Add support for TextOverflow.ellipsis (#3818)

Fixes #417

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

@@ -209,7 +209,13 @@ class AppBar extends StatelessWidget {
     toolBarRow.add(new Flexible(
       child: new Padding(
         padding: new EdgeInsets.only(left: 8.0),
-        child: title != null ? new DefaultTextStyle(style: centerStyle, child: title) : null
+        child: title != null ?
+          new DefaultTextStyle(
+            style: centerStyle,
+            softWrap: false,
+            overflow: TextOverflow.ellipsis,
+            child: title
+          ) : null
       )
     ));
     if (actions != null)

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

@@ -345,7 +345,12 @@ class _Tab extends StatelessWidget {
   Widget _buildLabelText() {
     assert(label.text != null);
     TextStyle style = new TextStyle(color: color);
-    return new Text(label.text, style: style);
+    return new Text(
+      label.text,
+      style: style,
+      softWrap: false,
+      overflow: TextOverflow.fade
+    );
   }
 
   Widget _buildLabelIcon(BuildContext context) {
@@ -371,15 +376,15 @@ class _Tab extends StatelessWidget {
       labelContent = _buildLabelIcon(context);
     } else {
       labelContent = new Column(
+        mainAxisAlignment: MainAxisAlignment.center,
+        crossAxisAlignment: CrossAxisAlignment.center,
         children: <Widget>[
           new Container(
             child: _buildLabelIcon(context),
             margin: const EdgeInsets.only(bottom: 10.0)
           ),
           _buildLabelText()
-        ],
-        mainAxisAlignment: MainAxisAlignment.center,
-        crossAxisAlignment: CrossAxisAlignment.center
+        ]
       );
     }
 

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

@@ -2,20 +2,42 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui' as ui;
+
 import 'package:flutter/gestures.dart';
 
 import 'box.dart';
 import 'object.dart';
 import 'semantics.dart';
 
+/// How overflowing text should be handled.
+enum TextOverflow {
+  /// Clip the overflowing text to fix its container.
+  clip,
+
+  /// Fade the overflowing text to transparent.
+  fade,
+
+  /// Use an ellipsis to indicate that the text has overflowed.
+  ellipsis,
+}
+
 /// A render object that displays a paragraph of text
 class RenderParagraph extends RenderBox {
-
+  /// Creates a paragraph render object.
+  ///
+  /// The [text], [overflow], and [softWrap] arguments must not be null.
   RenderParagraph(TextSpan text, {
-    TextAlign textAlign
-  }) : _textPainter = new TextPainter(text: text, textAlign: textAlign) {
+    TextAlign textAlign,
+    TextOverflow overflow: TextOverflow.clip,
+    bool softWrap: true
+  }) : _softWrap = softWrap,
+       _overflow = overflow,
+       _textPainter = new TextPainter(text: text, textAlign: textAlign) {
     assert(text != null);
     assert(text.debugAssertValid());
+    assert(overflow != null);
+    assert(softWrap != null);
   }
 
   final TextPainter _textPainter;
@@ -27,6 +49,8 @@ class RenderParagraph extends RenderBox {
     if (_textPainter.text == value)
       return;
     _textPainter.text = value;
+    _overflowPainter = null;
+    _overflowShader = null;
     markNeedsLayout();
   }
 
@@ -39,10 +63,34 @@ class RenderParagraph extends RenderBox {
     markNeedsPaint();
   }
 
+  /// Whether the text should break at soft line breaks.
+  ///
+  /// If false, the glyphs in the text will be positioned as if there was unlimited horizontal space.
+  bool get softWrap => _softWrap;
+  bool _softWrap;
+  void set softWrap(bool value) {
+    assert(value != null);
+    if (_softWrap == value)
+      return;
+    _softWrap = value;
+    markNeedsLayout();
+  }
+
+  /// How visual overflow should be handled.
+  TextOverflow get overflow => _overflow;
+  TextOverflow _overflow;
+  void set overflow(TextOverflow value) {
+    assert(value != null);
+    if (_overflow == value)
+      return;
+    _overflow = value;
+    markNeedsPaint();
+  }
+
   void _layoutText(BoxConstraints constraints) {
     assert(constraints != null);
     assert(constraints.debugAssertIsValid());
-    _textPainter.layout(minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
+    _textPainter.layout(minWidth: constraints.minWidth, maxWidth: _softWrap ? constraints.maxWidth : double.INFINITY);
   }
 
   @override
@@ -95,10 +143,49 @@ class RenderParagraph extends RenderBox {
     span?.recognizer?.addPointer(event);
   }
 
