Refactor GroupBox elevation (#3217)

* Apply fixed MaxWidth in demo app page

* Adding GroupBox cases to demo app page

* Fix elevation on GroupBox variants

* Update MaterialDesignThemes.Wpf/Converters/IsTransparentBrushConverter.cs
Co-authored-by: NKevin B <Keboo@users.noreply.github.com>

* Return true for null value in IsTransparentBrushConverter

---------
Co-authored-by: NKevin B <Keboo@users.noreply.github.com>

MainDemo.Wpf/GroupBoxes.xaml

-<UserControl x:Class="MaterialDesignDemo.GroupBoxes"
+<UserControl x:Class="MaterialDesignDemo.GroupBoxes"
              xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
              xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
@@ -14,6 +14,10 @@
       <ResourceDictionary.MergedDictionaries>
         <ResourceDictionary Source="pack://application:,,,/MaterialDesignThemes.Wpf;component/Themes/MaterialDesignTheme.GroupBox.xaml" />
       </ResourceDictionary.MergedDictionaries>
+
+      <Style TargetType="smtx:XamlDisplay" BasedOn="{StaticResource {x:Type smtx:XamlDisplay}}">
+        <Setter Property="MaxWidth" Value="350" />
+      </Style>
     </ResourceDictionary>
   </UserControl.Resources>
 
@@ -28,6 +32,7 @@
       <RowDefinition />
       <RowDefinition />
       <RowDefinition />
+      <RowDefinition />
     </Grid.RowDefinitions>
     <smtx:XamlDisplay Grid.Row="0"
                       Grid.Column="0"
@@ -174,6 +179,46 @@
                Source="Resources/Contact.png" />
       </GroupBox>
     </smtx:XamlDisplay>
+
+    <smtx:XamlDisplay Grid.Row="3"
+                      Grid.Column="0"
+                      UniqueKey="groupbox_9">
+      <GroupBox Margin="16"
+                Header="Elevation"
+                Background="White"
+                materialDesign:ElevationAssist.Elevation="Dp6"
+                Style="{StaticResource MaterialDesignGroupBox}">
+        <Grid Height="50">
+          <TextBlock Text="GroupBox (with border) and elevation" VerticalAlignment="Center" />
+        </Grid>
+      </GroupBox>
+    </smtx:XamlDisplay>
+    <smtx:XamlDisplay Grid.Row="3"
+                      Grid.Column="1"
+                      UniqueKey="groupbox_10">
+      <GroupBox Margin="16"
+                Header="Elevation (no border)"
+                Background="White"
+                materialDesign:ElevationAssist.Elevation="Dp6"
+                BorderThickness="0"
+                Style="{StaticResource MaterialDesignGroupBox}">
+        <Grid Height="50">
+          <TextBlock Text="GroupBox (without border) and elevation" VerticalAlignment="Center" />
+        </Grid>
+      </GroupBox>
+    </smtx:XamlDisplay>
+    <smtx:XamlDisplay Grid.Row="3"
+                      Grid.Column="2"
+                      UniqueKey="groupbox_11">
+      <GroupBox Margin="16"
+                Header="Elevation on Card"
+                materialDesign:ElevationAssist.Elevation="Dp6"
+                Style="{StaticResource MaterialDesignCardGroupBox}">
+        <Grid Height="50">
+          <TextBlock Text="GroupBox (using Card style) and elevation" VerticalAlignment="Center" />
+        </Grid>
+      </GroupBox>
+    </smtx:XamlDisplay>
   </Grid>
 </UserControl>
 

MaterialDesignThemes.Wpf/Converters/IsTransparentBrushConverter.cs

+using System.Globalization;
+using System.Windows.Data;
+using System.Windows.Media;
+
+namespace MaterialDesignThemes.Wpf.Converters;
+
+public sealed class IsTransparentBrushConverter : IValueConverter
+{
+    public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+        => value is null || Equals(value, Brushes.Transparent);
+
+    public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+        => throw new NotImplementedException();
+}

