Fill not render space (Render engine, Border)

src/ConsoleApp/FileTime.ConsoleUI.App/Controls/CommandPalette.cs

@@ -2,6 +2,7 @@
 using FileTime.App.CommandPalette.ViewModels;
 using FileTime.ConsoleUI.App.Styling;
 using GeneralInputKey;
+using TerminalUI.Color;
 using TerminalUI.Controls;
 using TerminalUI.Extensions;
 using TerminalUI.Models;
@@ -59,6 +60,7 @@ public class CommandPalette
             Margin = 5,
             Padding = 1,
             MaxWidth = 50,
+            Fill = SpecialColor.None,
             Content = new Grid<IRootViewModel>
             {
                 RowDefinitionsObject = "Auto *",

src/Library/TerminalUI.Examples/Controls/ProgressBarExamples.cs

@@ -52,14 +52,16 @@ public class ProgressBarExamples
 
     private void RenderProgressBar<T>(ProgressBar<T> progressBar, Position position)
     {
+        var s = new Size(10, 1);
         var renderContext = new RenderContext(
             _driver,
             true,
             null,
             null,
             new(),
-            new TextFormatContext(true)
+            new TextFormatContext(true),
+            new bool[s.Width,s.Height]
         );
-        progressBar.Render(renderContext, position, new Size(10, 1));
+        progressBar.Render(renderContext, position, s);
     }
 }

src/Library/TerminalUI/Array2DHelper.cs

@@ -0,0 +1,96 @@
+using TerminalUI.ConsoleDrivers;
+using TerminalUI.Models;
+
+namespace TerminalUI;
+
+public static class Array2DHelper
+{
+    public static void CombineArray2Ds<T, TResult>(T[,] array1, T[,] array2, Position array2Delta, TResult[,] array3, Func<T?, T?, TResult> func)
+        where T : struct
+        where TResult : struct
+    {
+        var array1Size = new Size(array1.GetLength(0), array1.GetLength(1));
+        var array2Size = new Size(array2.GetLength(0), array2.GetLength(1));
+        var array3Size = new Size(array3.GetLength(0), array3.GetLength(1));
+
+        var maxX = int.Max(array1Size.Width, array2Size.Width + array2Delta.X);
+        maxX = int.Max(maxX, array3Size.Width);
+
+        var maxY = int.Max(array1Size.Height, array2Size.Height + array2Delta.Y);
+        maxY = int.Max(maxY, array3Size.Height);
+
+
+        for (var x = 0; x < maxX; x++)
+        {
+            for (var y = 0; y < maxY; y++)
+            {
+                if (x >= array3Size.Width
+                    || y >= array3Size.Height) continue;
+
+                T? v1 = x < array1Size.Width && y < array1Size.Height ? array1[x, y] : null;
+
+
+                var array2X = x - array2Delta.X;
+                var array2Y = y - array2Delta.Y;
+                T? v2 = array2X >= 0
+                        && array2X < array2Size.Width
+                        && array2Y >= 0
+                        && array2Y < array2Size.Height
+                    ? array2[array2X, array2Y]
+                    : null;
+
+                array3[x, y] = func(v1, v2);
+            }
+        }
+    }
+
+    public static void RenderEmpty(
+        IConsoleDriver driver,
+        bool[,] updatedCells,
+        bool[,] resultCells,
+        char fillChar,
+        Position position,
+        Size size
+    )
+    {
+        var endX = position.X + size.Width;
+        var endY = position.Y + size.Height;
+        for (var y = position.Y; y < endY; y++)
+        {
+            for (var x = position.X; x < endX; x++)
+            {
+                if (updatedCells[x, y]) continue;
+
+                var startIndex = x;
+                while (x < endX && !updatedCells[x, y])
+                {
+                    x++;
+                }
+
+                RenderEmpty(driver, resultCells, fillChar, startIndex, x, y);
+            }
+        }
+    }
+
+    private static void RenderEmpty(
+        IConsoleDriver driver,
+        bool[,] resultCells,
+        char fillChar,
+        int startX,
+        int endX,
+        int y
+    )
+    {
+        var length = endX - startX;
+        Span<char> text = stackalloc char[length];
+        text.Fill(fillChar);
+
+        driver.SetCursorPosition(new Position(startX, y));
+        driver.Write(text);
+
+        for (var x = startX; x < endX; x++)
+        {
+            resultCells[x, y] = true;
+        }
+    }
+}

src/Library/TerminalUI/Controls/Border.cs

@@ -1,4 +1,5 @@
 using PropertyChanged.SourceGenerator;
+using TerminalUI.Color;
 using TerminalUI.Models;
 using TerminalUI.Traits;
 
