// Copyright 2018 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. import 'package:flutter/widgets.dart'; import 'colors.dart'; /// Used with [TabBar.indicator] to draw a horizontal line below the /// selected tab. /// /// The selected tab underline is inset from the tab's boundary by [insets]. /// The [borderSide] defines the line's color and weight. /// /// The [TabBar.indicatorSize] property can be used to define the indicator's /// bounds in terms of its (centered) widget with [TabIndicatorSize.label], /// or the entire tab with [TabIndicatorSize.tab]. class UnderlineTabIndicator extends Decoration { /// Create an underline style selected tab indicator. /// /// The [borderSide] and [insets] arguments must not be null. const UnderlineTabIndicator({ this.borderSide = const BorderSide(width: 2.0, color: Colors.white), this.insets = EdgeInsets.zero, }) : assert(borderSide != null), assert(insets != null); /// The color and weight of the horizontal line drawn below the selected tab. final BorderSide borderSide; /// Locates the selected tab's underline relative to the tab's boundary. /// /// The [TabBar.indicatorSize] property can be used to define the /// tab indicator's bounds in terms of its (centered) tab widget with /// [TabIndicatorSize.label], or the entire tab with [TabIndicatorSize.tab]. final EdgeInsetsGeometry insets; @override Decoration lerpFrom(Decoration a, double t) { if (a is UnderlineTabIndicator) { return UnderlineTabIndicator( borderSide: BorderSide.lerp(a.borderSide, borderSide, t), insets: EdgeInsetsGeometry.lerp(a.insets, insets, t), ); } return super.lerpFrom(a, t); } @override Decoration lerpTo(Decoration b, double t) { if (b is UnderlineTabIndicator) { return UnderlineTabIndicator( borderSide: BorderSide.lerp(borderSide, b.borderSide, t), insets: EdgeInsetsGeometry.lerp(insets, b.insets, t), ); } return super.lerpTo(b, t); } @override _UnderlinePainter createBoxPainter([VoidCallback onChanged]) { return _UnderlinePainter(this, onChanged); } } class _UnderlinePainter extends BoxPainter { _UnderlinePainter(this.decoration, VoidCallback onChanged) : assert(decoration != null), super(onChanged); final UnderlineTabIndicator decoration; BorderSide get borderSide => decoration.borderSide; EdgeInsetsGeometry get insets => decoration.insets; Rect _indicatorRectFor(Rect rect, TextDirection textDirection) { assert(rect != null); assert(textDirection != null); final Rect indicator = insets.resolve(textDirection).deflateRect(rect); return Rect.fromLTWH( indicator.left, indicator.bottom - borderSide.width, indicator.width, borderSide.width, ); } @override void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) { assert(configuration != null); assert(configuration.size != null); final Rect rect = offset & configuration.size; final TextDirection textDirection = configuration.textDirection; final Rect indicator = _indicatorRectFor(rect, textDirection).deflate(borderSide.width / 2.0); final Paint paint = borderSide.toPaint()..strokeCap = StrokeCap.square; canvas.drawLine(indicator.bottomLeft, indicator.bottomRight, paint); } }