TextBlock.LineHeight behaves unexpectedly

[MartyIX]

Describe the bug

TextBlock.LineHeight does not vertically center text with respect to the available line height.

Steps to reproduce the bug

Use the following snippet demonstrates to demonstrate the unexpected TextBlock.LineHeight behavior:

<Border Background="DimGray">
    <TextBlock LineHeight="50" Text="BEHAVIOR DIFFERENCE" />
</Border>

The snippet gets rendered in the following way:

but I would expect the result to be more like this:

note: I created a repository for it here: https://github.com/MartyIX/LineHeight202404/ (The important part is here: https://github.com/MartyIX/LineHeight202404/blob/main/MainWindow.xaml)

Now my expectation was that BEHAVIOR DIFFERENCE text would be vertically aligned to the center of the gray box. So my expectation was that the behavior would be the same as how HTML & CSS works: https://playcode.io/1828826 where similar code gets rendered as:

(HTML is <div class="label3">BEHAVIOR DIFFERENCE</div> and the corresponding CSS is .label3 { color: brown; background-color: lightgray; line-height: 40px; })

Expected behavior

I would expect the text in TextBlock to be vertically aligned to the center of the line where the text is located.

In the end, I'm not sure if it is a bug or if it works as intended.

Screenshots

No response

NuGet package version

None

Windows version

No response

Additional context

Tested using: <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.4.230913002" /> (see https://github.com/MartyIX/LineHeight202404/blob/c6a2ed2b0a0c6acdeebcfa09550b7bb5e5270b79/LineHeight202404.csproj#L26)

I have filed the dotnet/maui#21705 issue but then I decided to try in a vanilla WinUI app to understand who is responsible for the behavior.

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[MartyIX]

@codendone Do i understand right that this is a bug?

[codendone]

@MartyIX I expect this is by design, at least for the current design. The WPF documentation has more information about LineHeight behavior, including this important line:

In addition to this property, the layout of lines in a TextBlock is affected by its LineStackingStrategy property.

The LineStackingStrategy does have an impact here. I don't know if there are additional properties currently to manage this or if this would be a feature request.

[MartyIX]

I tried various variants:

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="LineHeight202404.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:LineHeight202404"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <ScrollView>
        <StackPanel Orientation="Vertical" HorizontalAlignment="Center" VerticalAlignment="Center">

            <Border Background="DimGray" Height="Auto">
                <TextBlock Text="Test text #1: TextLineBounds=Tight" LineHeight="50" TextLineBounds="Tight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="LightBlue" Height="Auto">
                <TextBlock Text="Test text #2: TextLineBounds=Full" LineHeight="50" TextLineBounds="Full" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="DimGray" Height="Auto">
                <TextBlock Text="Test text #3: TextLineBounds=TrimToBaseline" LineHeight="50" TextLineBounds="TrimToBaseline" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="LightBlue" Height="Auto">
                <TextBlock Text="Test text #4: TextLineBounds=TrimToCapHeight" LineHeight="50" TextLineBounds="TrimToCapHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="DimGray" Height="Auto">
                <TextBlock Text="Test text #5: LineStackingStrategy=BaselineToBaseline" LineHeight="50" LineStackingStrategy="BaselineToBaseline" SelectionHighlightColor="AliceBlue"
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="Firebrick" Height="Auto">
                <TextBlock Text="Test text #5b: LineStackingStrategy=BaselineToBaseline, Padding=0,5" Padding="0,5" LineHeight="50" LineStackingStrategy="BaselineToBaseline" 
                           SelectionHighlightColor="AliceBlue" IsTextSelectionEnabled="True" Foreground="Black" />
            </Border>

            <Border Background="Aquamarine" Height="Auto">
                <TextBlock Padding="0,5" LineHeight="50" LineStackingStrategy="BaselineToBaseline" 
                           SelectionHighlightColor="AliceBlue" IsTextSelectionEnabled="True" Foreground="Black">
                    Test text #5c: LineStackingStrategy=BaselineToBaseline, Padding=0,5, multiline
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightBlue" Height="Auto">
                <TextBlock Text="Test text #6: LineStackingStrategy=BlockLineHeight" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="LightPink" Height="Auto">
                <TextBlock Text="Test text #7: LineStackingStrategy=MaxHeight" LineHeight="50" LineStackingStrategy="MaxHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" />
            </Border>

            <Border Background="LightGray" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="MaxHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #8: TextWrapping=Wrap
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightBlue" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="MaxHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #9: TextWrapping=Wrap, LineStackingStrategy=MaxHeight 
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightGray" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="MaxHeight" TextLineBounds="Tight" 
                           SelectionHighlightColor="AliceBlue"  IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #9b: TextWrapping=Wrap, LineStackingStrategy=MaxHeight, TextLineBounds=Tight
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightSkyBlue" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="MaxHeight" TextLineBounds="Full" 
                           SelectionHighlightColor="AliceBlue"  IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #9c: TextWrapping=Wrap, LineStackingStrategy=MaxHeight, TextLineBounds=Full
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightSteelBlue" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="MaxHeight" TextLineBounds="TrimToCapHeight" 
                           SelectionHighlightColor="AliceBlue"  IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #9d: TextWrapping=Wrap, LineStackingStrategy=MaxHeight, TextLineBounds=TrimToCapHeight
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightCoral" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #10: TextWrapping=Wrap, LineStackingStrategy=BlockLineHeight 
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightGoldenrodYellow" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" TextLineBounds="Full" >
                    Test text #10b: TextWrapping=Wrap, LineStackingStrategy=BlockLineHeight, TextLineBounds=Full 
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightGray" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" TextLineBounds="Tight" >
                    Test text #10c: TextWrapping=Wrap, LineStackingStrategy=BlockLineHeight, TextLineBounds=Tight
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightPink" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" TextLineBounds="TrimToBaseline" >
                    Test text #10d: TextWrapping=Wrap, LineStackingStrategy=BlockLineHeight, TextLineBounds=TrimToBaseline
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightSeaGreen" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BlockLineHeight" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black" TextLineBounds="TrimToCapHeight" >
                    Test text #10e: TextWrapping=Wrap, LineStackingStrategy=BlockLineHeight, TextLineBounds=TrimToCapHeight
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightGreen" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BaselineToBaseline" SelectionHighlightColor="AliceBlue" 
                           IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #11: TextWrapping=Wrap, LineStackingStrategy=BaselineToBaseline
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightGray" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BaselineToBaseline" TextLineBounds="Full" 
                           SelectionHighlightColor="AliceBlue"  IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #12: TextWrapping=Wrap, LineStackingStrategy=BaselineToBaseline, TextLineBounds=Full
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>

            <Border Background="LightSalmon" Height="Auto">
                <TextBlock TextWrapping="Wrap" LineHeight="50" LineStackingStrategy="BaselineToBaseline" TextLineBounds="Tight" 
                           SelectionHighlightColor="AliceBlue" IsTextSelectionEnabled="True" Padding="0" Foreground="Black">
                    Test text #13: TextWrapping=Wrap, LineStackingStrategy=BaselineToBaseline, TextLineBounds=Tight
                     <LineBreak/>
                    Second line
                </TextBlock>
            </Border>
        </StackPanel>
    </ScrollView>
</Window>

renders as

Unfortunately, none seems to do what I would like.