Layout transform in Windows 8 WinRT XAML

Layout transform is an interesting concept in XAML development. This of course includes WPF, Silverlight, Silverlight for Windows Phone, WinRT XAML. It is often a nice feature (let’s call it a design feature) to have your text rotated 90 degrees to save vertical space. This is especially true on Windows 8 devices where the standard layout includes more horizontal than vertical space. Usually, one would try to use render transform and rotation, but that doesn’t work as expected.

And it shouldn’t really, because there’s a huge difference between rotating using render and layout transform. Not to reinvent the wheel, here is a great blog post that explains it:

http://www.scottlogic.co.uk/blog/colin/2008/12/layouttransform-vs-rendertransform-whats-the-difference/

Please notice that this is the article from 2008, and it still works so well because it’s written for WPF. Here’s the essential difference:

… any transformations associated with an elements LayoutTransform property will have an impact on the subsequent Measure and Arrange steps. Whereas a RenderTransform will not have any impact on the layout process and will only effect rendering…

And it’s best explained with two screenshots.

Render transform

image

Code:

<StackPanel Background="{StaticResource ApplicationPageBackgroundThemeBrush}">  
        <Button Content="First" />
        <Button Content="Second" />
        <Button Content="Third" />
        <Button Content="Fourth">
            <Button.RenderTransform>
                <RotateTransform Angle="-75" />
            </Button.RenderTransform>
        </Button>
        <Button Content="Fifth" />
        <Button Content="Sixth" />
</StackPanel>

I added 6 buttons, and rotated one for –75 degrees. And what I got on the screen was not what I would expect. I would expect my button to rotate but not render over the other elements to look so ugly. I would want my button to have it’s own space. For that I need LayoutTransform.

Layout transform

image

Code:
<Page  
    x:Class="Transforming.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Transforming"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    xmlns:common="using:Transforming.Common"
    mc:Ignorable="d">

    <StackPanel Background="{StaticResource ApplicationPageBackgroundThemeBrush}">
        <Button Content="First" />
        <Button Content="Second" />
        <Button Content="Third" />
        <common:LayoutTransformer HorizontalAlignment="Left">
            <common:LayoutTransformer.LayoutTransform>
                <RotateTransform Angle="-75"/>
            </common:LayoutTransformer.LayoutTransform>
            <Button Content="Fourth" />
        </common:LayoutTransformer>
        <Button Content="Fifth" />
        <Button Content="Sixth" />
    </StackPanel>
</Page>

I added the whole XAML this time to make you notice that I added common in my list of namespaces in order to include the classes from the Common folder, where LayoutTransformer lives. And what is LayoutTransformer? It’s a class published by Microsoft under Microsoft Public License (Ms-PL) as a part of Silverlight Toolkit. Considering that it’s really easy to switch between Silverlight XAML and WinRT XAML, I modified the LayoutTransformer class to work with WinRT and copied the basic defining style to StandardStyles.xaml, which is a resource dictionary that’s part of the standard WinRT project. Here’s the LayoutTransformer class:

Download Layout Transformer class here

// (c) Copyright Microsoft Corporation.  
// This source is subject to the Microsoft Public License (Ms-PL).
// Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
// All other rights reserved.

// Un-comment the following line for diagnostic output
// #define DIAGNOSTICWRITELINE

using System;  
using System.Diagnostics.CodeAnalysis;  
using System.Windows;  
using Windows.Foundation;  
using Windows.UI.Xaml;  
using Windows.UI.Xaml.Controls;  
using Windows.UI.Xaml.Media;

namespace Transforming.Common  
{
    /// <summary>
    /// Represents a control that applies a layout transformation to its Content.
    /// </summary>
    /// <QualityBand>Preview</QualityBand>
    [TemplatePart(Name = TransformRootName, Type = typeof(Grid))]
    [TemplatePart(Name = PresenterName, Type = typeof(ContentPresenter))]
    public sealed class LayoutTransformer : ContentControl
    {
        /// <summary>
        /// Name of the TransformRoot template part.
        /// </summary>
        private const string TransformRootName = "TransformRoot";

        /// <summary>
        /// Name of the Presenter template part.
        /// </summary>
        private const string PresenterName = "Presenter";

        /// <summary>
        /// Gets or sets the layout transform to apply on the LayoutTransformer 
        /// control content.
        /// </summary>
        /// <remarks>
        /// Corresponds to UIElement.LayoutTransform.
        /// </remarks>
        public Transform LayoutTransform
        {
            get { return (Transform)GetValue(LayoutTransformProperty); }
            set { SetValue(LayoutTransformProperty, value); }
        }

