continuous_rectangle_border.dart

// Copyright 2014 The Flutter 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 'dart:math' as math;

import 'package:flutter/foundation.dart';

import 'basic_types.dart';
import 'border_radius.dart';
import 'borders.dart';
import 'edge_insets.dart';

/// A rectangular border with smooth continuous transitions between the straight
/// sides and the rounded corners.
///
/// {@tool snippet}
/// ```dart
/// Widget build(BuildContext context) {
///   return Material(
///     shape: ContinuousRectangleBorder(
///       borderRadius: BorderRadius.circular(28.0),
///     ),
///   );
/// }
/// ```
/// {@end-tool}
///
/// See also:
///
///  * [RoundedRectangleBorder] Which creates rectangles with rounded corners,
///    however its straight sides change into a rounded corner with a circular
///    radius in a step function instead of gradually like the
///    [ContinuousRectangleBorder].
class ContinuousRectangleBorder extends ShapeBorder {
  /// The arguments must not be null.
  const ContinuousRectangleBorder({
    this.side = BorderSide.none,
    this.borderRadius = BorderRadius.zero,
  }) : assert(side != null),
       assert(borderRadius != null);

  /// The radius for each corner.
  ///
  /// Negative radius values are clamped to 0.0 by [getInnerPath] and
  /// [getOuterPath].
  final BorderRadiusGeometry borderRadius;

  /// The style of this border.
  final BorderSide side;

  @override
  EdgeInsetsGeometry get dimensions => EdgeInsets.all(side.width);

  @override
  ShapeBorder scale(double t) {
    return ContinuousRectangleBorder(
      side: side.scale(t),
      borderRadius: borderRadius * t,
    );
  }

  @override
  ShapeBorder lerpFrom(ShapeBorder a, double t) {
    assert(t != null);
    if (a is ContinuousRectangleBorder) {
      return ContinuousRectangleBorder(
        side: BorderSide.lerp(a.side, side, t),
        borderRadius: BorderRadiusGeometry.lerp(a.borderRadius, borderRadius, t),
      );
    }
    return super.lerpFrom(a, t);
  }

  @override
  ShapeBorder lerpTo(ShapeBorder b, double t) {
    assert(t != null);
    if (b is ContinuousRectangleBorder) {
      return ContinuousRectangleBorder(
        side: BorderSide.lerp(side, b.side, t),
        borderRadius: BorderRadiusGeometry.lerp(borderRadius, b.borderRadius, t),
      );
    }
    return super.lerpTo(b, t);
  }

  double _clampToShortest(RRect rrect, double value) {
    return value > rrect.shortestSide ? rrect.shortestSide : value;
  }

  Path _getPath(RRect rrect) {
    final double left = rrect.left;
    final double right = rrect.right;
    final double top = rrect.top;
    final double bottom = rrect.bottom;
    //  Radii will be clamped to the value of the shortest side
    /// of [rrect] to avoid strange tie-fighter shapes.
    final double tlRadiusX =
      math.max(0.0, _clampToShortest(rrect, rrect.tlRadiusX));
    final double tlRadiusY =
      math.max(0.0, _clampToShortest(rrect, rrect.tlRadiusY));
    final double trRadiusX =
      math.max(0.0, _clampToShortest(rrect, rrect.trRadiusX));
    final double trRadiusY =
      math.max(0.0, _clampToShortest(rrect, rrect.trRadiusY));
    final double blRadiusX =
      math.max(0.0, _clampToShortest(rrect, rrect.blRadiusX));
    final double blRadiusY =
      math.max(0.0, _clampToShortest(rrect, rrect.blRadiusY));
    final double brRadiusX =
      math.max(0.0, _clampToShortest(rrect, rrect.brRadiusX));
    final double brRadiusY =
      math.max(0.0, _clampToShortest(rrect, rrect.brRadiusY));

    return Path()
      ..moveTo(left, top + tlRadiusX)
      ..cubicTo(left, top, left, top, left + tlRadiusY, top)
      ..lineTo(right - trRadiusX, top)
      ..cubicTo(right, top, right, top, right, top + trRadiusY)
      ..lineTo(right, bottom - brRadiusX)
      ..cubicTo(right, bottom, right, bottom, right - brRadiusY, bottom)
      ..lineTo(left + blRadiusX, bottom)
      ..cubicTo(left, bottom, left, bottom, left, bottom - blRadiusY)
      ..close();
  }

  @override
  Path getInnerPath(Rect rect, { TextDirection textDirection }) {
    return _getPath(borderRadius.resolve(textDirection).toRRect(rect).deflate(side.width));
  }

  @override
  Path getOuterPath(Rect rect, { TextDirection textDirection }) {
    return _getPath(borderRadius.resolve(textDirection).toRRect(rect));
  }

  @override
  void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
    if (rect.isEmpty)
      return;
    switch (side.style) {
      case BorderStyle.none:
        break;
      case BorderStyle.solid:
        final Path path = getOuterPath(rect, textDirection: textDirection);
        final Paint paint = side.toPaint();
        canvas.drawPath(path, paint);
        break;
    }
  }

  @override
  bool operator ==(Object other) {
    if (other.runtimeType != runtimeType)
      return false;
    return other is ContinuousRectangleBorder
        && other.side == side
        && other.borderRadius == borderRadius;
  }

  @override
  int get hashCode => hashValues(side, borderRadius);

  @override
  String toString() {
    return '${objectRuntimeType(this, 'ContinuousRectangleBorder')}($side, $borderRadius)';
  }
}