Develop Reference

Avalonia UI Pop-Up Overlay

My question is pretty straight forward:
How do I achieve an Overlay Pop-Up effect using avalonia?
What I mean by this is I want to darken the whole Panel that contains my UI elements a little bit (tried the opacity attribute, but it didn't look good and the OpacityMask only seems to support "Transparent" as a color, but I want semi-transparency or even blur if that's possible). Then I want to display a little popup box. If this were CSS I'd be able to do a position: absolute;, however I couldn't figure out how to do this using avalonia.
To visualize what I mean here are some screenshots of a Windows Forms Application where I was able to achieve the desired effect:
My UI without overlay effect:
My UI with overlay effect:
As you can see the whole UI has been darkened a bit while the background is still visible (when using the avalonia Opacity property the effect is not the same and quite inconsistent, as the more panels are on top of each other on a given position the less the background seems to be affected by the Opacity and it just doesn't look good. I can add screenshots of how bad it would look later if you want.)
To sum it up:
1. How do I slightly and consistently darken (or even blur?) a panel with all of its contents, so that stacked panels with the same background color don't become visible, just because the transparency is acting weird?
2. What is the avalonia equivalent to the CSS position: absolute; so I can put my Pop-Up in the middle of the screen and on top of everything else?

You can use the same technique as in WPF:
<Window>
<Grid>
<DockPanel x:Name="YourMainContentGoesHere"/>
<Border IsVisible="{Binding IsPopupVisible}" Background="#40000000">
<YourPopupControlHere Width="200" Height="200"/>
</Border>
</Grid>
</Window>
Unconfigured Grid will display elements on top of each other, semi-transparent Border's background will darken the rest of the content.

Why is the image only partially visible inside my Button?

I am developing a Windows Store app and I've done this before, months ago, but all of a sudden, in this new app, I can't get the image to display inside the button (properly).
<Button x:Name="ShowView" Grid.Column="1" Width="32" Height="32" HorizontalAlignment="Right" VerticalAlignment="Center" Margin="0,61,20,33">
<StackPanel HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
<Image x:Name="ShowViewImage" Source="/Assets/ShowView.png" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" />
</StackPanel>
</Button>
As you can see, the code is fine (unless things have changed drastically, which by the looks of it they haven't). So what gives? This is the only code I have so far in my XAML file other than the defauls that VS generates as it's a new Project.
P.S. I've also tried taking out the StackPanel and just having Button > Image, but this produces the same result.
So, when the BUtton displays at runtime, all I can see is a very tiny, 2pixels of the image (but the image is actually 32x32pixels. How do I properly display an "Image Button"?

The problem is that your Width and Height for the button are far too small. You've made it 32x32 pixels, but the button will use almost all of that itself for the space it leaves around the visible border, the border itself, and the padding between the border and the button's content.
(It leaves space around the edge to provide a larger hit target than the visible appearance. This is useful on touchscreens, where accurate finger placement is difficult.)
All that's left for your image is a few pixels.
You'll need to make the button about 62x52 pixels to leave enough space in the middle for a 32x32 pixel bitmap.
You could get away with a slightly smaller button if you explicitly set smaller Margin and Padding properties, although as mentioned above, the margin is there for a reason.

You have a couple options, the Padding property for instance is Template bound with some pre-set padding added to it. So with your Button having a fixed Height and Width set to 32 something as simple as setting Padding="0" could fix it for you depending on the actual size of your Image.
If worse comes to worse though, you could always just make your own Button Template. There's a couple easy ways to do this. One of which would be just go make a copy of the default Button Template, rip out all the Padding/Margin/Height/Width crap preset in there and just change its name then apply your new template directly to your button like;
<Button x:Name="ShowView" Grid.Column="1" HorizontalAlignment="Right" VerticalAlignment="Center" Margin="0,61,20,33"
Style="{StaticResource YourCustomButtonTemplateForImages}">
<Image x:Name="ShowViewImage" Source="/Assets/ShowView.png"/>
</Button>
Or... another option would be, embed your Image inside of a ViewBox inside your button and it will fit and re-scale itself accordingly to its set available size.
Oh, you might also want to make your Background="Transparent" while you're at it to make it look a little cleaner as just an image.
Hope this helps.

