Implement ItemSpacing and LineSpacing in ElasticWrapPanel (#843)

* Initial plan

* Implement ItemSpacing and LineSpacing support for ElasticWrapPanel

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* Add demo tab showcasing ItemSpacing and LineSpacing

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* Add additional test for ItemSpacing affecting line wrapping

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* feat: add bindings for IsFillHorizontal and IsFillVertical in ElasticWrapPanelDemo

* Fix measure/arrange mismatch by tracking spacing in UVCollection

Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>

* feat: add ItemSpacing & LineSpacing FormItems.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: rabbitism <14807942+rabbitism@users.noreply.github.com>
Co-authored-by: Dong Bin <popmessiah@hotmail.com>
Co-authored-by: Zhang Dian <54255897+zdpcdt@users.noreply.github.com>

demo/Ursa.Demo/Pages/ElasticWrapPanelDemo.axaml

@@ -64,6 +64,22 @@
                         Minimum="0"
                         Value="{Binding ItemHeight}" />
                 </u:FormItem>
+                <u:FormItem Label="ItemSpacing">
+                    <u:NumericDoubleUpDown
+                        AllowDrag="True"
+                        Step="1"
+                        Maximum="100"
+                        Minimum="-10"
+                        Value="{Binding ItemSpacing}" />
+                </u:FormItem>
+                <u:FormItem Label="LineSpacing">
+                    <u:NumericDoubleUpDown
+                        AllowDrag="True"
+                        Step="1"
+                        Maximum="100"
+                        Minimum="-10"
+                        Value="{Binding LineSpacing}" />
+                </u:FormItem>
             </u:FormGroup>
             <u:FormGroup Header="FixToRB Extension" IsEnabled="{Binding #FixToRBTabItem.IsSelected}">
                 <u:FormItem>
@@ -108,6 +124,8 @@
                                             IsFillVertical="{Binding IsFillVertical}"
                                             ItemHeight="{Binding ItemHeight}"
                                             ItemWidth="{Binding ItemWidth}"
+                                            ItemSpacing="{Binding ItemSpacing}"
+                                            LineSpacing="{Binding LineSpacing}"
                                             Orientation="{Binding SelectedOrientation}">
                             <Border Background="{DynamicResource SemiRed5Color}" />
                             <Border Background="{DynamicResource SemiPink5Color}" />
@@ -134,6 +152,8 @@
                                                 IsFillVertical="{Binding IsFillVertical}"
                                                 ItemHeight="{Binding ItemHeight}"
                                                 ItemWidth="{Binding ItemWidth}"
+                                                ItemSpacing="{Binding ItemSpacing}"
+                                                LineSpacing="{Binding LineSpacing}"
                                                 Orientation="{Binding SelectedOrientation}">
                                 <Border Background="{DynamicResource SemiRed5Color}" />
                                 <Border Background="{DynamicResource SemiPink5Color}" />
@@ -165,6 +185,8 @@
                                                     IsFillVertical="{Binding IsFillVertical}"
                                                     ItemHeight="{Binding ItemHeight}"
                                                     ItemWidth="{Binding ItemWidth}"
+                                                    ItemSpacing="{Binding ItemSpacing}"
+                                                    LineSpacing="{Binding LineSpacing}"
                                                     Orientation="{Binding SelectedOrientation}">
                                     <Border Background="{DynamicResource SemiRed5Color}" />
                                     <Border Background="{DynamicResource SemiPink5Color}" />
@@ -200,6 +222,8 @@
                                         <u:Divider HorizontalContentAlignment="Left" Content="WrapPanel" />
                                         <WrapPanel ItemHeight="{Binding ItemHeight}"
                                                    ItemWidth="{Binding ItemWidth}"
+                                                   ItemSpacing="{Binding ItemSpacing}"
+                                                   LineSpacing="{Binding LineSpacing}"
                                                    Orientation="{Binding SelectedOrientation}">
                                             <Border Background="{DynamicResource SemiRed5Color}" />
                                             <Border Background="{DynamicResource SemiPink5Color}" />
@@ -223,6 +247,8 @@
                                                             IsFillVertical="{Binding IsFillVertical}"
                                                             ItemHeight="{Binding ItemHeight}"
                                                             ItemWidth="{Binding ItemWidth}"
+                                                            ItemSpacing="{Binding ItemSpacing}"
+                                                            LineSpacing="{Binding LineSpacing}"
                                                             Orientation="{Binding SelectedOrientation}">
                                             <Border Background="{DynamicResource SemiRed5Color}" />
                                             <Border Background="{DynamicResource SemiPink5Color}" />
@@ -249,6 +275,8 @@
                                         <u:Divider HorizontalContentAlignment="Left" Content="WrapPanel" />
                                         <WrapPanel ItemHeight="{Binding ItemHeight}"
                                                    ItemWidth="{Binding ItemWidth}"
+                                                   ItemSpacing="{Binding ItemSpacing}"
+                                                   LineSpacing="{Binding LineSpacing}"
                                                    Orientation="{Binding SelectedOrientation}">
                                             <Border Background="{DynamicResource SemiRed5Color}" />
                                             <Border Background="{DynamicResource SemiPink5Color}" />
@@ -285,6 +313,8 @@
                                                             IsFillVertical="{Binding IsFillVertical}"
                                                             ItemHeight="{Binding ItemHeight}"
                                                             ItemWidth="{Binding ItemWidth}"
+                                                            ItemSpacing="{Binding ItemSpacing}"
+                                                            LineSpacing="{Binding LineSpacing}"
                                                             Orientation="{Binding SelectedOrientation}">
                                             <Border Background="{DynamicResource SemiRed5Color}" />
                                             <Border Background="{DynamicResource SemiPink5Color}" />

