Rework how TextBlock skips redundant measure and arrange calls (#17271)

* Rework how TextBlock skips redundant measure and arrange calls
Add some tests

* Adjust tests

* Try this

* Make sure the TextBlock is arranged after it has been measured with a different availableSize

* Make it more clear that we are resetting and recreating the TextLayout

* Capture textLayout after inlines have been processed

src/Avalonia.Controls/TextBlock.cs

@@ -162,7 +162,7 @@ public class TextBlock : Control, IInlineHost
                 nameof(Inlines), t => t.Inlines, (t, v) => t.Inlines = v);
 
         private TextLayout? _textLayout;
-        protected Size _constraint;
+        protected Size _constraint = Size.Infinity;
         protected IReadOnlyList<TextRun>? _textRuns;
         private InlineCollection? _inlines;
 
@@ -701,13 +701,19 @@ protected override Size MeasureOverride(Size availableSize)
         {
             var scale = LayoutHelper.GetLayoutScale(this);
             var padding = LayoutHelper.RoundLayoutThickness(Padding, scale, scale);
+            var deflatedSize = availableSize.Deflate(padding);
 
-            _constraint = availableSize.Deflate(padding);
-
-            //Reset TextLayout otherwise constraint might be outdated.
-            _textLayout?.Dispose();
-            _textLayout = null;
+            if(_constraint != deflatedSize)
+            {
+                //Reset TextLayout when the constraint is not matching.
+                _textLayout?.Dispose();
+                _textLayout = null;
+                _constraint = deflatedSize;
 
+                //Force arrange so text will be properly alligned.
+                InvalidateArrange();
+            }
+
             var inlines = Inlines;
 
             if (HasComplexContent)
@@ -722,29 +728,41 @@ protected override Size MeasureOverride(Size availableSize)
                 _textRuns = textRuns;
             }
 
-            var width = TextLayout.OverhangLeading + TextLayout.WidthIncludingTrailingWhitespace + TextLayout.OverhangTrailing;
+            //This implicitly recreated the TextLayout with a new constraint if we previously reset it.
+            var textLayout = TextLayout;
+
+            var width = textLayout.OverhangLeading + textLayout.WidthIncludingTrailingWhitespace + textLayout.OverhangTrailing;
+
+            var size = LayoutHelper.RoundLayoutSizeUp(new Size(width, textLayout.Height).Inflate(padding), 1, 1);   
 
-            return new Size(width, TextLayout.Height).Inflate(padding);
+            _constraint = size;
+
+            return size;
         }
 
         protected override Size ArrangeOverride(Size finalSize)
         {
             var scale = LayoutHelper.GetLayoutScale(this);
             var padding = LayoutHelper.RoundLayoutThickness(Padding, scale, scale);
 
+            var availableSize = finalSize.Deflate(padding);
+
             //Fixes: #11019
-            if (finalSize.Width < _constraint.Width)
+            if (availableSize != _constraint)
             {
                 _textLayout?.Dispose();
                 _textLayout = null;
-                _constraint = finalSize.Deflate(padding);
+                _constraint = availableSize;
             }
 
+            //This implicitly recreated the TextLayout with a new constraint if we previously reset it.
+            var textLayout = TextLayout;
+
             if (HasComplexContent)
             {             
                 var currentY = padding.Top;
 
-                foreach (var textLine in TextLayout.TextLines)
+                foreach (var textLine in textLayout.TextLines)
                 {
                     var currentX = padding.Left + textLine.Start;
 

tests/Avalonia.Controls.UnitTests/TextBlockTests.cs

@@ -1,13 +1,9 @@
-using System;
 using Avalonia.Controls.Documents;
 using Avalonia.Controls.Templates;
 using Avalonia.Data;
-using Avalonia.Input;
+using Avalonia.Layout;
 using Avalonia.Media;
-using Avalonia.Metadata;
-using Avalonia.Rendering;
 using Avalonia.UnitTests;
-using Moq;
 using Xunit;
 
 namespace Avalonia.Controls.UnitTests
@@ -37,20 +33,74 @@ public void Calling_Measure_Should_Update_Constraint_And_TextLayout()
             {
                 var textBlock = new TestTextBlock { Text = "Hello World" };
 
+                Assert.Equal(Size.Infinity, textBlock.Constraint);
+
                 textBlock.Measure(new Size(100, 100));
 
                 var textLayout = textBlock.TextLayout;
 
-                Assert.Equal(new Size(100,100), textBlock.Constraint);
+                Assert.Equal(new Size(110, 10), textBlock.Constraint);
 
                 textBlock.Measure(new Size(50, 100));
 
-                Assert.Equal(new Size(50, 100), textBlock.Constraint);
+                Assert.NotEqual(textLayout, textBlock.TextLayout);
+            }
+        }
+
+        [Fact]
+        public void Calling_Arrange_With_Different_Size_Should_Update_Constraint_And_TextLayout()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var textBlock = new TestTextBlock { Text = "Hello World" };
+
+                textBlock.Measure(Size.Infinity);
+
+                var textLayout = textBlock.TextLayout;
+
+                var constraint = LayoutHelper.RoundLayoutSizeUp(new Size(textLayout.WidthIncludingTrailingWhitespace, textLayout.Height), 1, 1);
+
+                Assert.Equal(constraint, textBlock.Constraint);
+
+                textBlock.Arrange(new Rect(constraint));
+
+                Assert.Equal(constraint, textBlock.Constraint);
+
+                Assert.Equal(textLayout, textBlock.TextLayout);
+
+                textBlock.Measure(constraint);
+
+                Assert.Equal(textLayout, textBlock.TextLayout);
+
+                constraint += new Size(50, 0);
+
+                textBlock.Arrange(new Rect(constraint));
+
+                Assert.Equal(constraint, textBlock.Constraint);
 
                 Assert.NotEqual(textLayout, textBlock.TextLayout);
             }
         }
 
+        [Fact]
+        public void Calling_Measure_With_Infinite_Space_Should_Set_DesiredSize()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var textBlock = new TestTextBlock { Text = "Hello World" };
+
+                textBlock.Measure(new Size(double.PositiveInfinity, double.PositiveInfinity));
+
+                var textLayout = textBlock.TextLayout;
+
+                Assert.Equal(new Size(110, 10), textBlock.Constraint);
+
+                var constraint = LayoutHelper.RoundLayoutSizeUp(new Size(textLayout.WidthIncludingTrailingWhitespace, textLayout.Height), 1, 1);
+
+                Assert.Equal(constraint, textBlock.DesiredSize);
+            }
+        }
+
         [Fact]
         public void Changing_InlinesCollection_Should_Invalidate_Measure()
         {