@@ -16,6 +17,7 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
     [Notify] private char _topRightChar = '┐';
     [Notify] private char _bottomLeftChar = '└';
     [Notify] private char _bottomRightChar = '┘';
+    [Notify] private IColor? _fill;
 
     public Border()
     {
@@ -25,6 +27,9 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
         RerenderProperties.Add(nameof(LeftChar));
         RerenderProperties.Add(nameof(RightChar));
         RerenderProperties.Add(nameof(BottomChar));
+        RerenderProperties.Add(nameof(TopLeftChar));
+        RerenderProperties.Add(nameof(TopRightChar));
+        RerenderProperties.Add(nameof(Fill));
     }
 
     protected override Size CalculateSize()
@@ -51,12 +56,19 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
                 + DataContext?.GetType().Name);
         }
 
+        var backgroundColor = Background ?? renderContext.Background;
+        var foregroundColor = Foreground ?? renderContext.Foreground;
+        var fillColor = Fill ?? Background ?? renderContext.Background;
+
         var childPosition = new Position(X: position.X + _borderThickness.Left, Y: position.Y + _borderThickness.Top);
         var childSize = new Size(
             Width: size.Width - _borderThickness.Left - _borderThickness.Right,
             Height: size.Height - _borderThickness.Top - _borderThickness.Bottom
         );
 
+        var childPositionWithoutPadding = childPosition;
+        var childSizeWithoutPadding = childSize;
+
         if (_padding.Left > 0 || _padding.Top > 0 || _padding.Right > 0 || _padding.Bottom > 0)
         {
             childPosition = new Position(X: childPosition.X + _padding.Left, Y: childPosition.Y + _padding.Top);
@@ -66,85 +78,117 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
             );
         }
 
-        var contentRendered = ContentRendererMethod(renderContext, childPosition, childSize);
+        // Same size as the original.
+        // Although wasting memory, but we would have to delta the position when setting "updatedcells"
+        // It is easier and also covers the fact the children use a different array
+        var borderChildUpdatedCells = new bool[
+            renderContext.UpdatedCells.GetLength(0),
+            renderContext.UpdatedCells.GetLength(1)
+        ];
+        var childRenderContext = renderContext with {UpdatedCells = borderChildUpdatedCells};
+
+        var contentRendered = ContentRendererMethod(childRenderContext, childPosition, childSize);
 
         if (contentRendered)
         {
             var driver = renderContext.ConsoleDriver;
             driver.ResetStyle();
-            SetColorsForDriver(renderContext);
+            SetStyleColor(renderContext, foregroundColor, backgroundColor);
+        }
 
-            RenderTopBorder(renderContext, position, size);
+        var updateCellsOnly = !contentRendered;
-            RenderBottomBorder(renderContext, position, size);
+        RenderTopBorder(renderContext, position, size, updateCellsOnly);
-            RenderLeftBorder(renderContext, position, size);
+        RenderBottomBorder(renderContext, position, size, updateCellsOnly);
-            RenderRightBorder(renderContext, position, size);
+        RenderLeftBorder(renderContext, position, size, updateCellsOnly);
+        RenderRightBorder(renderContext, position, size, updateCellsOnly);
 
-            RenderTopLeftCorner(renderContext, position);
+        RenderTopLeftCorner(renderContext, position, updateCellsOnly);
-            RenderTopRightCorner(renderContext, position, size);
+        RenderTopRightCorner(renderContext, position, size, updateCellsOnly);
-            RenderBottomLeftCorner(renderContext, position, size);
+        RenderBottomLeftCorner(renderContext, position, size, updateCellsOnly);
-            RenderBottomRightCorner(renderContext, position, size);
+        RenderBottomRightCorner(renderContext, position, size, updateCellsOnly);
 
-            //TODO render padding
+        if (fillColor != null)
+        {
+            SetStyleColor(renderContext, foregroundColor, fillColor);
+            
+            // Use the same array that children use. Also use that area, so we working only inside the border 
+            Array2DHelper.RenderEmpty(
+                renderContext.ConsoleDriver,
+                borderChildUpdatedCells,
+                borderChildUpdatedCells,
+                ApplicationContext!.EmptyCharacter,
+                childPositionWithoutPadding,
+                childSizeWithoutPadding
+            );
+
+            //Write back the changes to the original array
+            Array2DHelper.CombineArray2Ds(
+                renderContext.UpdatedCells,
+                borderChildUpdatedCells,
+                new Position(0, 0),
+                renderContext.UpdatedCells,
+                (a, b) => (a ?? false) || (b ?? false)
+            );
         }
 