+  bool _hasVisualOverflow = false;
+  TextPainter _overflowPainter;
+  ui.Shader _overflowShader;
+
   @override
   void performLayout() {
     _layoutText(constraints);
     size = constraints.constrain(_textPainter.size);
+
+    final bool didOverflowWidth = size.width < _textPainter.width;
+    // TODO(abarth): We're only measuring the sizes of the line boxes here. If
+    // the glyphs draw outside the line boxes, we might think that there isn't
+    // visual overflow when there actually is visual overflow. This can become
+    // a problem if we start having horizontal overflow and introduce a clip
+    // that affects the actual (but undetected) vertical overflow.
+    _hasVisualOverflow = didOverflowWidth || size.height < _textPainter.height;
+    if (didOverflowWidth) {
+      switch (_overflow) {
+        case TextOverflow.clip:
+          _overflowPainter = null;
+          _overflowShader = null;
+          break;
+        case TextOverflow.fade:
+        case TextOverflow.ellipsis:
+          _overflowPainter ??= new TextPainter(
+            text: new TextSpan(style: _textPainter.text.style, text: '\u2026')
+          )..layout();
+          final double overflowUnit = _overflowPainter.width;
+          double fadeEnd = size.width;
+          if (_overflow == TextOverflow.ellipsis)
+            fadeEnd -= overflowUnit / 2.0;
+          final double fadeStart = fadeEnd - _overflowPainter.width;
+          // TODO(abarth): This shader has an LTR bias.
+          _overflowShader = new ui.Gradient.linear(
+            <Point>[new Point(fadeStart, 0.0), new Point(fadeEnd, 0.0)],
+            <Color>[const Color(0xFFFFFFFF), const Color(0x00FFFFFF)]
+          );
+          break;
+      }
+    } else {
+      _overflowPainter = null;
+      _overflowShader = null;
+    }
   }
 
   @override
@@ -114,7 +201,31 @@ class RenderParagraph extends RenderBox {
     // If you remove this call, make sure that changing the textAlign still
     // works properly.
     _layoutText(constraints);
-    _textPainter.paint(context.canvas, offset);
+    final Canvas canvas = context.canvas;
+    if (_hasVisualOverflow) {
+      final Rect bounds = offset & size;
+      if (_overflowPainter != null)
+        canvas.saveLayer(bounds, new Paint());
+      else
+        canvas.save();
+      canvas.clipRect(bounds);
+    }
+    _textPainter.paint(canvas, offset);
+    if (_hasVisualOverflow) {
+      if (_overflowShader != null) {
+        canvas.translate(offset.dx, offset.dy);
+        Paint paint = new Paint()
+          ..transferMode = TransferMode.modulate
+          ..shader = _overflowShader;
+        canvas.drawRect(Point.origin & size, paint);
+        if (_overflow == TextOverflow.ellipsis) {
+          // TODO(abarth): This paint offset has an LTR bias.
+          Offset ellipseOffset = new Offset(size.width - _overflowPainter.width, 0.0);
+          _overflowPainter.paint(canvas, ellipseOffset);
+        }
+      }
+      canvas.restore();
+    }
   }
 
   @override

packages/flutter/lib/src/widgets/basic.dart

@@ -45,6 +45,7 @@ export 'package:flutter/rendering.dart' show
     RenderObjectPainter,
     ShaderCallback,
     SingleChildLayoutDelegate,
+    TextOverflow,
     ValueChanged,
     ViewportAnchor,
     ViewportDimensions,
@@ -1904,8 +1905,16 @@ class RichText extends LeafRenderObjectWidget {
   /// Creates a paragraph of rich text.
   ///
   /// The [text] argument is required to be non-null.
-  RichText({ Key key, this.text, this.textAlign }) : super(key: key) {
+  RichText({
+    Key key,
+    this.text,
+    this.textAlign,
+    this.softWrap: true,
+    this.overflow: TextOverflow.clip
+  }) : super(key: key) {
     assert(text != null);
+    assert(softWrap != null);
+    assert(overflow != null);
   }
 
   /// The text to display in this widget.
@@ -1914,16 +1923,30 @@ class RichText extends LeafRenderObjectWidget {
   /// How the text should be aligned horizontally.
   final TextAlign textAlign;
 
+  /// Whether the text should break at soft line breaks.
+  ///
+  /// If false, the glyphs in the text will be positioned as if there was unlimited horizontal space.
+  final bool softWrap;
+
+  /// How visual overflow should be handled.
+  final TextOverflow overflow;
+
   @override
   RenderParagraph createRenderObject(BuildContext context) {
-    return new RenderParagraph(text, textAlign: textAlign);
+    return new RenderParagraph(text,
+      textAlign: textAlign,
+      softWrap: softWrap,
+      overflow: overflow
+    );
   }
 
