Develop Reference

Video brush orientation in Windows Phone Silverlight 8.1

I am trying to set the video brush (viewfinderBrush) for the rectangle(viewfinderRectangle) fill property.
Using the following composite transform, the preview of the video can be viewed but it looks like mirror reflection. (for eg. If I try to move the finger from left to right, it shows right to left). I also added my xaml code, which has only the rectangle.
viewfinderBrush.RelativeTransform =
new CompositeTransform() { CenterX = 0.5, CenterY = 0.5, Rotation = 270, ScaleX = -1 };
viewfinderRectangle.Fill = viewfinderBrush;
Xaml Code
<Rectangle x:Name="viewfinderRectangle" Width="640" Height="480" HorizontalAlignment="Left" />
Please let me know, to overcome this issue.

How to draw a rectangle on a WPF canvas

I'm trying to draw a Rectangle on a Canvas as follows:
System.Windows.Shapes.Rectangle rect;
rect = new System.Windows.Shapes.Rectangle();
rect.Stroke = new SolidColorBrush(Colors.Black);
rect.Fill = new SolidColorBrush(Colors.Black);
rect.Width=200;
rect.Height=200;
Canvas.SetLeft(rect,0);
Canvas.SetTop(rect,0);
front_canvas.Children.Add(rect);
Why would this code not draw a rectangle?
The canvas is defined in the associated XAML as follows:
<Canvas Height="200" Width="200" Name="front_canvas" Grid.Row="1" Grid.Column="0">
</Canvas>
The canvas shows up fine. I can tell because of the gap it leaves in the layout grid.

This should draw your rectangle as a 200x200 black square, provided front_canvas is displayed correctly.
Why would this code not draw a rectangle?
The main reasons this would not draw are:
front_canvas is not visible
front_canvas is not in the visual tree and being displayed correctly
Some other FrameworkElement is obscuring front_canvas, at least the upper left corner.
There is another object in the canvas at a higher z order.
Note that you'd typically also want to set StrokeThickness if you want to see the Stroke you specify.

To View Rectangle you must specify the StrokeThickness and set any Integer value greater than zero:
rect.StrokeThickness=2;

// ...
front_canvas.Children.Add(rect);
Size size = new Size(front_canvas.Width, front_canvas.Height);
front_canvas.Measure(size);
front_canvas.Arrange(new Rect(size));

Find size of a Canvas

How to find out size of an Canvas that created in xaml file?
for example I create an Canvas by
<Page
x:Class="MyApp.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:MyApp"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Canvas x:Name="canvas" Background="White">
</Canvas>
</Page>
and full screen is white or whatever color I specified for that canvas
than in my class I tried but with no luck
double h = canvas.Height; // NaN
h = canvas.ActualHeight; // 0
so how do I found out the actual size of that canvas? or the size is 0 but than how to make the canvas full screen size?
I am new C# and metro developer and so confused how everything works compare to iOS.

Where in your code are you checking the size of the Canvas? I'm assuming you're doing it in the page constructor or somewhere else that is running before the UI layout has run. In this case, all auto sized elements (NaN height or width) still have their default size. If you check the size after layout has completed, like in a Loaded event handler in your page, then you should see the true rendered size.

If your Canvas happens to only contain one Image, you can use:
var Width = ((Image) (MyCanvas.Children[0])).Width;
var Height = ((Image) (MyCanvas.Children[0])).Height;
Of course, you can switch out the two Image casts for another element, if your Canvas contains one of some other item.
Alternatively just give the wrapped Image (or other element) a name, and reference it as MyImage.Width.

WPF databinding problem

I have a grid inside a canvas on a tab.
The grid contains a large bitmap image,
I have(tried to) bound the size of the grid to the size of the tab and also have a five pixel margin around the grid.
imageTab.cs
public ImageTab(SendInfo sendInfo, int numImge, int numAccs)
{
imageDisplay = new ImageDisplay(sendInfo, numImge, numAccs);
imageDisplay.ClipToBounds = true;
CreateCanvas();
}
private void CreateCanvas()
{
Canvas canvas = new Canvas();
canvas.Children.Add(imageDisplay);
this.AddChild(canvas);
}
ImageDisplay.xaml
<UserControl x:Class="MyProj.ImageDisplay">
<Grid Margin="5,5,5,5" Height="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=TabControl, AncestorLevel=1}, Path=ActualHeight}">
<Image/>
</Grid>
</UserControl>
The grid comes off the bottom of the tab area slightly causing the bottom of the image to be cut off.
Is there a problem with my databinding, do I need to apply some sort of offset to it? (size of tab - 10pixels for the margin?)

You don't need to set the Height property at all (also realize that it is incorrect to do so as you have it when you consider the 5 pixel margin, i.e., it would be off by 10 pixels).
Just leave VerticalAlignment and HorizontalAlignment at their default values (which is Stretch) to get the effect you are after here.
Try this on a new Window to see what I mean:
<Window x:Class="WpfApplication9.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="438" Width="587" Background="Pink">
<Grid Background="Black" Margin="5">
</Grid>
</Window>
The grid here will be black and will always stretch to the size of the window, using a 5 pixel margin which you will see because the Window's back color is pink.

WPF element positioning on a Canvas

I have a point on a canvas that I want to place an ellipse. I want the centre of the ellipse to be over this point. At the moment the top left most edge of the ellipse is over this point.
I know I can shift the ellipse programmatically on the canvas but I was wondering if there is a way to tell WPF to centre the element over the point instead of sizing it from the top left???

I do not know of any in built in feature in Ellipse to set its center on a point, but you can extend the Ellipse class to do it.
Add this class to project
public static class EllipseX
{
public static void SetCenter(this Ellipse ellipse, double X, double Y)
{
Canvas.SetTop(ellipse, Y - ellipse.Height/2);
Canvas.SetLeft(ellipse, X - ellipse.Width/2);
}
}
Then in xaml create the Ellipse
<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<Canvas Background="LightGray">
<Ellipse
Name="myEllipse"
Fill="Red"
Height="75"
Width="75"
/>
</Canvas>
</Window>
Then write int following code in code behind:
myEllipse.SetCenter(200,200);
The advantage of this is that you do not have to repeat the logic of finding center in every ellipse you create.
Hope this helps.

No there is no such way. Top Left is a top left, because it's a top left :). Alternatively instead of shifting ellipse you can shift point, if you know ellipse dimensions.

You could apply a TranslateTransform to the Ellipse, but that requires you to know its width and height.

I had a similar problem setting the Center of a ScaleTransform in a style of different sized controls.
Ended up using a converter to bind to the ActualWidth/ActualHeight divided by 2. THe same should work for you with a TranslateTransform as Rune Grimstad mentioned.
<ScaleTransform CenterX="{Binding ActualWidth, Converter={StaticResource divisionConverter}}"
CenterY="{Binding ActualHeight, Converter={StaticResource divisionConverter}}"
ScaleX="1.2"
ScaleY="1.2" />