         return contentRendered;
     }
 
-    private void RenderTopBorder(in RenderContext renderContext, Position position, Size size)
+    private void RenderTopBorder(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         position = position with {X = position.X + _borderThickness.Left};
         size = new Size(Width: size.Width - _borderThickness.Left - _borderThickness.Right, Height: _borderThickness.Top);
-        RenderText(_topChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_topChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderBottomBorder(in RenderContext renderContext, Position position, Size size)
+    private void RenderBottomBorder(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         position = new Position(X: position.X + _borderThickness.Left, Y: position.Y + size.Height - _borderThickness.Bottom);
         size = new Size(Width: size.Width - _borderThickness.Left - _borderThickness.Right, Height: _borderThickness.Bottom);
-        RenderText(_bottomChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_bottomChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderLeftBorder(in RenderContext renderContext, Position position, Size size)
+    private void RenderLeftBorder(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         position = position with {Y = position.Y + _borderThickness.Top};
         size = new Size(Width: _borderThickness.Left, Height: size.Height - _borderThickness.Top - _borderThickness.Bottom);
-        RenderText(_leftChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_leftChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderRightBorder(in RenderContext renderContext, Position position, Size size)
+    private void RenderRightBorder(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         position = new Position(X: position.X + size.Width - _borderThickness.Right, Y: position.Y + _borderThickness.Top);
         size = new Size(Width: _borderThickness.Right, Height: size.Height - _borderThickness.Top - _borderThickness.Bottom);
-        RenderText(_rightChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_rightChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderTopLeftCorner(in RenderContext renderContext, Position position)
+    private void RenderTopLeftCorner(in RenderContext renderContext, Position position, bool updateCellsOnly)
     {
         if (_borderThickness.Left == 0 || _borderThickness.Top == 0) return;
 
         var size = new Size(Width: _borderThickness.Left, Height: _borderThickness.Top);
-        RenderText(_topLeftChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_topLeftChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderTopRightCorner(in RenderContext renderContext, Position position, Size size)
+    private void RenderTopRightCorner(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         if (_borderThickness.Right == 0 || _borderThickness.Top == 0) return;
 
         position = position with {X = position.X + size.Width - _borderThickness.Right};
         size = new Size(Width: _borderThickness.Right, Height: _borderThickness.Top);
-        RenderText(_topRightChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_topRightChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderBottomLeftCorner(in RenderContext renderContext, Position position, Size size)
+    private void RenderBottomLeftCorner(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         if (_borderThickness.Left == 0 || _borderThickness.Bottom == 0) return;
 
         position = position with {Y = position.Y + size.Height - _borderThickness.Bottom};
         size = new Size(Width: _borderThickness.Left, Height: _borderThickness.Bottom);
-        RenderText(_bottomLeftChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_bottomLeftChar, renderContext, position, size, updateCellsOnly);
     }
 
-    private void RenderBottomRightCorner(in RenderContext renderContext, Position position, Size size)
+    private void RenderBottomRightCorner(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         if (_borderThickness.Right == 0 || _borderThickness.Bottom == 0) return;
 
@@ -153,6 +197,6 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
             Y: position.Y + size.Height - _borderThickness.Bottom
         );
         size = new Size(Width: _borderThickness.Right, Height: _borderThickness.Bottom);
-        RenderText(_bottomRightChar, renderContext.ConsoleDriver, position, size);
+        RenderText(_bottomRightChar, renderContext, position, size, updateCellsOnly);
     }
 }

src/Library/TerminalUI/Controls/ChildCollectionView.cs

@@ -4,7 +4,7 @@ using System.Diagnostics.CodeAnalysis;
 
 namespace TerminalUI.Controls;
 
-public abstract class ChildContainerView<TConcrete, T>
+public abstract class ChildCollectionView<TConcrete, T>
     : View<TConcrete, T>, IChildContainer<T>
     where TConcrete : View<TConcrete, T>
 {
@@ -12,7 +12,7 @@ public abstract class ChildContainerView<TConcrete, T>
     public ReadOnlyObservableCollection<IView> Children { get; }
     public ChildInitializer<T> ChildInitializer { get; }
 
-    protected ChildContainerView()
+    protected ChildCollectionView()
     {
         ChildInitializer = new ChildInitializer<T>(this);
         Children = new ReadOnlyObservableCollection<IView>(_children);

src/Library/TerminalUI/Controls/ContentView.cs

@@ -48,7 +48,7 @@ public abstract partial class ContentView<TConcrete, T>
         {
             if (_placeholderRenderDone) return false;
             _placeholderRenderDone = true;
-            RenderEmpty(renderContext, position, size);
+            RenderEmpty(renderContext, position, size, false);
             return true;
         }
 

src/Library/TerminalUI/Controls/Grid.cs

@@ -7,7 +7,7 @@ using TerminalUI.ViewExtensions;
 
 namespace TerminalUI.Controls;
 