demo/Ursa.Demo/ViewModels/ElasticWrapPanelDemoViewModel.cs

@@ -14,6 +14,8 @@ public partial class ElasticWrapPanelDemoViewModel : ObservableObject
     [ObservableProperty] private bool _isFillVertical;
     [ObservableProperty] private double _itemWidth = 40d;
     [ObservableProperty] private double _itemHeight = 40d;
+    [ObservableProperty] private double _itemSpacing;
+    [ObservableProperty] private double _lineSpacing;
 
     [ObservableProperty] private bool _autoWidth = true;
     [ObservableProperty] private bool _autoHeight = true;

src/Ursa/Controls/Panels/ElasticWrapPanel.cs

@@ -12,8 +12,8 @@ public class ElasticWrapPanel : WrapPanel
 {
     static ElasticWrapPanel()
     {
-        AffectsMeasure<ElasticWrapPanel>(IsFillHorizontalProperty, IsFillVerticalProperty);
+        AffectsMeasure<ElasticWrapPanel>(IsFillHorizontalProperty, IsFillVerticalProperty, ItemSpacingProperty, LineSpacingProperty);
-        AffectsArrange<ElasticWrapPanel>(IsFillHorizontalProperty, IsFillVerticalProperty);
+        AffectsArrange<ElasticWrapPanel>(IsFillHorizontalProperty, IsFillVerticalProperty, ItemSpacingProperty, LineSpacingProperty);
     }
 
     #region AttachedProperty
@@ -78,6 +78,8 @@ public class ElasticWrapPanel : WrapPanel
         double itemHeight = ItemHeight;
         var orientation = Orientation;
         var children = Children;
+        double itemSpacing = ItemSpacing;
+        double lineSpacing = LineSpacing;
 
         // Determine the space required for items in the same row/column based on horizontal/vertical arrangement
         var curLineSize = new UVSize(orientation);
@@ -111,6 +113,8 @@ public class ElasticWrapPanel : WrapPanel
             itemWidthSet ? itemWidth : 0,
             itemHeightSet ? itemHeight : 0);
 
+        bool isFirstItemInLine = true;
+
         foreach (var child in children)
         {
             UVSize sz;
@@ -138,21 +142,38 @@ public class ElasticWrapPanel : WrapPanel
                     sz.V = itemSetSize.V;
                 }
 
-                if (MathHelpers.GreaterThan(curLineSize.U + sz.U, uvConstraint.U))
+                double itemUWithSpacing = isFirstItemInLine ? sz.U : sz.U + itemSpacing;
+                
+                if (MathHelpers.GreaterThan(curLineSize.U + itemUWithSpacing, uvConstraint.U))
                 {
                     panelSize.U = Max(curLineSize.U, panelSize.U);
+                    if (panelSize.V > 0)
+                    {
+                        panelSize.V += lineSpacing;
+                    }
                     panelSize.V += curLineSize.V;
                     curLineSize = sz;
+                    isFirstItemInLine = false;
                 }
                 else
                 {
+                    if (!isFirstItemInLine)
+                    {
+                        curLineSize.U += itemSpacing;
+                    }
                     curLineSize.U += sz.U;
                     curLineSize.V = Max(sz.V, curLineSize.V);
                     panelSize.U = Max(curLineSize.U, panelSize.U);
+                    if (panelSize.V > 0)
+                    {
+                        panelSize.V += lineSpacing;
+                    }
                     panelSize.V += curLineSize.V;
+                    isFirstItemInLine = false;
                 }
 
