Add live display support

This commit also adds functionality to LiveRenderable that should
fix some problems related to vertical overflow.

Closes #316
Closes #415

src/Spectre.Console/Rendering/LiveRenderable.cs

@@ -1,4 +1,6 @@
+using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using static Spectre.Console.AnsiSequences;
 
 namespace Spectre.Console.Rendering
@@ -6,12 +8,33 @@ namespace Spectre.Console.Rendering
     internal sealed class LiveRenderable : Renderable
     {
         private readonly object _lock = new object();
+        private readonly IAnsiConsole _console;
         private IRenderable? _renderable;
         private SegmentShape? _shape;
 
-        public bool HasRenderable => _renderable != null;
+        public IRenderable? Target => _renderable;
+        public bool DidOverflow { get; private set; }
 
-        public void SetRenderable(IRenderable renderable)
+        [MemberNotNullWhen(true, nameof(Target))]
+        public bool HasRenderable => _renderable != null;
+        public VerticalOverflow Overflow { get; set; }
+        public VerticalOverflowCropping OverflowCropping { get; set; }
+
+        public LiveRenderable(IAnsiConsole console)
+        {
+            _console = console ?? throw new ArgumentNullException(nameof(console));
+
+            Overflow = VerticalOverflow.Ellipsis;
+            OverflowCropping = VerticalOverflowCropping.Top;
+        }
+
+        public LiveRenderable(IAnsiConsole console, IRenderable renderable)
+            : this(console)
+        {
+            _renderable = renderable ?? throw new ArgumentNullException(nameof(renderable));
+        }
+
+        public void SetRenderable(IRenderable? renderable)
         {
             lock (_lock)
             {
@@ -51,12 +74,61 @@ namespace Spectre.Console.Rendering
         {
             lock (_lock)
             {
+                DidOverflow = false;
+
                 if (_renderable != null)
                 {
                     var segments = _renderable.Render(context, maxWidth);
                     var lines = Segment.SplitLines(segments);
 
                     var shape = SegmentShape.Calculate(context, lines);
+                    if (shape.Height > _console.Profile.Height)
+                    {
+                        if (Overflow == VerticalOverflow.Crop)
+                        {
+                            if (OverflowCropping == VerticalOverflowCropping.Bottom)
+                            {
+                                // Remove bottom lines
+                                var index = Math.Min(_console.Profile.Height, lines.Count);
+                                var count = lines.Count - index;
+                                lines.RemoveRange(index, count);
+                            }
+                            else
+                            {
+                                // Remove top lines
+                                var start = lines.Count - _console.Profile.Height;
+                                lines.RemoveRange(0, start);
+                            }
+
+                            shape = SegmentShape.Calculate(context, lines);
+                        }
+                        else if (Overflow == VerticalOverflow.Ellipsis)
+                        {
+                            var ellipsisText = _console.Profile.Capabilities.Unicode ? "…" : "...";
+                            var ellipsis = new SegmentLine(((IRenderable)new Markup($"[yellow]{ellipsisText}[/]")).Render(context, maxWidth));
+
+                            if (OverflowCropping == VerticalOverflowCropping.Bottom)
+                            {
+                                // Remove bottom lines
+                                var index = Math.Min(_console.Profile.Height - 1, lines.Count);
+                                var count = lines.Count - index;
+                                lines.RemoveRange(index, count);
+                                lines.Add(ellipsis);
+                            }
+                            else
+                            {
+                                // Remove top lines
+                                var start = lines.Count - _console.Profile.Height;
+                                lines.RemoveRange(0, start + 1);
+                                lines.Insert(0, ellipsis);
+                            }
+
+                            shape = SegmentShape.Calculate(context, lines);
+                        }
+
+                        DidOverflow = true;
+                    }
+
                     _shape = _shape == null ? shape : _shape.Value.Inflate(shape);
                     _shape.Value.Apply(context, ref lines);
 

src/Spectre.Console/Rendering/SegmentLine.cs

@@ -13,6 +13,22 @@ namespace Spectre.Console.Rendering
         /// </summary>
         public int Length => this.Sum(line => line.Text.Length);
 
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SegmentLine"/> class.
+        /// </summary>
+        public SegmentLine()
+        {
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SegmentLine"/> class.
+        /// </summary>
+        /// <param name="segments">The segments.</param>
+        public SegmentLine(IEnumerable<Segment> segments)
+            : base(segments)
+        {
+        }
+
         /// <summary>
         /// Gets the number of cells the segment line occupies.
         /// </summary>