-public sealed class Grid<T> : ChildContainerView<Grid<T>, T>, IVisibilityChangeHandler
+public sealed class Grid<T> : ChildCollectionView<Grid<T>, T>, IVisibilityChangeHandler
 {
     private readonly List<IView> _forceRerenderChildren = new();
     private readonly object _forceRerenderChildrenLock = new();
@@ -202,7 +202,8 @@ public sealed class Grid<T> : ChildContainerView<Grid<T>, T>, IVisibilityChangeH
         }
     }
 
-    private bool RenderViewsByPosition(RenderContext context,
+    private bool RenderViewsByPosition(
+        in RenderContext context,
         Position gridPosition,
         Size gridSize,
         ReadOnlySpan<int> columnWidths,
@@ -238,39 +239,26 @@ public sealed class Grid<T> : ChildContainerView<Grid<T>, T>, IVisibilityChangeH
 
         if (!viewsByPosition.TryGetValue((column, row), out var children))
         {
-            RenderEmpty(context, renderPosition, renderSize);
+            RenderEmpty(context, renderPosition, renderSize, false);
             return true;
         }
 
         var needsRerender = children.Any(forceRerenderChildren.Contains);
+        var updatedContext = context;
         if (needsRerender)
         {
-            context = new RenderContext(
+            updatedContext = context with {ForceRerender = true};
-                context.ConsoleDriver,
+            RenderEmpty(updatedContext, renderPosition, renderSize, false);
-                true,
-                context.Foreground,
-                context.Background,
-                context.Statistics,
-                context.TextFormat
-            );
-            RenderEmpty(context, renderPosition, renderSize);
         }
 
         //This implies that children further back in the list will be rendered on top of children placed before in the list.
-        foreach (var child in children.Where(child => child.IsVisible))
+        foreach (var child in children)
         {
-            var rendered = child.Render(context, renderPosition, renderSize);
+            var rendered = child.Render(updatedContext, renderPosition, renderSize);
             if (rendered && !needsRerender)
             {
                 needsRerender = true;
-                context = new RenderContext(
+                updatedContext = context with {ForceRerender = true};
-                    context.ConsoleDriver,
-                    true,
-                    context.Foreground,
-                    context.Background,
-                    context.Statistics,
-                    context.TextFormat
-                );
             }
         }
 

src/Library/TerminalUI/Controls/ItemsControl.cs

@@ -162,6 +162,8 @@ public sealed partial class ItemsControl<TDataContext, TItem>
                 ? childSize.Height
                 : childSize.Width;
         }
+        
+        // TODO: clean non used space
 
         return neededRerender;
     }

src/Library/TerminalUI/Controls/ListView.cs

@@ -232,6 +232,8 @@ public sealed partial class ListView<TDataContext, TItem> : View<ListView<TDataC
             item.Render(renderContext, position with {X = position.X + deltaX}, size with {Width = width});
             deltaX = nextDeltaX;
         }
+        
+        //TODO: render empty to remaining space
 
         return true;
     }
@@ -277,23 +279,20 @@ public sealed partial class ListView<TDataContext, TItem> : View<ListView<TDataC
         if (lastItemIndex > listViewItems.Length)
             lastItemIndex = listViewItems.Length;
 
+        var anyRendered = false;
         for (var i = renderStartIndex; i < lastItemIndex; i++)
         {
             var item = listViewItems[i];
-            item.Render(renderContext, position with {Y = position.Y + deltaY}, requestedItemSize with {Width = size.Width});
+            anyRendered = 
+                item.Render(renderContext, position with {Y = position.Y + deltaY}, requestedItemSize with {Width = size.Width}) 
+                || anyRendered;
             deltaY += requestedItemSize.Height;
         }
 
-        var driver = ApplicationContext!.ConsoleDriver;
+        // TODO: this should only render if deltaY is changed compared to last render or if last render was a horizontal
-        var placeholder = new string(' ', size.Width);
+        RenderEmpty(renderContext, position with {Y = position.Y + deltaY}, size with {Height = size.Height - deltaY}, false);
-        driver.ResetStyle();
-        for (var i = deltaY; i < size.Height; i++)
-        {
-            driver.SetCursorPosition(position with {Y = position.Y + i});
-            driver.Write(placeholder);
-        }
 
-        return true;
+        return anyRendered;
     }
 
     private ReadOnlySpan<ListViewItem<TItem, TDataContext>> InstantiateItemViews()

src/Library/TerminalUI/Controls/ProgressBar.cs

@@ -67,7 +67,7 @@ public partial class ProgressBar<T> : View<ProgressBar<T>, T>
             unfilledForeground,
             unfilledBackground);
 