                 curLineSize = new UVSize(orientation);
+                isFirstItemInLine = true;
             }
             else
             {
@@ -164,23 +185,40 @@ public class ElasticWrapPanel : WrapPanel
                     itemWidthSet ? itemWidth : child.DesiredSize.Width,
                     itemHeightSet ? itemHeight : child.DesiredSize.Height);
 
-                if (MathHelpers.GreaterThan(curLineSize.U + sz.U, uvConstraint.U)) // Need to switch to another line
+                double itemUWithSpacing = isFirstItemInLine ? sz.U : sz.U + itemSpacing;
+
+                if (MathHelpers.GreaterThan(curLineSize.U + itemUWithSpacing, uvConstraint.U)) // Need to switch to another line
                 {
                     panelSize.U = Max(curLineSize.U, panelSize.U);
+                    if (panelSize.V > 0)
+                    {
+                        panelSize.V += lineSpacing;
+                    }
                     panelSize.V += curLineSize.V;
                     curLineSize = sz;
+                    isFirstItemInLine = false;
 
                     if (MathHelpers.GreaterThan(sz.U, uvConstraint.U)) // The element is wider than the constraint - give it a separate line
                     {
                         panelSize.U = Max(sz.U, panelSize.U);
+                        if (panelSize.V > 0)
+                        {
+                            panelSize.V += lineSpacing;
+                        }
                         panelSize.V += sz.V;
                         curLineSize = new UVSize(orientation);
+                        isFirstItemInLine = true;
                     }
                 }
                 else // Continue to accumulate a line
                 {
+                    if (!isFirstItemInLine)
+                    {
+                        curLineSize.U += itemSpacing;
+                    }
                     curLineSize.U += sz.U;
                     curLineSize.V = Max(sz.V, curLineSize.V);
+                    isFirstItemInLine = false;
                 }
             }
         }
@@ -197,6 +235,8 @@ public class ElasticWrapPanel : WrapPanel
     {
         bool itemWidthSet = !double.IsNaN(ItemWidth);
         bool itemHeightSet = !double.IsNaN(ItemHeight);
+        double itemSpacing = ItemSpacing;
+        double lineSpacing = LineSpacing;
 
         // This is the size for non-space measurement
         UVSize itemSetSize = new UVSize(Orientation,
@@ -212,7 +252,7 @@ public class ElasticWrapPanel : WrapPanel
         #region Get the collection of elements in the same direction
 
         // Current collection of elements in a row/column
-        UVCollection curLineUIs = new UVCollection(Orientation, itemSetSize);
+        UVCollection curLineUIs = new UVCollection(Orientation, itemSetSize, itemSpacing);
 
         // Iterate over the child elements
         var children = Children;
@@ -242,14 +282,16 @@ public class ElasticWrapPanel : WrapPanel
                     sz.V = itemSetSize.V;
                 }
 
-                if (MathHelpers.GreaterThan(curLineUIs.TotalU + sz.U, uvFinalSize.U))
+                // Account for spacing before this item if it's not the first
+                double spacingBeforeItem = curLineUIs.Count > 0 ? itemSpacing : 0;
+                if (MathHelpers.GreaterThan(curLineUIs.TotalU + spacingBeforeItem + sz.U, uvFinalSize.U))
                 {
                     if (curLineUIs.Count > 0)
                     {
                         lineUVCollection.Add(curLineUIs);
                     }
 
-                    curLineUIs = new UVCollection(Orientation, itemSetSize);
+                    curLineUIs = new UVCollection(Orientation, itemSetSize, itemSpacing);
                     curLineUIs.Add(child, sz, Convert.ToInt32(lengthCount));
                 }
                 else
@@ -258,7 +300,7 @@ public class ElasticWrapPanel : WrapPanel
                 }
 
                 lineUVCollection.Add(curLineUIs);
-                curLineUIs = new UVCollection(Orientation, itemSetSize);
+                curLineUIs = new UVCollection(Orientation, itemSetSize, itemSpacing);
             }
             else
             {
@@ -266,19 +308,21 @@ public class ElasticWrapPanel : WrapPanel
                     itemWidthSet ? ItemWidth : child.DesiredSize.Width,
                     itemHeightSet ? ItemHeight : child.DesiredSize.Height);
 