        /// <summary>
        /// Identifies the LayoutTransform DependencyProperty.
        /// </summary>
        public static readonly DependencyProperty LayoutTransformProperty = DependencyProperty.Register(
            "LayoutTransform", typeof(Transform), typeof(LayoutTransformer), new PropertyMetadata(null, LayoutTransformChanged));

        /// <summary>
        /// Gets the child element being transformed.
        /// </summary>
        private FrameworkElement Child
        {
            get
            {
                // Preferred child is the content; fall back to the presenter itself
                return (null != _contentPresenter) ?
                    (_contentPresenter.Content as FrameworkElement ?? _contentPresenter) :
                    null;
            }
        }

        // Note: AcceptableDelta and DecimalsAfterRound work around double arithmetic rounding issues on Silverlight.

        /// <summary>
        /// Acceptable difference between two doubles.
        /// </summary>
        private const double AcceptableDelta = 0.0001;

        /// <summary>
        /// Number of decimals to round the Matrix to.
        /// </summary>
        private const int DecimalsAfterRound = 4;

        /// <summary>
        /// Root element for performing transformations.
        /// </summary>
        private Panel _transformRoot;

        /// <summary>
        /// ContentPresenter element for displaying the content.
        /// </summary>
        private ContentPresenter _contentPresenter;

        /// <summary>
        /// RenderTransform/MatrixTransform applied to _transformRoot.
        /// </summary>
        private MatrixTransform _matrixTransform;

        /// <summary>
        /// Transformation matrix corresponding to _matrixTransform.
        /// </summary>
        private Matrix _transformation;

        /// <summary>
        /// Actual DesiredSize of Child element (the value it returned from its MeasureOverride method).
        /// </summary>
        private Size _childActualSize = Size.Empty;

        /// <summary>
        /// Initializes a new instance of the LayoutTransformer class.
        /// </summary>
        public LayoutTransformer()
        {
            // Associated default style
            DefaultStyleKey = typeof(LayoutTransformer);

            // Can't tab to LayoutTransformer
            IsTabStop = false;
#if SILVERLIGHT
            // Disable layout rounding because its rounding of values confuses things
            UseLayoutRounding = false;
#endif
        }

        /// <summary>
        /// Builds the visual tree for the LayoutTransformer control when a new 
        /// template is applied.
        /// </summary>
        protected override void OnApplyTemplate()
        {
            // Apply new template
            base.OnApplyTemplate();
            // Find template parts
            _transformRoot = GetTemplateChild(TransformRootName) as Grid;
            _contentPresenter = GetTemplateChild(PresenterName) as ContentPresenter;
            _matrixTransform = new MatrixTransform();
            if (null != _transformRoot)
            {
                _transformRoot.RenderTransform = _matrixTransform;
            }
            // Apply the current transform
            ApplyLayoutTransform();
        }

        /// <summary>
        /// Handles changes to the Transform DependencyProperty.
        /// </summary>
        /// <param name="o">Source of the change.</param>
        /// <param name="e">Event args.</param>
        private static void LayoutTransformChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            // Casts are safe because Silverlight is enforcing the types
            ((LayoutTransformer)o).ProcessTransform((Transform)e.NewValue);
        }

        /// <summary>
        /// Applies the layout transform on the LayoutTransformer control content.
        /// </summary>
        /// <remarks>
        /// Only used in advanced scenarios (like animating the LayoutTransform). 
        /// Should be used to notify the LayoutTransformer control that some aspect 
        /// of its Transform property has changed. 
        /// </remarks>
        public void ApplyLayoutTransform()
        {
            ProcessTransform(LayoutTransform);
        }

        /// <summary>
        /// Processes the Transform to determine the corresponding Matrix.
        /// </summary>
        /// <param name="transform">Transform to process.</param>
        private void ProcessTransform(Transform transform)
        {
            // Get the transform matrix and apply it
            _transformation = RoundMatrix(GetTransformMatrix(transform), DecimalsAfterRound);
            if (null != _matrixTransform)
            {
                _matrixTransform.Matrix = _transformation;
            }
            // New transform means re-layout is necessary
            InvalidateMeasure();
        }

        /// <summary>
        /// Walks the Transform(Group) and returns the corresponding Matrix.
        /// </summary>
        /// <param name="transform">Transform(Group) to walk.</param>
        /// <returns>Computed Matrix.</returns>
        private Matrix GetTransformMatrix(Transform transform)
        {
            if (null != transform)
            {
                // WPF equivalent of this entire method:
                // return transform.Value;