-        if (!renderContext.ForceRerender && !NeedsRerender(renderState)) return false;
+        var skipRender = !renderContext.ForceRerender && !NeedsRerender(renderState);
 
         var utf8Support = ApplicationContext!.SupportUtf8Output;
         var unfilledCharacter = unfilledCharacterS.GetChar(utf8Support);
@@ -117,16 +117,17 @@ public partial class ProgressBar<T> : View<ProgressBar<T>, T>
         var textStartPosition = position;
         if (leftCap.HasValue)
         {
-            RenderText(leftCap.Value, driver, position, size with {Width = 1});
+            RenderText(leftCap.Value, renderContext, position, size with {Width = 1}, skipRender);
             textStartPosition = textStartPosition with {X = textStartPosition.X + 1};
         }
 
         // Filled
         RenderText(
             filledText,
-            driver,
+            renderContext,
             textStartPosition,
-            size with {Width = progressQuotientWidth}
+            size with {Width = progressQuotientWidth}, 
+            skipRender
         );
 
         // Transient character
@@ -135,9 +136,10 @@ public partial class ProgressBar<T> : View<ProgressBar<T>, T>
             SetStyleColor(renderContext, foreground, unfilledBackground);
             RenderText(
                 transientChar,
-                driver,
+                renderContext,
                 textStartPosition with {X = textStartPosition.X + progressQuotientWidth},
-                size with {Width = 1}
+                size with {Width = 1},
+                skipRender
             );
         }
 
@@ -150,9 +152,10 @@ public partial class ProgressBar<T> : View<ProgressBar<T>, T>
             SetStyleColor(renderContext, unfilledForeground, unfilledBackground);
             RenderText(
                 unfilledText,
-                driver,
+                renderContext,
                 textStartPosition with {X = textStartPosition.X + progressQuotientWidth + 1},
-                size with {Width = progressRemainderWidth}
+                size with {Width = progressRemainderWidth},
+                skipRender
             );
         }
 
@@ -162,12 +165,13 @@ public partial class ProgressBar<T> : View<ProgressBar<T>, T>
             SetStyleColor(renderContext, foreground, background);
             RenderText(
                 rightCap.Value,
-                driver,
+                renderContext,
                 position with {X = position.X + size.Width - 1},
-                size with {Width = 1});
+                size with {Width = 1},
+                skipRender);
         }
 
-        return true;
+        return !skipRender;
     }
 
     private bool NeedsRerender(RenderState renderState)

src/Library/TerminalUI/Controls/Rectangle.cs

@@ -13,32 +13,40 @@ public sealed partial class Rectangle<T> : View<Rectangle<T>, T>, IDisplayView
         IColor? Color);
 
     private RenderState? _lastRenderState;
+
+    [Notify] private IColor? _fill;
+
+    public Rectangle()
+    {
+        RerenderProperties.Add(nameof(Fill));
+    }
+
     protected override Size CalculateSize() => new(Width ?? 0, Height ?? 0);
 
     protected override bool DefaultRenderer(in RenderContext renderContext, Position position, Size size)
     {
-        var color = Background ?? renderContext.Background;
+        var fillColor = Fill ?? Background ?? renderContext.Background;
-        var renderState = new RenderState(position, size, color);
+        var renderState = new RenderState(position, size, fillColor);
-        if (!renderContext.ForceRerender && !NeedsRerender(renderState)) return false;
+        var skipRender = !renderContext.ForceRerender && !NeedsRerender(renderState);
         _lastRenderState = renderState;
 
         var driver = renderContext.ConsoleDriver;
 
-        var s = new string(' ', size.Width);
         driver.ResetStyle();
-        if (color is not null)
+        if (fillColor is not null)
         {
-            driver.SetBackgroundColor(color);
+            driver.SetBackgroundColor(fillColor);
         }
 
-        var height = size.Height;
+        RenderEmpty(
-        for (var i = 0; i < height; i++)
+            renderContext,
-        {
+            position,
-            driver.SetCursorPosition(position with {Y = position.Y + i});
+            size,
-            driver.Write(s);
+            skipRender,
-        }
+            false
+        );
 
-        return true;
+        return !skipRender;
     }
 
     private bool NeedsRerender(RenderState renderState)

src/Library/TerminalUI/Controls/StackPanel.cs

@@ -4,7 +4,7 @@ using TerminalUI.Traits;
 
 namespace TerminalUI.Controls;
 
-public sealed partial class StackPanel<T> : ChildContainerView<StackPanel<T>, T>, IVisibilityChangeHandler
+public sealed partial class StackPanel<T> : ChildCollectionView<StackPanel<T>, T>, IVisibilityChangeHandler
 {
     private readonly List<IView> _forceRerenderChildren = new();
     private readonly object _forceRerenderChildrenLock = new();
@@ -39,7 +39,10 @@ public sealed partial class StackPanel<T> : ChildContainerView<StackPanel<T>, T>
         return new Size(width, height);
     }
 
