Avalonia/src/Avalonia.SceneGraph/Visual.cs

// Copyright (c) The Avalonia Project. All rights reserved.
// Licensed under the MIT license. See licence.md file in the project root for full license information.

using System;
using System.Collections.Specialized;
using System.Linq;
using System.Reactive.Linq;
using Avalonia.Animation;
using Avalonia.Collections;
using Avalonia.Data;
using Avalonia.Logging;
using Avalonia.Media;
using Avalonia.Platform;
using Avalonia.Rendering;
using Avalonia.VisualTree;

namespace Avalonia
{
    /// <summary>
    /// Base class for controls that provides rendering and related visual properties.
    /// </summary>
    /// <remarks>
    /// The <see cref="Visual"/> class acts as a node in the Avalonia scene graph and holds
    /// all the information needed for an <see cref="IRenderTarget"/> to render the control.
    /// To traverse the scene graph (aka Visual Tree), use the extension methods defined
    /// in <see cref="VisualExtensions"/>.
    /// </remarks>
    public class Visual : Animatable, IVisual
    {
        /// <summary>
        /// Defines the <see cref="Bounds"/> property.
        /// </summary>
        public static readonly DirectProperty<Visual, Rect> BoundsProperty =
            AvaloniaProperty.RegisterDirect<Visual, Rect>(nameof(Bounds), o => o.Bounds);

        /// <summary>
        /// Defines the <see cref="ClipToBounds"/> property.
        /// </summary>
        public static readonly StyledProperty<bool> ClipToBoundsProperty =
            AvaloniaProperty.Register<Visual, bool>(nameof(ClipToBounds));

        /// <summary>
        /// Defines the <see cref="Clip"/> property.
        /// </summary>
        public static readonly StyledProperty<Geometry> ClipProperty =
            AvaloniaProperty.Register<Visual, Geometry>(nameof(Clip));

        /// <summary>
        /// Defines the <see cref="IsVisibleProperty"/> property.
        /// </summary>
        public static readonly StyledProperty<bool> IsVisibleProperty =
            AvaloniaProperty.Register<Visual, bool>(nameof(IsVisible), true);

        /// <summary>
        /// Defines the <see cref="Opacity"/> property.
        /// </summary>
        public static readonly StyledProperty<double> OpacityProperty =
            AvaloniaProperty.Register<Visual, double>(nameof(Opacity), 1);

        /// <summary>
        /// Defines the <see cref="RenderTransform"/> property.
        /// </summary>
        public static readonly StyledProperty<Transform> RenderTransformProperty =
            AvaloniaProperty.Register<Visual, Transform>(nameof(RenderTransform));

        /// <summary>
        /// Defines the <see cref="RenderTransformOrigin"/> property.
        /// </summary>
        public static readonly StyledProperty<RelativePoint> RenderTransformOriginProperty =
            AvaloniaProperty.Register<Visual, RelativePoint>(nameof(RenderTransformOrigin), defaultValue: RelativePoint.Center);

        /// <summary>
        /// Defines the <see cref="IVisual.VisualParent"/> property.
        /// </summary>
        public static readonly DirectProperty<Visual, IVisual> VisualParentProperty =
            AvaloniaProperty.RegisterDirect<Visual, IVisual>("VisualParent", o => o._visualParent);

        /// <summary>
        /// Defines the <see cref="ZIndex"/> property.
        /// </summary>
        public static readonly StyledProperty<int> ZIndexProperty =
            AvaloniaProperty.Register<Visual, int>(nameof(ZIndex));

        private Rect _bounds;
        private IVisual _visualParent;

        /// <summary>
        /// Initializes static members of the <see cref="Visual"/> class.
        /// </summary>
        static Visual()
        {
            AffectsRender(BoundsProperty, IsVisibleProperty, OpacityProperty);
            RenderTransformProperty.Changed.Subscribe(RenderTransformChanged);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Visual"/> class.
        /// </summary>
        public Visual()
        {
            var visualChildren = new AvaloniaList<IVisual>();
            visualChildren.ResetBehavior = ResetBehavior.Remove;
            visualChildren.Validate = ValidateVisualChild;
            visualChildren.CollectionChanged += VisualChildrenChanged;
            VisualChildren = visualChildren;
        }

