Avalonia/src/Avalonia.Controls/Slider.cs

using System;
using Avalonia.Collections;
using Avalonia.Automation.Peers;
using Avalonia.Controls.Metadata;
using Avalonia.Controls.Mixins;
using Avalonia.Controls.Primitives;
using Avalonia.Data;
using Avalonia.Input;
using Avalonia.Interactivity;
using Avalonia.Layout;
using Avalonia.Utilities;
using Avalonia.Automation;

namespace Avalonia.Controls
{
    /// <summary>
    /// Enum which describes how to position the ticks in a <see cref="Slider"/>.
    /// </summary>
    public enum TickPlacement
    {
        /// <summary>
        /// No tick marks will appear.
        /// </summary>
        None,

        /// <summary>
        /// Tick marks  will appear above the track for a horizontal <see cref="Slider"/>, or to the left of the track for a vertical <see cref="Slider"/>.
        /// </summary>
        TopLeft,

        /// <summary>
        /// Tick marks will appear below the track for a horizontal <see cref="Slider"/>, or to the right of the track for a vertical <see cref="Slider"/>.
        /// </summary>
        BottomRight,

        /// <summary>
        /// Tick marks appear on both sides of either a horizontal or vertical <see cref="Slider"/>.
        /// </summary>
        Outside
    }

    /// <summary>
    /// A control that lets the user select from a range of values by moving a Thumb control along a Track.
    /// </summary>
    [TemplatePart("PART_DecreaseButton", typeof(Button))]
    [TemplatePart("PART_IncreaseButton", typeof(Button))]
    [TemplatePart("PART_Track",          typeof(Track))]
    [PseudoClasses(":vertical", ":horizontal", ":pressed")]
    public class Slider : RangeBase
    {
        /// <summary>
        /// Defines the <see cref="Orientation"/> property.
        /// </summary>
        public static readonly StyledProperty<Orientation> OrientationProperty =
            ScrollBar.OrientationProperty.AddOwner<Slider>();

        /// <summary>
        /// Defines the <see cref="IsDirectionReversed"/> property.
        /// </summary>
        public static readonly StyledProperty<bool> IsDirectionReversedProperty =
            Track.IsDirectionReversedProperty.AddOwner<Slider>();

        /// <summary>
        /// Defines the <see cref="IsSnapToTickEnabled"/> property.
        /// </summary>
        public static readonly StyledProperty<bool> IsSnapToTickEnabledProperty =
            AvaloniaProperty.Register<Slider, bool>(nameof(IsSnapToTickEnabled), false);

        /// <summary>
        /// Defines the <see cref="TickFrequency"/> property.
        /// </summary>
        public static readonly StyledProperty<double> TickFrequencyProperty =
            AvaloniaProperty.Register<Slider, double>(nameof(TickFrequency), 0.0);

        /// <summary>
        /// Defines the <see cref="TickPlacement"/> property.
        /// </summary>
        public static readonly StyledProperty<TickPlacement> TickPlacementProperty =
            AvaloniaProperty.Register<TickBar, TickPlacement>(nameof(TickPlacement), 0d);

        /// <summary>
        /// Defines the <see cref="TicksProperty"/> property.
        /// </summary>
        public static readonly StyledProperty<AvaloniaList<double>> TicksProperty =
            TickBar.TicksProperty.AddOwner<Slider>();

        // Slider required parts
        private bool _isDragging = false;
        private Track? _track;
        private Button? _decreaseButton;
        private Button? _increaseButton;
        private IDisposable? _decreaseButtonPressDispose;
        private IDisposable? _decreaseButtonReleaseDispose;
        private IDisposable? _increaseButtonSubscription;
        private IDisposable? _increaseButtonReleaseDispose;
        private IDisposable? _pointerMovedDispose;

        private const double Tolerance = 0.0001;