-    protected override bool DefaultRenderer(in RenderContext renderContext, Position position, Size size)
+    protected override bool DefaultRenderer(
+        in RenderContext renderContext,
+        Position position,
+        Size size)
     {
         var neededRerender = false;
         IReadOnlyList<IView> forceRerenderChildren;
@@ -102,9 +105,10 @@ public sealed partial class StackPanel<T> : ChildContainerView<StackPanel<T>, T>
             SetColorsForDriver(renderContext);
             RenderText(
                 text,
-                renderContext.ConsoleDriver,
+                renderContext,
                 position with {X = position.X + delta},
-                size with {Width = leftWidth}
+                size with {Width = leftWidth},
+                !neededRerender
             );
         }
         else
@@ -116,9 +120,10 @@ public sealed partial class StackPanel<T> : ChildContainerView<StackPanel<T>, T>
             SetColorsForDriver(renderContext);
             RenderText(
                 text,
-                renderContext.ConsoleDriver,
+                renderContext,
                 position with {Y = position.Y + delta},
-                size with {Height = leftHeight}
+                size with {Height = leftHeight},
+                !neededRerender
             );
         }
 

src/Library/TerminalUI/Controls/TextBlock.cs

@@ -58,7 +58,7 @@ public sealed partial class TextBlock<T> : View<TextBlock<T>, T>, IDisplayView
             background,
             _textFormat);
 
-        if (!renderContext.ForceRerender && !NeedsRerender(renderState)) return false;
+        var skipRender = !renderContext.ForceRerender && !NeedsRerender(renderState);
 
         _lastRenderState = renderState;
 
@@ -67,7 +67,7 @@ public sealed partial class TextBlock<T> : View<TextBlock<T>, T>, IDisplayView
             if (_placeholderRenderDone)
             {
                 _placeholderRenderDone = true;
-                RenderEmpty(renderContext, position, size);
+                RenderEmpty(renderContext, position, size, skipRender);
             }
 
             return false;
@@ -75,12 +75,11 @@ public sealed partial class TextBlock<T> : View<TextBlock<T>, T>, IDisplayView
 
         _placeholderRenderDone = false;
 
-        var driver = renderContext.ConsoleDriver;
         SetStyleColor(renderContext, foreground, background, _textFormat);
 
-        RenderText(_textLines, driver, position, size, TransformText);
+        RenderText(_textLines, renderContext, position, size, skipRender, TransformText);
 
-        return true;
+        return !skipRender;
     }
 
     private string TransformText(string text, Position position, Size size)

src/Library/TerminalUI/Controls/TextBox.cs

@@ -100,38 +100,39 @@ public sealed partial class TextBox<T> : View<TextBox<T>, T>, IFocusable, IDispl
             foreground,
             background);
 
-        if (!renderContext.ForceRerender && !NeedsRerender(renderStatus)) return false;
+        var skipRender = !renderContext.ForceRerender && !NeedsRerender(renderStatus);
         _lastRenderState = renderStatus;
 
         var driver = renderContext.ConsoleDriver;
         SetStyleColor(renderContext, foreground, background);
 
-        RenderEmpty(renderContext, position, size);
+        RenderEmpty(renderContext, position, size, skipRender);
 
         if (PasswordChar is { } passwordChar && !char.IsControl(passwordChar))
         {
             for (var i = 0; i < _textLines.Count; i++)
             {
                 var pos = position with {Y = position.Y + i};
-                RenderPasswordTextLine(_textLines[i], passwordChar, driver, pos, size);
+                RenderPasswordTextLine(_textLines[i], passwordChar, renderContext, pos, size, skipRender);
             }
         }
         else
         {
-            RenderText(_textLines, driver, position, size);
+            RenderText(_textLines, renderContext, position, size, skipRender);
         }
 
         _cursorPosition = position + _relativeCursorPosition;
 
-        return true;
+        return !skipRender;
     }
 
     private void RenderPasswordTextLine(
         string sourceText,
         char passwordChar,
-        IConsoleDriver driver,
+        in RenderContext renderContext,
         Position position,
-        Size size)
+        Size size,
+        bool updateCellsOnly)
     {
         Span<char> text = stackalloc char[sourceText.Length];
         for (var j = 0; j < text.Length; j++)
@@ -139,7 +140,7 @@ public sealed partial class TextBox<T> : View<TextBox<T>, T>, IFocusable, IDispl
             text[j] = passwordChar;
         }
 