        /// <summary>
        /// Raised when the control is attached to a rooted visual tree.
        /// </summary>
        public event EventHandler<VisualTreeAttachmentEventArgs> AttachedToVisualTree;

        /// <summary>
        /// Raised when the control is detached from a rooted visual tree.
        /// </summary>
        public event EventHandler<VisualTreeAttachmentEventArgs> DetachedFromVisualTree;

        /// <summary>
        /// Gets the bounds of the scene graph node relative to its parent.
        /// </summary>
        public Rect Bounds
        {
            get { return _bounds; }
            protected set { SetAndRaise(BoundsProperty, ref _bounds, value); }
        }

        /// <summary>
        /// Gets a value indicating whether the scene graph node should be clipped to its bounds.
        /// </summary>
        public bool ClipToBounds
        {
            get { return GetValue(ClipToBoundsProperty); }
            set { SetValue(ClipToBoundsProperty, value); }
        }

        /// <summary>
        /// Gets or sets the geometry clip for this visual.
        /// </summary>
        public Geometry Clip
        {
            get { return GetValue(ClipProperty); }
            set { SetValue(ClipProperty, value); }
        }

        /// <summary>
        /// Gets a value indicating whether this scene graph node and all its parents are visible.
        /// </summary>
        public bool IsEffectivelyVisible
        {
            get { return this.GetSelfAndVisualAncestors().All(x => x.IsVisible); }
        }

        /// <summary>
        /// Gets a value indicating whether this scene graph node is visible.
        /// </summary>
        public bool IsVisible
        {
            get { return GetValue(IsVisibleProperty); }
            set { SetValue(IsVisibleProperty, value); }
        }

        /// <summary>
        /// Gets the opacity of the scene graph node.
        /// </summary>
        public double Opacity
        {
            get { return GetValue(OpacityProperty); }
            set { SetValue(OpacityProperty, value); }
        }

        /// <summary>
        /// Gets the render transform of the scene graph node.
        /// </summary>
        public Transform RenderTransform
        {
            get { return GetValue(RenderTransformProperty); }
            set { SetValue(RenderTransformProperty, value); }
        }

        /// <summary>
        /// Gets the transform origin of the scene graph node.
        /// </summary>
        public RelativePoint RenderTransformOrigin
        {
            get { return GetValue(RenderTransformOriginProperty); }
            set { SetValue(RenderTransformOriginProperty, value); }
        }

        /// <summary>
        /// Gets the Z index of the node.
        /// </summary>
        /// <remarks>
        /// Controls with a higher <see cref="ZIndex"/> will appear in front of controls with
        /// a lower ZIndex. If two controls have the same ZIndex then the control that appears
        /// later in the containing element's children collection will appear on top.
        /// </remarks>
        public int ZIndex
        {
            get { return GetValue(ZIndexProperty); }
            set { SetValue(ZIndexProperty, value); }
        }

        /// <summary>
        /// Gets the control's visual children.
        /// </summary>
        protected IAvaloniaList<IVisual> VisualChildren
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets the root of the visual tree, if the control is attached to a visual tree.
        /// </summary>
        protected IRenderRoot VisualRoot
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets a value indicating whether this scene graph node is attached to a visual root.
        /// </summary>
        bool IVisual.IsAttachedToVisualTree => VisualRoot != null;

        /// <summary>
        /// Gets the scene graph node's child nodes.
        /// </summary>
        IAvaloniaReadOnlyList<IVisual> IVisual.VisualChildren => VisualChildren;

        /// <summary>
        /// Gets the scene graph node's parent node.
        /// </summary>
        IVisual IVisual.VisualParent => _visualParent;

        /// <summary>
        /// Gets the root of the visual tree, if the control is attached to a visual tree.
        /// </summary>
        IRenderRoot IVisual.VisualRoot => VisualRoot;