        /// <summary>
        /// Initializes static members of the <see cref="Slider"/> class. 
        /// </summary>
        static Slider()
        {
            PressedMixin.Attach<Slider>();
            FocusableProperty.OverrideDefaultValue<Slider>(true);
            OrientationProperty.OverrideDefaultValue(typeof(Slider), Orientation.Horizontal);
            Thumb.DragStartedEvent.AddClassHandler<Slider>((x, e) => x.OnThumbDragStarted(e), RoutingStrategies.Bubble);
            Thumb.DragCompletedEvent.AddClassHandler<Slider>((x, e) => x.OnThumbDragCompleted(e),
                RoutingStrategies.Bubble);

            ValueProperty.OverrideMetadata<Slider>(new DirectPropertyMetadata<double>(enableDataValidation: true));
            AutomationProperties.ControlTypeOverrideProperty.OverrideDefaultValue<Slider>(AutomationControlType.Slider);
        }

        /// <summary>
        /// Instantiates a new instance of the <see cref="Slider"/> class. 
        /// </summary>
        public Slider()
        {
            UpdatePseudoClasses(Orientation);
        }

        /// <summary>
        /// Defines the ticks to be drawn on the tick bar.
        /// </summary>
        public AvaloniaList<double> Ticks
        {
            get => GetValue(TicksProperty);
            set => SetValue(TicksProperty, value);
        }

        /// <summary>
        /// Gets or sets the orientation of a <see cref="Slider"/>.
        /// </summary>
        public Orientation Orientation
        {
            get { return GetValue(OrientationProperty); }
            set { SetValue(OrientationProperty, value); }
        }

        /// <summary>
        /// Gets or sets the direction of increasing value.
        /// </summary>
        /// <value>
        /// true if the direction of increasing value is to the left for a horizontal slider or
        /// down for a vertical slider; otherwise, false. The default is false.
        /// </value>
        public bool IsDirectionReversed
        {
            get { return GetValue(IsDirectionReversedProperty); }
            set { SetValue(IsDirectionReversedProperty, value); }
        }

        /// <summary>
        /// Gets or sets a value that indicates whether the <see cref="Slider"/> automatically moves the <see cref="Thumb"/> to the closest tick mark.
        /// </summary>
        public bool IsSnapToTickEnabled
        {
            get { return GetValue(IsSnapToTickEnabledProperty); }
            set { SetValue(IsSnapToTickEnabledProperty, value); }
        }

        /// <summary>
        /// Gets or sets the interval between tick marks.
        /// </summary>
        public double TickFrequency
        {
            get { return GetValue(TickFrequencyProperty); }
            set { SetValue(TickFrequencyProperty, value); }
        }

        /// <summary>
        /// Gets or sets a value that indicates where to draw 
        /// tick marks in relation to the track.
        /// </summary>
        public TickPlacement TickPlacement
        {
            get { return GetValue(TickPlacementProperty); }
            set { SetValue(TickPlacementProperty, value); }
        }

        /// <inheritdoc/>
        protected override void OnApplyTemplate(TemplateAppliedEventArgs e)
        {
            base.OnApplyTemplate(e);

            _decreaseButtonPressDispose?.Dispose();
            _decreaseButtonReleaseDispose?.Dispose();
            _increaseButtonSubscription?.Dispose();
            _increaseButtonReleaseDispose?.Dispose();
            _pointerMovedDispose?.Dispose();
            
            _decreaseButton = e.NameScope.Find<Button>("PART_DecreaseButton");
            _track = e.NameScope.Find<Track>("PART_Track");
            _increaseButton = e.NameScope.Find<Button>("PART_IncreaseButton");

            if (_track != null)
            {
                _track.IsThumbDragHandled = true;
            }

            if (_decreaseButton != null)
            {
                _decreaseButtonPressDispose = _decreaseButton.AddDisposableHandler(PointerPressedEvent, TrackPressed, RoutingStrategies.Tunnel);
                _decreaseButtonReleaseDispose = _decreaseButton.AddDisposableHandler(PointerReleasedEvent, TrackReleased, RoutingStrategies.Tunnel);
            }

            if (_increaseButton != null)
            {
                _increaseButtonSubscription = _increaseButton.AddDisposableHandler(PointerPressedEvent, TrackPressed, RoutingStrategies.Tunnel);
                _increaseButtonReleaseDispose = _increaseButton.AddDisposableHandler(PointerReleasedEvent, TrackReleased, RoutingStrategies.Tunnel);
            }