-        RenderText(text, driver, position, size);
+        RenderText(text, renderContext, position, size, updateCellsOnly);
     }
 
     private bool NeedsRerender(RenderState renderState)

src/Library/TerminalUI/Controls/View.cs

@@ -6,7 +6,6 @@ using System.Runtime.CompilerServices;
 using GeneralInputKey;
 using PropertyChanged.SourceGenerator;
 using TerminalUI.Color;
-using TerminalUI.ConsoleDrivers;
 using TerminalUI.Models;
 using TerminalUI.TextFormat;
 using TerminalUI.Traits;
@@ -200,12 +199,18 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
         return renderResult;
     }
 
-    protected void RenderEmpty(in RenderContext renderContext, Position position, Size size)
+    protected void RenderEmpty(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly, bool resetStyle = true)
     {
+        UpdateCells(renderContext.UpdatedCells, position, size.Width, size.Height);
+        if (updateCellsOnly) return;
         var driver = renderContext.ConsoleDriver;
-        driver.ResetStyle();
+        if (resetStyle)
+        {
+            driver.ResetStyle();
+        }
 
-        var placeHolder = new string(ApplicationContext!.EmptyCharacter, size.Width);
+        Span<char> placeHolder = stackalloc char[size.Width];
+        placeHolder.Fill(ApplicationContext!.EmptyCharacter);
         for (var i = 0; i < size.Height; i++)
         {
             driver.SetCursorPosition(position with {Y = position.Y + i});
@@ -213,13 +218,30 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
         }
     }
 
+    private void UpdateCells(bool[,] renderContextUpdatedCells, Position position, int sizeWidth, int sizeHeight)
+    {
+        for (var x = 0; x < sizeWidth; x++)
+        {
+            for (var y = 0; y < sizeHeight; y++)
+            {
+                renderContextUpdatedCells[position.X + x, position.Y + y] = true;
+            }
+        }
+    }
+
     protected void RenderText(
         IList<string> textLines,
-        IConsoleDriver driver,
+        in RenderContext renderContext,
         Position position,
         Size size,
+        bool updateCellsOnly,
         TextTransformer? textTransformer = null)
     {
+        UpdateCells(renderContext.UpdatedCells, position, size.Width, size.Height);
+
+        if (updateCellsOnly) return;
+
+        var driver = renderContext.ConsoleDriver;
         for (var i = 0; i < textLines.Count; i++)
         {
             var currentPosition = position with {Y = position.Y + i};
@@ -234,6 +256,10 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
             {
                 text = text[..size.Width];
             }
+            else if (text.Length < size.Width)
+            {
+                text = text.PadRight(size.Width);
+            }
 
             try
             {
@@ -247,38 +273,17 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
     }
 
     protected void RenderText(
-        string text,
+        in ReadOnlySpan<char> text,
-        IConsoleDriver driver,
+        in RenderContext renderContext,
         Position position,
         Size size,
-        TextTransformer? textTransformer = null)
+        bool updateCellsOnly)
     {
-        for (var i = 0; i < size.Height; i++)
+        UpdateCells(renderContext.UpdatedCells, position, size.Width, size.Height);
-        {
-            var currentPosition = position with {Y = position.Y + i};
-            var finalText = text;
 
-            if (textTransformer is not null)
+        if (updateCellsOnly) return;
-            {
-                finalText = textTransformer(finalText, currentPosition, size);
-            }
 
-            if (finalText.Length > size.Width)
+        var driver = renderContext.ConsoleDriver;
-            {
-                finalText = finalText[..size.Width];
-            }
-
-            driver.SetCursorPosition(currentPosition);
-            driver.Write(finalText);
-        }
-    }
-
-    protected void RenderText(
-        in ReadOnlySpan<char> text,
-        IConsoleDriver driver,
-        Position position,
-        Size size)
-    {
         for (var i = 0; i < size.Height; i++)
         {
             var currentPosition = position with {Y = position.Y + i};
@@ -296,10 +301,16 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
 
     protected void RenderText(
         char content,
-        IConsoleDriver driver,
+        in RenderContext renderContext,
         Position position,
-        Size size)
+        Size size,
+        bool updateCellsOnly)
     {
+        UpdateCells(renderContext.UpdatedCells, position, size.Width, size.Height);
+
+        if (updateCellsOnly) return;
+
+        var driver = renderContext.ConsoleDriver;
         var contentString = new string(content, size.Width);
 
         for (var i = 0; i < size.Height; i++)
@@ -323,6 +334,7 @@ public abstract partial class View<TConcrete, T> : IView<T> where TConcrete : Vi
         {
             t.ApplyFormat(driver, renderContext.TextFormat);
         }
+
         if (foreground is not null)
         {
             driver.SetForegroundColor(foreground);

src/Library/TerminalUI/Models/RenderContext.cs

@@ -16,6 +16,7 @@ public readonly ref struct RenderContext
     public IColor? Background { get; init; }
     public RenderStatistics Statistics { get; init; }
     public TextFormatContext TextFormat { get; init; }
+    public bool[,] UpdatedCells { get; init; }
 
     public RenderContext(
         IConsoleDriver consoleDriver,
@@ -23,7 +24,8 @@ public readonly ref struct RenderContext
         IColor? foreground,
         IColor? background,
         RenderStatistics statistics,
-        TextFormatContext textFormat)
+        TextFormatContext textFormat,
+        bool[,] updatedCells)
     {
         RenderId = _renderId++;
 