        /// <summary>
        /// Invalidates the visual and queues a repaint.
        /// </summary>
        public void InvalidateVisual()
        {
            VisualRoot?.RenderQueueManager?.InvalidateRender(this);
        }

        /// <summary>
        /// Renders the visual to a <see cref="DrawingContext"/>.
        /// </summary>
        /// <param name="context">The drawing context.</param>
        public virtual void Render(DrawingContext context)
        {
            Contract.Requires<ArgumentNullException>(context != null);
        }

        /// <summary>
        /// Returns a transform that transforms the visual's coordinates into the coordinates
        /// of the specified <paramref name="visual"/>.
        /// </summary>
        /// <param name="visual">The visual to translate the coordinates to.</param>
        /// <returns>
        /// A <see cref="Matrix"/> containing the transform or null if the visuals don't share a
        /// common ancestor.
        /// </returns>
        public Matrix? TransformToVisual(IVisual visual)
        {
            var common = this.FindCommonVisualAncestor(visual);

            if (common != null)
            {
                var thisOffset = GetOffsetFrom(common, this);
                var thatOffset = GetOffsetFrom(common, visual);
                return Matrix.CreateTranslation(-thatOffset) * Matrix.CreateTranslation(thisOffset);
            }

            return null;
        }

        /// <summary>
        /// Indicates that a property change should cause <see cref="InvalidateVisual"/> to be
        /// called.
        /// </summary>
        /// <param name="properties">The properties.</param>
        /// <remarks>
        /// This method should be called in a control's static constructor with each property
        /// on the control which when changed should cause a redraw. This is similar to WPF's
        /// FrameworkPropertyMetadata.AffectsRender flag.
        /// </remarks>
        protected static void AffectsRender(params AvaloniaProperty[] properties)
        {
            foreach (var property in properties)
            {
                property.Changed.Subscribe(AffectsRenderInvalidate);
            }
        }

        /// <summary>
        /// Calls the <see cref="OnAttachedToVisualTree(VisualTreeAttachmentEventArgs)"/> method 
        /// for this control and all of its visual descendents.
        /// </summary>
        /// <param name="e">The event args.</param>
        protected virtual void OnAttachedToVisualTreeCore(VisualTreeAttachmentEventArgs e)
        {
            Logger.Verbose(LogArea.Visual, this, "Attached to visual tree");

            VisualRoot = e.Root;

            if (RenderTransform != null)
            {
                RenderTransform.Changed += RenderTransformChanged;
            }

            OnAttachedToVisualTree(e);

            if (VisualChildren != null)
            {
                foreach (Visual child in VisualChildren.OfType<Visual>())
                {
                    child.OnAttachedToVisualTreeCore(e);
                }
            }
        }

        /// <summary>
        /// Calls the <see cref="OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs)"/> method 
        /// for this control and all of its visual descendents.
        /// </summary>
        /// <param name="e">The event args.</param>
        protected virtual void OnDetachedFromVisualTreeCore(VisualTreeAttachmentEventArgs e)
        {
            Logger.Verbose(LogArea.Visual, this, "Detached from visual tree");

            VisualRoot = null;

            if (RenderTransform != null)
            {
                RenderTransform.Changed -= RenderTransformChanged;
            }

            OnDetachedFromVisualTree(e);

            if (VisualChildren != null)
            {
                foreach (Visual child in VisualChildren.OfType<Visual>())
                {
                    child.OnDetachedFromVisualTreeCore(e);
                }
            }
        }

        /// <summary>
        /// Called when the control is added to a visual tree.
        /// </summary>
        /// <param name="e">The event args.</param>
        protected virtual void OnAttachedToVisualTree(VisualTreeAttachmentEventArgs e)
        {
            AttachedToVisualTree?.Invoke(this, e);
        }