            _pointerMovedDispose = this.AddDisposableHandler(PointerMovedEvent, TrackMoved, RoutingStrategies.Tunnel);
        }

        protected override void OnKeyDown(KeyEventArgs e)
        {
            base.OnKeyDown(e);

            if (e.Handled || e.KeyModifiers != KeyModifiers.None) return;

            var handled = true;

            switch (e.Key)
            {
                case Key.Down:
                case Key.Left:
                    MoveToNextTick(IsDirectionReversed ? SmallChange : -SmallChange);
                    break;

                case Key.Up:
                case Key.Right:
                    MoveToNextTick(IsDirectionReversed ? -SmallChange : SmallChange);
                    break;

                case Key.PageUp:
                    MoveToNextTick(IsDirectionReversed ? -LargeChange : LargeChange);
                    break;

                case Key.PageDown:
                    MoveToNextTick(IsDirectionReversed ? LargeChange : -LargeChange);
                    break;

                case Key.Home:
                    Value = Minimum;
                    break;

                case Key.End:
                    Value = Maximum;
                    break;

                default:
                    handled = false;
                    break;
            }

            e.Handled = handled;
        }
            
        private void MoveToNextTick(double direction)
        {
            if (direction == 0.0) return;

            var value = Value;

            // Find the next value by snapping
            var next = SnapToTick(Math.Max(Minimum, Math.Min(Maximum, value + direction)));

            var greaterThan = direction > 0; //search for the next tick greater than value?

            // If the snapping brought us back to value, find the next tick point
            if (Math.Abs(next - value) < Tolerance
                && !(greaterThan && Math.Abs(value - Maximum) < Tolerance) // Stop if searching up if already at Max
                && !(!greaterThan && Math.Abs(value - Minimum) < Tolerance)) // Stop if searching down if already at Min
            {
                var ticks = Ticks;

                // If ticks collection is available, use it.
                // Note that ticks may be unsorted.
                if (ticks != null && ticks.Count > 0)
                {
                    foreach (var tick in ticks)
                    {
                        // Find the smallest tick greater than value or the largest tick less than value
                        if (greaterThan && MathUtilities.GreaterThan(tick, value) &&
                            (MathUtilities.LessThan(tick, next) || Math.Abs(next - value) < Tolerance)
                            || !greaterThan && MathUtilities.LessThan(tick, value) &&
                            (MathUtilities.GreaterThan(tick, next) || Math.Abs(next - value) < Tolerance))
                        {
                            next = tick;
                        }
                    }
                }
                else if (MathUtilities.GreaterThan(TickFrequency, 0.0))
                {
                    // Find the current tick we are at
                    var tickNumber = Math.Round((value - Minimum) / TickFrequency);

                    if (greaterThan)
                        tickNumber += 1.0;
                    else
                        tickNumber -= 1.0;

                    next = Minimum + tickNumber * TickFrequency;
                }
            }


            // Update if we've found a better value
            if (Math.Abs(next - value) > Tolerance)
            {
                Value = next;
            }
        }

        private void TrackMoved(object? sender, PointerEventArgs e)
        {
            if (_isDragging)
            {
                MoveToPoint(e.GetCurrentPoint(_track));
            }
        }

        private void TrackReleased(object? sender, PointerReleasedEventArgs e)
        {
            _isDragging = false;
        }