   @override
   void updateRenderObject(BuildContext context, RenderParagraph renderObject) {
     renderObject
       ..text = text
-      ..textAlign = textAlign;
+      ..textAlign = textAlign
+      ..softWrap = softWrap
+      ..overflow = overflow;
   }
 }
 
@@ -1937,16 +1960,24 @@ class DefaultTextStyle extends InheritedWidget {
     Key key,
     this.style,
     this.textAlign,
+    this.softWrap: true,
+    this.overflow: TextOverflow.clip,
     Widget child
   }) : super(key: key, child: child) {
     assert(style != null);
+    assert(softWrap != null);
+    assert(overflow != null);
     assert(child != null);
   }
 
   /// A const-constructible default text style that provides fallback values.
   ///
   /// Returned from [of] when the given [BuildContext] doesn't have an enclosing default text style.
-  const DefaultTextStyle.fallback() : style = const TextStyle(), textAlign = null;
+  const DefaultTextStyle.fallback()
+    : style = const TextStyle(),
+      textAlign = null,
+      softWrap = true,
+      overflow = TextOverflow.clip;
 
   /// Creates a default text style that inherits from the given [BuildContext].
   ///
@@ -1959,6 +1990,8 @@ class DefaultTextStyle extends InheritedWidget {
     BuildContext context,
     TextStyle style,
     TextAlign textAlign,
+    bool softWrap,
+    TextOverflow overflow,
     Widget child
   }) {
     DefaultTextStyle parent = DefaultTextStyle.of(context);
@@ -1966,6 +1999,8 @@ class DefaultTextStyle extends InheritedWidget {
       key: key,
       style: parent.style.merge(style),
       textAlign: textAlign ?? parent.textAlign,
+      softWrap: softWrap ?? parent.softWrap,
+      overflow: overflow ?? parent.overflow,
       child: child
     );
   }
@@ -1976,6 +2011,14 @@ class DefaultTextStyle extends InheritedWidget {
   /// How the text should be aligned horizontally.
   final TextAlign textAlign;
 
+  /// Whether the text should break at soft line breaks.
+  ///
+  /// If false, the glyphs in the text will be positioned as if there was unlimited horizontal space.
+  final bool softWrap;
+
+  /// How visual overflow should be handled.
+  final TextOverflow overflow;
+
   /// The closest instance of this class that encloses the given context.
   ///
   /// If no such instance exists, returns an instance created by
@@ -2019,7 +2062,13 @@ class Text extends StatelessWidget {
   ///
   /// If the [style] argument is null, the text will use the style from the
   /// closest enclosing [DefaultTextStyle].
-  Text(this.data, { Key key, this.style, this.textAlign }) : super(key: key) {
+  Text(this.data, {
+    Key key,
+    this.style,
+    this.textAlign,
+    this.softWrap,
+    this.overflow
+  }) : super(key: key) {
     assert(data != null);
   }
 
@@ -2036,21 +2085,24 @@ class Text extends StatelessWidget {
   /// How the text should be aligned horizontally.
   final TextAlign textAlign;
 
+  /// Whether the text should break at soft line breaks.
+  ///
+  /// If false, the glyphs in the text will be positioned as if there was unlimited horizontal space.
+  final bool softWrap;
+
+  /// How visual overflow should be handled.
+  final TextOverflow overflow;
+
   @override
   Widget build(BuildContext context) {
-    DefaultTextStyle defaultTextStyle;
+    DefaultTextStyle defaultTextStyle = DefaultTextStyle.of(context);
     TextStyle effectiveTextStyle = style;
-    if (style == null || style.inherit) {
-      defaultTextStyle ??= DefaultTextStyle.of(context);
+    if (style == null || style.inherit)
       effectiveTextStyle = defaultTextStyle.style.merge(style);
-    }
-    TextAlign effectiveTextAlign = textAlign;
-    if (effectiveTextAlign == null) {
-      defaultTextStyle ??= DefaultTextStyle.of(context);
-      effectiveTextAlign = defaultTextStyle.textAlign;
-    }
     return new RichText(
-      textAlign: effectiveTextAlign,
+      textAlign: textAlign ?? defaultTextStyle.textAlign,
+      softWrap: softWrap ?? defaultTextStyle.softWrap,
+      overflow: overflow ?? defaultTextStyle.overflow,
       text: new TextSpan(
         style: effectiveTextStyle,
         text: data