        /// <summary>
        /// Called when the control is removed from a visual tree.
        /// </summary>
        /// <param name="e">The event args.</param>
        protected virtual void OnDetachedFromVisualTree(VisualTreeAttachmentEventArgs e)
        {
            DetachedFromVisualTree?.Invoke(this, e);
        }

        /// <summary>
        /// Called when a property changes that should invalidate the visual.
        /// </summary>
        /// <param name="e">The event args.</param>
        private static void AffectsRenderInvalidate(AvaloniaPropertyChangedEventArgs e)
        {
            (e.Sender as Visual)?.InvalidateVisual();
        }

        /// <summary>
        /// Gets the visual offset from the specified ancestor.
        /// </summary>
        /// <param name="ancestor">The ancestor visual.</param>
        /// <param name="visual">The visual.</param>
        /// <returns>The visual offset.</returns>
        private static Vector GetOffsetFrom(IVisual ancestor, IVisual visual)
        {
            var result = new Vector();

            while (visual != ancestor)
            {
                result = new Vector(result.X + visual.Bounds.X, result.Y + visual.Bounds.Y);
                visual = visual.VisualParent;

                if (visual == null)
                {
                    throw new ArgumentException("'visual' is not a descendent of 'ancestor'.");
                }
            }

            return result;
        }

        /// <summary>
        /// Called when a visual's <see cref="RenderTransform"/> changes.
        /// </summary>
        /// <param name="e">The event args.</param>
        private static void RenderTransformChanged(AvaloniaPropertyChangedEventArgs e)
        {
            var sender = e.Sender as Visual;

            if (sender?.VisualRoot != null)
            {
                var oldValue = e.OldValue as Transform;
                var newValue = e.NewValue as Transform;

                if (oldValue != null)
                {
                    oldValue.Changed -= sender.RenderTransformChanged;
                }

                if (newValue != null)
                {
                    newValue.Changed += sender.RenderTransformChanged;
                }

                sender.InvalidateVisual();
            }
        }

        /// <summary>
        /// Ensures a visual child is not null and not already parented.
        /// </summary>
        /// <param name="c">The visual child.</param>
        private static void ValidateVisualChild(IVisual c)
        {
            if (c == null)
            {
                throw new ArgumentNullException("Cannot add null to VisualChildren.");
            }

            if (c.VisualParent != null)
            {
                throw new InvalidOperationException("The control already has a visual parent.");
            }
        }

        /// <summary>
        /// Called when the <see cref="RenderTransform"/>'s <see cref="Transform.Changed"/> event
        /// is fired.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The event args.</param>
        private void RenderTransformChanged(object sender, EventArgs e)
        {
            InvalidateVisual();
        }

        /// <summary>
        /// Sets the visual parent of the Visual.
        /// </summary>
        /// <param name="value">The visual parent.</param>
        private void SetVisualParent(Visual value)
        {
            if (_visualParent == value)
            {
                return;
            }
            
            var old = _visualParent;
            _visualParent = value;

            if (VisualRoot != null)
            {
                var e = new VisualTreeAttachmentEventArgs(VisualRoot);
                OnDetachedFromVisualTreeCore(e);
            }

            if (_visualParent is IRenderRoot || _visualParent?.IsAttachedToVisualTree == true)
            {
                var root = this.GetVisualAncestors().OfType<IRenderRoot>().FirstOrDefault();
                var e = new VisualTreeAttachmentEventArgs(root);
                OnAttachedToVisualTreeCore(e);
            }

            RaisePropertyChanged(VisualParentProperty, old, value, BindingPriority.LocalValue);
        }

        /// <summary>
        /// Called when the <see cref="VisualChildren"/> collection changes.
        /// </summary>
        /// <param name="sender">The sender.</param>
        /// <param name="e">The event args.</param>
        private void VisualChildrenChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    foreach (Visual v in e.NewItems)
                    {
                        v.SetVisualParent(this);
                    }

                    break;

                case NotifyCollectionChangedAction.Remove:
                    foreach (Visual v in e.OldItems)
                    {
                        v.SetVisualParent(null);
                    }

                    break;
            }
        }
    }
}