        private void TrackPressed(object? sender, PointerPressedEventArgs e)
        {
            if (e.GetCurrentPoint(this).Properties.IsLeftButtonPressed)
            {
                MoveToPoint(e.GetCurrentPoint(_track));
                _isDragging = true;
            }
        }

        private void MoveToPoint(PointerPoint posOnTrack)
        {
            if (_track is null)
                return;

            var orient = Orientation == Orientation.Horizontal;
            var thumbLength = (orient 
                ? _track.Thumb.Bounds.Width 
                : _track.Thumb.Bounds.Height) + double.Epsilon;
            var trackLength = (orient 
                ? _track.Bounds.Width 
                : _track.Bounds.Height) - thumbLength;
            var trackPos = orient ? posOnTrack.Position.X : posOnTrack.Position.Y;
            var logicalPos = MathUtilities.Clamp((trackPos - thumbLength * 0.5) / trackLength, 0.0d, 1.0d);
            var invert = orient ? 
                IsDirectionReversed ? 1 : 0 :
                IsDirectionReversed ? 0 : 1;
            var calcVal = Math.Abs(invert - logicalPos);
            var range = Maximum - Minimum;
            var finalValue = calcVal * range + Minimum;

            Value = IsSnapToTickEnabled ? SnapToTick(finalValue) : finalValue;
        }

        protected override void UpdateDataValidation(
            AvaloniaProperty property,
            BindingValueType state,
            Exception? error)
        {
            if (property == ValueProperty)
            {
                DataValidationErrors.SetError(this, error);
            }
        }

        protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
        {
            base.OnPropertyChanged(change);

            if (change.Property == OrientationProperty)
            {
                UpdatePseudoClasses(change.GetNewValue<Orientation>());
            }
        }

        /// <summary>
        /// Called when user start dragging the <see cref="Thumb"/>.
        /// </summary>
        /// <param name="e"></param>
        protected virtual void OnThumbDragStarted(VectorEventArgs e)
        {
            _isDragging = true;
        }

        /// <summary>
        /// Called when user stop dragging the <see cref="Thumb"/>.
        /// </summary>
        /// <param name="e"></param>
        protected virtual void OnThumbDragCompleted(VectorEventArgs e)
        {
            _isDragging = false;
        }

        /// <summary>
        /// Snap the input 'value' to the closest tick.
        /// </summary>
        /// <param name="value">Value that want to snap to closest Tick.</param>
        private double SnapToTick(double value)
        {
            if (IsSnapToTickEnabled)
            {
                var previous = Minimum;
                var next = Maximum;

                // This property is rarely set so let's try to avoid the GetValue
                var ticks = Ticks;

                // If ticks collection is available, use it.
                // Note that ticks may be unsorted.
                if (ticks != null && ticks.Count > 0)
                {
                    foreach (var tick in ticks)
                    {
                        if (MathUtilities.AreClose(tick, value))
                        {
                            return value;
                        }

                        if (MathUtilities.LessThan(tick, value) && MathUtilities.GreaterThan(tick, previous))
                        {
                            previous = tick;
                        }
                        else if (MathUtilities.GreaterThan(tick, value) && MathUtilities.LessThan(tick, next))
                        {
                            next = tick;
                        }
                    }
                }
                else if (MathUtilities.GreaterThan(TickFrequency, 0.0))
                {
                    previous = Minimum + Math.Round((value - Minimum) / TickFrequency) * TickFrequency;
                    next = Math.Min(Maximum, previous + TickFrequency);
                }

                // Choose the closest value between previous and next. If tie, snap to 'next'.
                value = MathUtilities.GreaterThanOrClose(value, (previous + next) * 0.5) ? next : previous;
            }

            return value;
        }


        private void UpdatePseudoClasses(Orientation o)
        {
            PseudoClasses.Set(":vertical", o == Orientation.Vertical);
            PseudoClasses.Set(":horizontal", o == Orientation.Horizontal);
        }
    }
}