packages/flutter/lib/src/cupertino/thumb_painter.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.

/// @docImport 'slider.dart';
/// @docImport 'switch.dart';
library;

import 'package:flutter/painting.dart';

import 'colors.dart';

const Color _kThumbBorderColor = Color(0x0A000000);

const List<BoxShadow> _kSwitchBoxShadows = <BoxShadow>[
  BoxShadow(color: Color(0x26000000), offset: Offset(0, 3), blurRadius: 8.0),
  BoxShadow(color: Color(0x0F000000), offset: Offset(0, 3), blurRadius: 1.0),
];

const List<BoxShadow> _kSliderBoxShadows = <BoxShadow>[
  BoxShadow(color: Color(0x26000000), offset: Offset(0, 3), blurRadius: 8.0),
  BoxShadow(color: Color(0x29000000), offset: Offset(0, 1), blurRadius: 1.0),
  BoxShadow(color: Color(0x1A000000), offset: Offset(0, 3), blurRadius: 1.0),
];

/// Paints an iOS-style slider thumb or switch thumb.
///
/// Used by [CupertinoSlider].
class CupertinoThumbPainter {
  /// Creates an object that paints an iOS-style slider thumb.
  const CupertinoThumbPainter({
    this.color = CupertinoColors.white,
    this.shadows = _kSliderBoxShadows,
  });

  /// Creates an object that paints an iOS-style switch thumb.
  const CupertinoThumbPainter.switchThumb({
    Color color = CupertinoColors.white,
    List<BoxShadow> shadows = _kSwitchBoxShadows,
  }) : this(color: color, shadows: shadows);

  /// The color of the interior of the thumb.
  final Color color;

  /// The list of [BoxShadow] to paint below the thumb.
  final List<BoxShadow> shadows;

  /// Half the default diameter of the thumb.
  static const double radius = 14.0;

  /// The default amount the thumb should be extended horizontally when pressed.
  static const double extension = 7.0;

  /// Paints the thumb onto the given canvas in the given rectangle.
  ///
  /// Consider using [radius] and [extension] when deciding how large a
  /// rectangle to use for the thumb.
  void paint(Canvas canvas, Rect rect) {
    // Paint RRects instead of RSuperellipses here, because practically
    // [CupertinoSlider] only draws circular thumbs.
    final thumbShape = RRect.fromRectAndRadius(rect, Radius.circular(rect.shortestSide / 2.0));

    for (final BoxShadow shadow in shadows) {
      canvas.drawRRect(thumbShape.shift(shadow.offset), shadow.toPaint());
    }

    canvas.drawRRect(thumbShape.inflate(0.5), Paint()..color = _kThumbBorderColor);
    canvas.drawRRect(thumbShape, Paint()..color = color);
  }
}