RenderEmpty fixes

src/Library/TerminalUI/Controls/Border.cs

@@ -7,6 +7,24 @@ namespace TerminalUI.Controls;
 
 public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
 {
+    private record struct RenderState(
+        Position Position,
+        Size Size,
+        Thickness BorderThickness,
+        Thickness Padding,
+        char TopChar,
+        char LeftChar,
+        char RightChar,
+        char BottomChar,
+        char TopLeftChar,
+        char TopRightChar,
+        char BottomLeftChar,
+        char BottomRightChar,
+        IColor? Fill
+    );
+    
+    private RenderState _lastRenderState;
+    
     [Notify] private Thickness _borderThickness = 1;
     [Notify] private Thickness _padding = 0;
     [Notify] private char _topChar = '─';
@@ -59,6 +77,27 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
         var backgroundColor = Background ?? renderContext.Background;
         var foregroundColor = Foreground ?? renderContext.Foreground;
         var fillColor = Fill ?? Background ?? renderContext.Background;
+        
+        var renderState = new RenderState(
+            position,
+            size,
+            _borderThickness,
+            _padding,
+            _topChar,
+            _leftChar,
+            _rightChar,
+            _bottomChar,
+            _topLeftChar,
+            _topRightChar,
+            _bottomLeftChar,
+            _bottomRightChar,
+            fillColor
+        );
+        var skipBorderRender = !renderContext.ForceRerender && !NeedsRerender(renderState);
+        if (!skipBorderRender)
+        {
+            _lastRenderState = renderState;
+        }
 
         var childPosition = new Position(X: position.X + _borderThickness.Left, Y: position.Y + _borderThickness.Top);
         var childSize = new Size(
@@ -96,7 +135,7 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
             SetStyleColor(renderContext, foregroundColor, backgroundColor);
         }
 
-        var updateCellsOnly = !contentRendered;
+        var updateCellsOnly = !contentRendered || skipBorderRender;
         RenderTopBorder(renderContext, position, size, updateCellsOnly);
         RenderBottomBorder(renderContext, position, size, updateCellsOnly);
         RenderLeftBorder(renderContext, position, size, updateCellsOnly);
@@ -110,7 +149,7 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
         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,
@@ -120,20 +159,22 @@ public sealed partial class Border<T> : ContentView<Border<T>, T>, IDisplayView
                 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)
-            );
         }
 
+        //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 bool NeedsRerender(RenderState renderState) => renderState != _lastRenderState;
+
     private void RenderTopBorder(in RenderContext renderContext, Position position, Size size, bool updateCellsOnly)
     {
         position = position with {X = position.X + _borderThickness.Left};

src/Library/TerminalUI/Controls/ContentView.cs

@@ -44,11 +44,10 @@ public abstract partial class ContentView<TConcrete, T>
 
     private bool DefaultContentRender(in RenderContext renderContext, Position position, Size size)
     {
-        if (Content is null || !Content.IsVisible)
+        if (Content is null)
         {
             if (_placeholderRenderDone) return false;
             _placeholderRenderDone = true;
-            RenderEmpty(renderContext, position, size, false);
             return true;
         }
 

src/Library/TerminalUI/Controls/Grid.cs

@@ -239,8 +239,7 @@ public sealed class Grid<T> : ChildCollectionView<Grid<T>, T>, IVisibilityChange
 
         if (!viewsByPosition.TryGetValue((column, row), out var children))
         {
-            RenderEmpty(context, renderPosition, renderSize, false);
-            return true;
+            return false;
         }
 
         var needsRerender = children.Any(forceRerenderChildren.Contains);
@@ -248,7 +247,6 @@ public sealed class Grid<T> : ChildCollectionView<Grid<T>, T>, IVisibilityChange
         if (needsRerender)
         {
             updatedContext = context with {ForceRerender = true};
-            RenderEmpty(updatedContext, renderPosition, renderSize, false);
         }
 
         //This implies that children further back in the list will be rendered on top of children placed before in the list.

src/Library/TerminalUI/Controls/ListView.cs

@@ -218,6 +218,7 @@ public sealed partial class ListView<TDataContext, TItem> : View<ListView<TDataC
         }
 
         var deltaX = 0;
+        var anyRendered = false;
         for (var i = renderStartIndex; i < _listViewItemLength; i++)
         {
             var item = listViewItems[i];
@@ -229,13 +230,13 @@ public sealed partial class ListView<TDataContext, TItem> : View<ListView<TDataC
                 width = size.Width - deltaX;
             }
 
-            item.Render(renderContext, position with {X = position.X + deltaX}, size with {Width = width});
+            anyRendered =
+                item.Render(renderContext, position with {X = position.X + deltaX}, size with {Width = width})
+                || anyRendered;
             deltaX = nextDeltaX;
         }
-        
-        //TODO: render empty to remaining space
 
-        return true;
+        return anyRendered;
     }
 
     private bool RenderVertical(in RenderContext renderContext, Position position, Size size)
@@ -283,15 +284,12 @@ public sealed partial class ListView<TDataContext, TItem> : View<ListView<TDataC
         for (var i = renderStartIndex; i < lastItemIndex; i++)
         {
             var item = listViewItems[i];
-            anyRendered = 
-                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;
         }
 
-        // TODO: this should only render if deltaY is changed compared to last render or if last render was a horizontal
-        RenderEmpty(renderContext, position with {Y = position.Y + deltaY}, size with {Height = size.Height - deltaY}, false);
-
         return anyRendered;
     }
 

src/Library/TerminalUI/Controls/TextBlock.cs

@@ -64,10 +64,11 @@ public sealed partial class TextBlock<T> : View<TextBlock<T>, T>, IDisplayView
 
         if (_textLines is null)
         {
-            if (_placeholderRenderDone)
+            if (!_placeholderRenderDone)
             {
                 _placeholderRenderDone = true;
                 RenderEmpty(renderContext, position, size, skipRender);
+                return true;
             }
 
             return false;

src/Library/TerminalUI/RenderEngine.cs

@@ -146,7 +146,13 @@ public class RenderEngine : IRenderEngine
         }
 
         driver.ResetStyle();
-        Array2DHelper.RenderEmpty(driver, _updatedCells, _filledCells, _applicationContext.EmptyCharacter, initialPosition, size);
+        Array2DHelper.RenderEmpty(
+            driver,
+            _updatedCells,
+            _filledCells,
+            _applicationContext.EmptyCharacter,
+            initialPosition,
+            size);
 
         (_lastFilledCells, _filledCells) = (_filledCells, _lastFilledCells);