Color inversion in XAML

Question

In my WP8 application I want to make a color inversion effect. I have no idea what tools I should use so I'll just explain what I want in a very general terms.

How it is supposed to work: say I have a UserControl that consists of black rectangle and some white text on top of it. I want to apply something to that user control that will invert colors of a part of UserControl that it covers. Some invisible rectangle that spans say 50% of UserControl and in that area background will be white and text will be black. I want it to be dynamic so I can change the area it covers at runtime.

Here's an image to illustrate this:

Inversion effect applied to a half of control.

I believe it's possible to achieve this by using two controls with same text, inverted colors and opacity mask but I wonder if this can be done in a more clean and direct way?

Answer 1

I think what you're looking for ideally would either be two TextBlocks with OpacityMask applied to the one on top like;

<Grid MaxWidth="100">
    <TextBlock Text="Hey check it out we can change object gradients! yay!" Foreground="Red"
               TextWrapping="Wrap" HorizontalAlignment="Center" VerticalAlignment="Center"/>
    <TextBlock Text="Hey check it out we can change object gradients! yay!" Foreground="Blue"
               TextWrapping="Wrap" HorizontalAlignment="Center" VerticalAlignment="Center">
             <TextBlock.OpacityMask>
                 <LinearGradientBrush StartPoint="0.1,0.1" EndPoint="0.75,0.75">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.322" Color="Black"/>
                    <GradientStop Offset="0.739" Color="Transparent"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </TextBlock.OpacityMask>
    </TextBlock>               
</Grid>

Or you could just apply a LinearGradientBrush directly to the Foreground (or Background of other element) itself like;

<Border Width="100" Height="50">
        <Border.Background>
                <LinearGradientBrush StartPoint="0.062,0.552" EndPoint="0.835,0.548">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.5" Color="White"/>
                    <GradientStop Offset="0.5" Color="Black"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Border.Background>

        <TextBlock Text="Hello World!" HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBlock.Foreground>
                <LinearGradientBrush StartPoint="0.1,0.1" EndPoint="0.75,0.75">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.5" Color="Black"/>
                    <GradientStop Offset="0.5" Color="White"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </TextBlock.Foreground>
        </TextBlock>

    </Border>

or gettin 80's style fancy;

<Border Width="100" Height="50">
        <Border.Background>
                <LinearGradientBrush StartPoint="0.472,0.047" EndPoint="0.47,0.942">
                  <LinearGradientBrush.GradientStops>
                    <GradientStop Offset="0.541" Color="White"/>
                    <GradientStop Offset="0.548" Color="Black"/>
                  </LinearGradientBrush.GradientStops>
                </LinearGradientBrush>
            </Border.Background>

            <TextBlock Text="Hello World!" HorizontalAlignment="Center" VerticalAlignment="Center">
                <TextBlock.Foreground>
                    <LinearGradientBrush StartPoint="0.472,0.047" EndPoint="0.47,0.942">
                      <LinearGradientBrush.GradientStops>
                        <GradientStop Offset="0.631" Color="Black"/>
                        <GradientStop Offset="0.635" Color="White"/>
                      </LinearGradientBrush.GradientStops>
                    </LinearGradientBrush>
                </TextBlock.Foreground>
            </TextBlock>

    </Border>

Give that a shot, hope this helps.