Adding controls over an image in silverlight

There is a Canvas in our application where an image is loaded. We need to provide buttons such as "Add Placemark" on top right corner of the image such that the button highlights on focus.
There are PNG files for these controls. How can I make these PNG behave as buttons (change visual state on hover, onclick etc). I tried to add <Image> in <Button>, but it shows the opaque button on top of the Canvas.
<Button Height="23" HorizontalAlignment="Right" Name="btnAddPlacemark" Margin="3" VerticalAlignment="Top" Width="23" Click="btnAddPlacemark_Click">
<Image Source="/Map_SL;component/Images/PlaceMark.png" Stretch="Fill" />
</Button>

Sounds like you are going to recreate all the logic of a button, simply to remove the border/background. Remember every control in Silverlight is simply skinned and therefore infinitely configurable.
You do want to use a normal button with an image, then restyle the button to remove the parts you don't want. I realise this seems daunting at first, but there are simplified basic skins available to simplify that task, or you can use Expression Blend (if you have access to it or can afford it).
Try this link from the master himself:
http://weblogs.asp.net/scottgu/pages/silverlight-tutorial-part-7-using-control-templates-to-customize-a-control-s-look-and-feel.aspx

Fading in and out a path in silverlight?

I have a path defined as such:
<Viewbox Visibility="Collapsed" x:Name="Tick" Grid.Column="1" Grid.Row="1">
<Canvas MaxWidth="100" MaxHeight="100" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Width="100" Height="100" Canvas.Left="0" Canvas.Top="0">
<Path ...Fill="#FF00B800" x:Name="MyPath" (path dimensions, lines, etc) .../>
</Canvas>
</Viewbox>
Now what I'd like to do is manipulate fill such that it will cause the path to have a fade in/fade out effect. Basically make fills alpha component either move towards opaque or transparent based on whether or not the viewbox the path is inside is Visible. So when visible the path fades in, when collapsed the path fades out.

The effect you are trying achieve is a classy one but there is a serious problem with your current plan. When the Visibility of a higher-level element, Viewbox in this case, is set to Visibility.Collapsed, the element and all sub-elements are immediately no longer visisble. It is at this point that you want the fade-out of the Path to begin.
So the Path is already not visible and starting an animation to gradually reduce its opacity will no do any good because it is already gone. In other words, by the time the visibility is set to Visiblity.Collapsed, it is too late to do anything useful with things inside the element because the user won't see them. If you could, you would want to see into the future and know that you are going to change the visibility and start an animation so that it finishes before you "close the curtain" on the element.
The same problem doesn't apply to when we make the element visible because everything is perfect: we become visible and start the fade-in animation. But since half of the effect is not going to work, we still have a big problem.
The solution to this problem is move up a level and see what we're trying to do. In the XAML we only have passive elements, Viewbox, Canvas, and Path. But maybe these are acting more like controls or assisting controls, for example being the check for a CheckBox or a checkbox-like control.
A control can have states:
Normal, MouseOver
Pressed, Disabled
Unfocused, Focused
and those states can have transition effects, thanks to the VisualStateManager.
So if the fade-in and fade-out effects are part of control behavior, then we have a whole sophisticated powerful toolset available to solve our problem. I don't know if this is the case in your situation.
Even if it is not the case, a very workable approach to transition effects on Silverlight is to transform your elements into a lookless control, solely for the purpose of utilizing the VisualStateManager, because it makes things so easy. Perhaps this alternative can work in your situation.

Surface ScatterViewItem background not transparent

I'm working on a Microsoft Surface and attaching a round image object to a ScatterViewItem. I'm having an issue hiding the background of the square ScatterViewItem. If I go in and set the background to transparent, it's not transparent, it's more like gray translucent. So what I end up with is a round image in the middle sitting on a square with gray translucent edges. How do I hide this? I'm doing this programmatically through C#.

What you're seeing isn't really the svi background, but the shadow that is part of the default template. If you want to get rid of the shadow, you need to redefine the control template.
So like this:
<s:ScatterView>
<s:ScatterViewItem Background="Transparent">
<s:ScatterViewItem.Template>
<ControlTemplate>
<TextBlock>Hello World</TextBlock>
</ControlTemplate>
</s:ScatterViewItem.Template>
</s:ScatterViewItem>
</s:ScatterView>
Be aware that if you replace it like that, you lose all the other little visual flare like the 'pick up' effect and the shimmer. If you want to keep those, just use blend to edit a copy of the existing template and remove the shadow.