Merge pull request #1136 from abarth/optimize_scaffold

Optimize repainting in Scaffold

packages/flutter/lib/src/material/scaffold.dart

@@ -39,17 +39,17 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     // in this case the toolbar appears -after- the body in the stacking order,
     // so the toolbar's shadow is drawn on top of the body.
 
-    final BoxConstraints toolBarConstraints = looseConstraints.tightenWidth(size.width);
+    final BoxConstraints fullWidthConstraints = looseConstraints.tightenWidth(size.width);
     Size toolBarSize = Size.zero;
 
     if (isChild(_Child.toolBar)) {
-      toolBarSize = layoutChild(_Child.toolBar, toolBarConstraints);
+      toolBarSize = layoutChild(_Child.toolBar, fullWidthConstraints);
       positionChild(_Child.toolBar, Offset.zero);
     }
 
     if (isChild(_Child.body)) {
       final double bodyHeight = size.height - toolBarSize.height;
-      final BoxConstraints bodyConstraints = toolBarConstraints.tightenHeight(bodyHeight);
+      final BoxConstraints bodyConstraints = fullWidthConstraints.tightenHeight(bodyHeight);
       layoutChild(_Child.body, bodyConstraints);
       positionChild(_Child.body, new Offset(0.0, toolBarSize.height));
     }
@@ -63,7 +63,6 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     // non-zero height then it's inset from the parent's right and bottom edges
     // by _kFloatingActionButtonMargin.
 
-    final BoxConstraints fullWidthConstraints = looseConstraints.tightenWidth(size.width);
     Size bottomSheetSize = Size.zero;
     Size snackBarSize = Size.zero;
 
@@ -89,10 +88,12 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
     }
 
     if (isChild(_Child.drawer)) {
-      layoutChild(_Child.drawer, looseConstraints);
+      layoutChild(_Child.drawer, new BoxConstraints.tight(size));
       positionChild(_Child.drawer, Offset.zero);
     }
   }
+
+  bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => false;
 }
 
 class Scaffold extends StatefulComponent {

packages/flutter/lib/src/rendering/custom_layout.dart

@@ -92,7 +92,7 @@ abstract class MultiChildLayoutDelegate {
   }
 
   /// Override this method to return true when the children need to be laid out.
-  bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
+  bool shouldRelayout(MultiChildLayoutDelegate oldDelegate);
 
   /// Layout and position all children given this widget's size and the specified
   /// constraints. This method must apply layoutChild() to each child. It should

packages/flutter/lib/src/rendering/debug.dart

@@ -52,6 +52,12 @@ HSVColor debugCurrentRepaintColor = const HSVColor.fromAHSV(0.4, 60.0, 1.0, 1.0)
 /// The amount to increment the hue of the current repaint color.
 double debugRepaintRainboxHueIncrement = 2.0;
 
+/// Log the call stacks that mark render objects as needing paint.
+bool debugPrintMarkNeedsPaintStacks = false;
+
+/// Log the call stacks that mark render objects as needing layout.
+bool debugPrintMarkNeedsLayoutStacks = false;
+
 List<String> debugDescribeTransform(Matrix4 transform) {
   List<String> matrix = transform.toString().split('\n').map((String s) => '  $s').toList();
   matrix.removeLast();

packages/flutter/lib/src/rendering/object.dart

@@ -8,6 +8,7 @@ import 'dart:ui' as ui;
 
 import 'package:flutter/gestures.dart';
 import 'package:flutter/scheduler.dart';
+import 'package:flutter/services.dart';
 import 'package:vector_math/vector_math_64.dart';
 
 import 'debug.dart';
@@ -556,6 +557,11 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
       }
       assert(parent == this.parent);
     } else {
+      assert(() {
+        if (debugPrintMarkNeedsLayoutStacks)
+          debugPrintStack();
+        return true;
+      });
       _nodesNeedingLayout.add(this);
       Scheduler.instance.ensureVisualUpdate();
     }
@@ -950,6 +956,11 @@ abstract class RenderObject extends AbstractNode implements HitTestTarget {
       return;
     _needsPaint = true;
     if (hasLayer) {
+      assert(() {
+        if (debugPrintMarkNeedsPaintStacks)
+          debugPrintStack();
+        return true;
+      });
       // If we always have our own layer, then we can just repaint
       // ourselves without involving any other nodes.
       assert(_layer != null);

packages/flutter/lib/src/services/print.dart

@@ -44,3 +44,11 @@ void _debugPrintTask() {
     _debugPrintStopwatch.start();
   }
 }
+
+void debugPrintStack() {
+  try {
+    throw new Exception();
+  } catch (e, stack) {
+    debugPrint(stack.toString());
+  }
+}