@@ -33,6 +35,7 @@ public readonly ref struct RenderContext
         Background = background;
         Statistics = statistics;
         TextFormat = textFormat;
+        UpdatedCells = updatedCells;
     }
 
     public static RenderContext Empty =>
@@ -42,6 +45,7 @@ public readonly ref struct RenderContext
             null,
             null,
             new RenderStatistics(),
-            new TextFormatContext(false)
+            new TextFormatContext(false),
+            new bool[0, 0]
         );
 }

src/Library/TerminalUI/RenderEngine.cs

@@ -1,4 +1,5 @@
-using TerminalUI.Controls;
+using TerminalUI.ConsoleDrivers;
+using TerminalUI.Controls;
 using TerminalUI.Models;
 using TerminalUI.TextFormat;
 using TerminalUI.Traits;
@@ -14,6 +15,9 @@ public class RenderEngine : IRenderEngine
     private readonly List<IView> _forcedTemporaryViewsToRender = new();
     private bool _rerenderRequested = true;
     private bool _lastCursorVisible;
+    private bool[,]? _updatedCells;
+    private bool[,]? _filledCells;
+    private bool[,]? _lastFilledCells;
 
     public RenderEngine(IApplicationContext applicationContext, IEventLoop eventLoop)
     {
@@ -77,6 +81,18 @@ public class RenderEngine : IRenderEngine
         var initialPosition = new Position(0, 0);
         var size = driver.GetWindowSize();
 
+        //TODO: this could be stack allocated when sizes are small
+        if (_updatedCells is null
+            || _updatedCells.GetLength(0) != size.Width
+            || _updatedCells.GetLength(1) != size.Height)
+        {
+            _updatedCells = new bool[size.Width, size.Height];
+        }
+        else
+        {
+            ClearArray2D(_updatedCells);
+        }
+
         RenderViews(
             forcedTemporaryViewsToRender,
             new RenderContext(
@@ -85,7 +101,8 @@ public class RenderEngine : IRenderEngine
                 null,
                 null,
                 new RenderStatistics(),
-                new TextFormatContext(driver.SupportsAnsiEscapeSequence)
+                new TextFormatContext(driver.SupportsAnsiEscapeSequence),
+                _updatedCells
             ),
             initialPosition,
             size);
@@ -98,11 +115,41 @@ public class RenderEngine : IRenderEngine
                 null,
                 null,
                 new RenderStatistics(),
-                new TextFormatContext(driver.SupportsAnsiEscapeSequence)
+                new TextFormatContext(driver.SupportsAnsiEscapeSequence),
+                _updatedCells
             ),
             initialPosition,
             size);
 
+        if (_lastFilledCells is not null
+            && _lastFilledCells.GetLength(0) == size.Width
+            && _lastFilledCells.GetLength(1) == size.Height)
+        {
+            Array2DHelper.CombineArray2Ds(
+                _updatedCells,
+                _lastFilledCells,
+                new Position(0, 0),
+                _updatedCells,
+                (a, b) => (a ?? false) || (b ?? false)
+            );
+        }
+
+        if (_filledCells is null
+            || _filledCells.GetLength(0) != size.Width
+            || _filledCells.GetLength(1) != size.Height)
+        {
+            _filledCells = new bool[size.Width, size.Height];
+        }
+        else
+        {
+            ClearArray2D(_filledCells);
+        }
+
+        driver.ResetStyle();
+        Array2DHelper.RenderEmpty(driver, _updatedCells, _filledCells, _applicationContext.EmptyCharacter, initialPosition, size);
+
+        (_lastFilledCells, _filledCells) = (_filledCells, _lastFilledCells);
+
         if (_applicationContext.FocusManager.Focused is { } focused)
         {
             focused.SetCursorPosition(driver);
@@ -129,6 +176,20 @@ public class RenderEngine : IRenderEngine
         }
     }
 
+    private void ClearArray2D<T>(T[,] array, T defaultValue = default!)
+    {
+        var maxX = array.GetLength(0);
+        var maxY = array.GetLength(1);
+
+        for (var x = 0; x < maxX; x++)
+        {
+            for (var y = 0; y < maxY; y++)
+            {
+                array[x, y] = defaultValue;
+            }
+        }
+    }
+
     public void AddViewToPermanentRenderGroup(IView view)
     {
         lock (_lock)