MaterialDesignThemes.Wpf/Themes/MaterialDesignTheme.GroupBox.xaml

-<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:converters="clr-namespace:MaterialDesignThemes.Wpf.Converters"
                     xmlns:wpf="clr-namespace:MaterialDesignThemes.Wpf">
 
+  <converters:IsTransparentBrushConverter x:Key="IsTransparentBrushConverter" />
+
   <Style x:Key="MaterialDesignHeaderedContentControl" TargetType="{x:Type HeaderedContentControl}">
     <Setter Property="Template">
       <Setter.Value>
@@ -28,18 +30,17 @@
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate TargetType="{x:Type GroupBox}">
-          <Grid>
-            <Border Background="{TemplateBinding Background}"
+          <Grid x:Name="OuterGrid">
+            <Border x:Name="Border"
+                    Background="{TemplateBinding Background}"
                     BorderBrush="{Binding Path=Background, ElementName=PART_ColorZone}"
                     BorderThickness="{TemplateBinding BorderThickness}" />
-            <DockPanel Background="{TemplateBinding Background}">
+            <DockPanel Margin="{TemplateBinding BorderThickness}">
               <wpf:ColorZone x:Name="PART_ColorZone"
                              Padding="{TemplateBinding Padding}"
                              wpf:ColorZoneAssist.Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Background)}"
                              wpf:ColorZoneAssist.Foreground="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Foreground)}"
-                             wpf:ShadowAssist.ShadowEdges="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ShadowAssist.ShadowEdges)}"
                              DockPanel.Dock="Top"
-                             Effect="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ElevationAssist.Elevation), Converter={x:Static converters:ShadowConverter.Instance}}"
                              Mode="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Mode)}"
                              SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
                              UseLayoutRounding="True">
@@ -57,6 +58,14 @@
                                 SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
             </DockPanel>
           </Grid>
+          <ControlTemplate.Triggers>
+            <DataTrigger Binding="{Binding ElementName=Border, Path=Background, Converter={StaticResource IsTransparentBrushConverter}}" Value="True">
+              <Setter TargetName="PART_ColorZone" Property="Effect" Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ElevationAssist.Elevation), Converter={x:Static converters:ShadowConverter.Instance}}" />
+            </DataTrigger>
+            <DataTrigger Binding="{Binding ElementName=Border, Path=Background, Converter={StaticResource IsTransparentBrushConverter}}" Value="False">
+              <Setter TargetName="OuterGrid" Property="Effect" Value="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ElevationAssist.Elevation), Converter={x:Static converters:ShadowConverter.Instance}}" />
+            </DataTrigger>
+          </ControlTemplate.Triggers>
         </ControlTemplate>
       </Setter.Value>
     </Setter>
@@ -73,14 +82,14 @@
     <Setter Property="Template">
       <Setter.Value>
         <ControlTemplate TargetType="{x:Type GroupBox}">
-          <wpf:Card VerticalAlignment="Stretch">
+          <wpf:Card VerticalAlignment="Stretch"
+                    wpf:ElevationAssist.Elevation="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ElevationAssist.Elevation)}">
             <DockPanel Background="{TemplateBinding Background}">
               <wpf:ColorZone x:Name="PART_ColorZone"
                              Padding="{TemplateBinding Padding}"
                              wpf:ColorZoneAssist.Background="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Background)}"
                              wpf:ColorZoneAssist.Foreground="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Foreground)}"
                              DockPanel.Dock="Top"
-                             Effect="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ElevationAssist.Elevation), Converter={x:Static converters:ShadowConverter.Instance}}"
                              Mode="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=(wpf:ColorZoneAssist.Mode)}">
                 <ContentPresenter ContentSource="Header"
                                   ContentStringFormat="{TemplateBinding HeaderStringFormat}"
@@ -100,6 +109,6 @@
       </Setter.Value>
     </Setter>
     <Setter Property="wpf:ColorZoneAssist.Mode" Value="PrimaryMid" />
-    <Setter Property="wpf:ElevationAssist.Elevation" Value="Dp0" />
+    <Setter Property="wpf:ElevationAssist.Elevation" Value="Dp1" />
   </Style>
-</ResourceDictionary>
\ No newline at end of file
+</ResourceDictionary>