I need apply a ScaleTransform to some textblocks (flip the text, ScaleY = -1) depending on where the textblock is located in the canvas.

My first action was to use the Canvas.GetLeft()/GetTop() but learned that, unless I had positioned the objects with SetLeft()/SetTop(), those functions will return NaN. This is not my scenario because I am applying a stack of transforms using TransformGroup, then learned that I should use TransformToVisual which will provide the measurement I was looking for.

Then I now have 2 problems:

• The measurement will only be provided after everything is already on screen, but I need the transform already applied before ths screen shows, and have no idea which event I should manually trigger, otherwise the offsets will be 0 even with the transform already applied;
• The offsets are provided as relative values, as per the sample codes over MSDN and S.O., but I’d rather have the absolute positions in the canvas.

See the XAML and C# of a sample program that shows this behavior. The TranslateTransform is applied in the constructor and then I immediately show the offsets, which are 0. Then the button does the same thing but with the screen already up, so the relative offsets are displayed.

XAML

<Window x:Class="Canvas_AbsPosition.MainWindow"
        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"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Canvas_AbsPosition"
        mc:Ignorable="d"
        Title="MainWindow" Height="600" Width="500">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="500"></RowDefinition>
            <RowDefinition Height="5"></RowDefinition>
            <RowDefinition Height="25"></RowDefinition>
            <RowDefinition Height="25"></RowDefinition>
        </Grid.RowDefinitions>

        <Canvas Grid.Row="0" x:Name="cv"></Canvas>
        <Separator Grid.Row="1"></Separator>
        <Button Grid.Row="2" x:Name="bt_translate" Content="Move text to center of canvas" Width="200" Click="bt_translate_Click"></Button>
        <Button Grid.Row="3" x:Name="bt_getpos" Content="Get text position in the canvas" Width="200" Click="bt_getpos_Click"></Button>
    </Grid>
</Window>

C#

namespace Canvas_AbsPosition
{
    public partial class MainWindow : Window
    {
        TextBlock text = new TextBlock();

        public MainWindow()
        {
            InitializeComponent();

            text.Text = "Our TextBlock To Be Moved";
            text.FontSize = 20;
            text.FontWeight = FontWeights.Bold;
            text.Measure(new Size());
            text.Arrange(new Rect());       // text.ActualWidth and text.ActualHeight are now available

            cv.Width = cv.Height = 500;
            cv.Children.Add(text);

            cv.Measure(new Size(cv.Width, cv.Height));
            cv.Arrange(new Rect(0, 0, cv.DesiredSize.Width, cv.DesiredSize.Height));    // Forces the computation of cv.ActualWidth and cv.ActualHeight

            // Positions the text in the center of canvas before the window is shown
            text.RenderTransform = new TranslateTransform() { X = (cv.ActualWidth - text.ActualWidth) / 2, Y = (cv.ActualHeight - text.ActualHeight) / 2 };
            var offset = cv.TransformToVisual(text).Transform(new Point());
            MessageBox.Show("X offset: " + offset.X.ToString() + ", Y offset: " + offset.Y.ToString());     // The offsets will be 0 even though the text is already moved
        }

        private void bt_translate_Click(object sender, RoutedEventArgs e)
        {
            text.RenderTransform = new TranslateTransform() { X = (cv.ActualWidth - text.ActualWidth) / 2, Y = (cv.ActualHeight - text.ActualHeight) / 2 };
        }

        private void bt_getpos_Click(object sender, RoutedEventArgs e)
        {
            var offset = cv.TransformToVisual(text).Transform(new Point());
            MessageBox.Show("X offset: " + offset.X.ToString() + ", Y offset: " + offset.Y.ToString());     // After the window is shown, the offsets are available (relative, not absolute)
        }
    }
}

How can I address those 2 problems?