Tabs are not properly aligned in TextBox

[mgarstenauer]

Describe the bug

@ajkfds discovered that tabs (\t used for indentation) don't properly line up in AvaloniaEdit. See AvaloniaUI/AvaloniaEdit#412.

This seems to be a text formatting bug in Avalonia. It can be reproduced using a simple TextBox.

To Reproduce

Create a new Avalonia window with the following content:

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        mc:Ignorable="d"
        x:Class="AvaloniaApplication1.MainWindow"
        Title="AvaloniaApplication1" Height="200" Width="300">
    <Grid>
        <TextBox Text="&#x09;a&#x09;a&#x0D;a&#x09;a&#x09;a"/>
    </Grid>
</Window>

Note: The TextBox content is "\ta\ta\na\ta\ta"

This creates the following output in Avalonia:

The 'a' don't line up correctly.

Expected behavior

The 'a' are expected to be aligned. Here is the same window in WPF:

Avalonia version

11.0.6

OS

Windows

Additional context

No response

[Gillibald]

Avalonia only supports fixed-width tabs and does no column layout calculation. There is no bug. This is just a feature that isn't available yet.

[workgroupengineering]

Hi @Gillibald, I would like to work on this feature because I needed it, but I need help designing it.

Initially I was considering adding a FixedTabWidth attached property to TextElement, but I would like to leave the door open for advanced tabs manager like Microsoft Word and Libreoffice Write do. Any suggestions?