-                if (MathHelpers.GreaterThan(curLineUIs.TotalU + sz.U, uvFinalSize.U)) // Need to switch to another line
+                // Account for spacing before this item if it's not the first
+                double spacingBeforeItem = curLineUIs.Count > 0 ? itemSpacing : 0;
+                if (MathHelpers.GreaterThan(curLineUIs.TotalU + spacingBeforeItem + sz.U, uvFinalSize.U)) // Need to switch to another line
                 {
                     if (curLineUIs.Count > 0)
                     {
                         lineUVCollection.Add(curLineUIs);
                     }
 
-                    curLineUIs = new UVCollection(Orientation, itemSetSize);
+                    curLineUIs = new UVCollection(Orientation, itemSetSize, itemSpacing);
                     curLineUIs.Add(child, sz);
                     if (MathHelpers.GreaterThan(sz.U, uvFinalSize.U))
                     {
                         lineUVCollection.Add(curLineUIs);
-                        curLineUIs = new UVCollection(Orientation, itemSetSize);
+                        curLineUIs = new UVCollection(Orientation, itemSetSize, itemSpacing);
                     }
                 }
                 else
@@ -332,7 +376,8 @@ public class ElasticWrapPanel : WrapPanel
                         }
                         maxElementCount = Max(sum, maxElementCount);
                     }
-                    adaptULength = (uvFinalSize.U - maxElementCount * itemSetSize.U) / maxElementCount;
+                    double totalItemSpacing = maxElementCount > 1 ? (maxElementCount - 1) * itemSpacing : 0;
+                    adaptULength = (uvFinalSize.U - maxElementCount * itemSetSize.U - totalItemSpacing) / maxElementCount;
                     adaptULength = Max(adaptULength, 0);
                 }
             }
@@ -342,16 +387,19 @@ public class ElasticWrapPanel : WrapPanel
                 if (itemSetSize.V > 0)
                 {
                     isAdaptV = true;
-                    adaptVLength = uvFinalSize.V / lineUVCollection.Count;
+                    double totalLineSpacing = lineUVCollection.Count > 1 ? (lineUVCollection.Count - 1) * lineSpacing : 0;
+                    adaptVLength = (uvFinalSize.V - totalLineSpacing) / lineUVCollection.Count;
                 }
             }
 
             bool isHorizontal = Orientation == Orientation.Horizontal;
+            int lineIndex = 0;
             foreach (var uvCollection in lineUVCollection)
             {
                 double u = 0;
                 var lineUIEles = uvCollection.UICollection.Keys.ToList();
                 double linevV = isAdaptV ? adaptVLength : uvCollection.LineV;
+                int itemIndex = 0;
                 foreach (var child in lineUIEles)
                 {
                     UVLengthSize childSize = uvCollection.UICollection[child];
@@ -384,9 +432,19 @@ public class ElasticWrapPanel : WrapPanel
                     }
 
                     u += layoutSlotU;
+                    if (itemIndex < lineUIEles.Count - 1)
+                    {
+                        u += itemSpacing;
+                    }
+                    itemIndex++;
                 }
 
                 accumulatedV += linevV;
+                if (lineIndex < lineUVCollection.Count - 1)
+                {
+                    accumulatedV += lineSpacing;
+                }
+                lineIndex++;
                 lineUIEles.Clear();
             }
         }
@@ -463,14 +521,25 @@ public class ElasticWrapPanel : WrapPanel
 
         private UVSize ItemSetSize;
         
-        public UVCollection(Orientation orientation, UVSize itemSetSize)
+        private double ItemSpacing;
+
+        public UVCollection(Orientation orientation, UVSize itemSetSize, double itemSpacing = 0)
         {
             UICollection = new Dictionary<Control, UVLengthSize>();
             LineDesireUVSize = new UVSize(orientation);
             ItemSetSize = itemSetSize;
+            ItemSpacing = itemSpacing;
         }
 
