size.height;
       child = child.parentData.nextSibling;
     }
+    // FIXME(eseidel): Block lays out its children with unconstrained height
+    // yet itself remains constrained. Remember that our children wanted to
+    // be taller than we are so we know to clip them (and not cause confusing
+    // mismatch of painting vs. hittesting).
     size = new Size(width, constraints.constrainHeight(y));
+    _hasVisualOverflow = y > size.height;
     assert(!size.isInfinite);
   }
 
@@ -103,7 +110,14 @@ class RenderBlock extends RenderBox with ContainerRenderObjectMixin<RenderBox, B
   }
 
   void paint(PaintingCanvas canvas, Offset offset) {
+    if (_hasVisualOverflow) {
+      canvas.save();
+      canvas.clipRect(offset & size);
+    }
     defaultPaint(canvas, offset);
+    if (_hasVisualOverflow) {
+      canvas.restore();
+    }
   }
 
 }