-        public double TotalU => LineDesireUVSize.U;
+        public double TotalU
+        {
+            get
+            {
+                // TotalU includes spacing between items (not before first or after last)
+                double spacingTotal = UICollection.Count > 1 ? (UICollection.Count - 1) * ItemSpacing : 0;
+                return LineDesireUVSize.U + spacingTotal;
+            }
+        }
 
         public double LineV => LineDesireUVSize.V;
 

tests/HeadlessTest.Ursa/Controls/ElasticWrapPanelTests/Tests.cs

@@ -69,4 +69,151 @@ public class Tests
         window.Show();
         Assert.Equal(2, panel.LineCount);
     }
+
+    [AvaloniaFact]
+    public void ItemSpacing_Applied_Correctly()
+    {
+        var window = new Window() { };
+        var panel = new ElasticWrapPanel
+        {
+            Width = 400,
+            Height = 200,
+            Orientation = Orientation.Horizontal,
+            ItemSpacing = 10,
+        };
+        
+        // Add 3 rectangles of 100x100 with 10px spacing
+        // Total width should be: 100 + 10 + 100 + 10 + 100 = 320
+        for (int i = 0; i < 3; i++)
+        {
+            var rect = new Rectangle
+            {
+                Width = 100,
+                Height = 100,
+            };
+            panel.Children.Add(rect);
+        }
+        
+        window.Content = panel;
+        window.Show();
+        
+        // All 3 should fit on one line
+        Assert.Equal(1, panel.LineCount);
+        
+        // Check that the desired size accounts for spacing
+        Assert.True(panel.DesiredSize.Width >= 320);
+    }
+
+    [AvaloniaFact]
+    public void LineSpacing_Applied_Correctly()
+    {
+        var window = new Window() { };
+        var panel = new ElasticWrapPanel
+        {
+            Width = 200,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+            LineSpacing = 20,
+        };
+        
+        // Add 4 rectangles of 100x100, should wrap to 2 lines
+        for (int i = 0; i < 4; i++)
+        {
+            var rect = new Rectangle
+            {
+                Width = 100,
+                Height = 100,
+            };
+            panel.Children.Add(rect);
+        }
+        
+        window.Content = panel;
+        window.Show();
+        
+        // Should have 2 lines
+        Assert.Equal(2, panel.LineCount);
+        
+        // Total height should be: 100 + 20 + 100 = 220
+        Assert.True(panel.DesiredSize.Height >= 220);
+    }
+
+    [AvaloniaFact]
+    public void ItemSpacing_And_LineSpacing_Together()
+    {
+        var window = new Window() { };
+        var panel = new ElasticWrapPanel
+        {
+            Width = 250,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+            ItemSpacing = 10,
+            LineSpacing = 20,
+        };
+        
+        // Add 4 rectangles of 100x100
+        // With ItemSpacing=10, two items per line need 100 + 10 + 100 = 210 width
+        // With LineSpacing=20, two lines need 100 + 20 + 100 = 220 height
+        for (int i = 0; i < 4; i++)
+        {
+            var rect = new Rectangle
+            {
+                Width = 100,
+                Height = 100,
+            };
+            panel.Children.Add(rect);
+        }
+        
+        window.Content = panel;
+        window.Show();
+        
+        // Should have 2 lines
+        Assert.Equal(2, panel.LineCount);
+        
+        // Check dimensions include spacing
+        Assert.True(panel.DesiredSize.Width >= 210);
+        Assert.True(panel.DesiredSize.Height >= 220);
+    }
+
+    [AvaloniaFact]
+    public void ItemSpacing_Does_Not_Affect_LineCount()
+    {
+        var window = new Window() { };
+        
+        // Panel without spacing - should fit 2 items per line (200 width / 100 per item = 2)
+        var panel1 = new ElasticWrapPanel
+        {
+            Width = 200,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+            ItemSpacing = 0,
+        };
+        
+        for (int i = 0; i < 4; i++)
+        {
+            panel1.Children.Add(new Rectangle { Width = 100, Height = 100 });
+        }
+        
+        // Panel with spacing - items with spacing should fit fewer per line
+        // 100 + 10 + 100 = 210 > 200, so only 1 item per line
+        var panel2 = new ElasticWrapPanel
+        {
+            Width = 200,
+            Height = 400,
+            Orientation = Orientation.Horizontal,
+            ItemSpacing = 10,
+        };
+        
+        for (int i = 0; i < 4; i++)
+        {
+            panel2.Children.Add(new Rectangle { Width = 100, Height = 100 });
+        }
+        
+        window.Content = panel1;
+        window.Show();
+        Assert.Equal(2, panel1.LineCount); // 2 items per line, 4 items total = 2 lines
+        
+        window.Content = panel2;
+        window.UpdateLayout();
+        Assert.Equal(4, panel2.LineCount); // 1 item per line, 4 items total = 4 lines
+    }
 }