                // Process the TransformGroup
                TransformGroup transformGroup = transform as TransformGroup;
                if (null != transformGroup)
                {
                    Matrix groupMatrix = Matrix.Identity;
                    foreach (Transform child in transformGroup.Children)
                    {
                        groupMatrix = MatrixMultiply(groupMatrix, GetTransformMatrix(child));
                    }
                    return groupMatrix;
                }

                // Process the RotateTransform
                RotateTransform rotateTransform = transform as RotateTransform;
                if (null != rotateTransform)
                {
                    double angle = rotateTransform.Angle;
                    double angleRadians = (2 * Math.PI * angle) / 360;
                    double sine = Math.Sin(angleRadians);
                    double cosine = Math.Cos(angleRadians);
                    return new Matrix(cosine, sine, -sine, cosine, 0, 0);
                }

                // Process the ScaleTransform
                ScaleTransform scaleTransform = transform as ScaleTransform;
                if (null != scaleTransform)
                {
                    double scaleX = scaleTransform.ScaleX;
                    double scaleY = scaleTransform.ScaleY;
                    return new Matrix(scaleX, 0, 0, scaleY, 0, 0);
                }

                // Process the SkewTransform
                SkewTransform skewTransform = transform as SkewTransform;
                if (null != skewTransform)
                {
                    double angleX = skewTransform.AngleX;
                    double angleY = skewTransform.AngleY;
                    double angleXRadians = (2 * Math.PI * angleX) / 360;
                    double angleYRadians = (2 * Math.PI * angleY) / 360;
                    return new Matrix(1, angleYRadians, angleXRadians, 1, 0, 0);
                }

                // Process the MatrixTransform
                MatrixTransform matrixTransform = transform as MatrixTransform;
                if (null != matrixTransform)
                {
                    return matrixTransform.Matrix;
                }

                // TranslateTransform has no effect in LayoutTransform
            }

            // Fall back to no-op transformation
            return Matrix.Identity;
        }

        /// <summary>
        /// Provides the behavior for the "Measure" pass of layout.
        /// </summary>
        /// <param name="availableSize">The available size that this element can give to child elements.</param>
        /// <returns>The size that this element determines it needs during layout, based on its calculations of child element sizes.</returns>
        protected override Size MeasureOverride(Size availableSize)
        {
            FrameworkElement child = Child;
            if ((null == _transformRoot) || (null == child))
            {
                // No content, no size
                return Size.Empty;
            }

            //DiagnosticWriteLine("MeasureOverride < " + availableSize);
            Size measureSize;
            if (_childActualSize == Size.Empty)
            {
                // Determine the largest size after the transformation
                measureSize = ComputeLargestTransformedSize(availableSize);
            }
            else
            {
                // Previous measure/arrange pass determined that Child.DesiredSize was larger than believed
                //DiagnosticWriteLine("  Using _childActualSize");
                measureSize = _childActualSize;
            }

            // Perform a mesaure on the _transformRoot (containing Child)
            //DiagnosticWriteLine("  _transformRoot.Measure < " + measureSize);
            _transformRoot.Measure(measureSize);
            //DiagnosticWriteLine("  _transformRoot.DesiredSize = " + _transformRoot.DesiredSize);

            // WPF equivalent of _childActualSize technique (much simpler, but doesn't work on Silverlight 2)
            // // If the child is going to render larger than the available size, re-measure according to that size
            // child.Arrange(new Rect());
            // if (child.RenderSize != child.DesiredSize)
            // {
            //     _transformRoot.Measure(child.RenderSize);
            // }

            // Transform DesiredSize to find its width/height
            Rect transformedDesiredRect = RectTransform(new Rect(0, 0, _transformRoot.DesiredSize.Width, _transformRoot.DesiredSize.Height), _transformation);
            Size transformedDesiredSize = new Size(transformedDesiredRect.Width, transformedDesiredRect.Height);

            // Return result to allocate enough space for the transformation
            //DiagnosticWriteLine("MeasureOverride > " + transformedDesiredSize);
            return transformedDesiredSize;
        }

        /// <summary>
        /// Provides the behavior for the "Arrange" pass of layout.
        /// </summary>
        /// <param name="finalSize">The final area within the parent that this element should use to arrange itself and its children.</param>
        /// <returns>The actual size used.</returns>
        /// <remarks>
        /// Using the WPF paramater name finalSize instead of Silverlight's finalSize for clarity
        /// </remarks>
        protected override Size ArrangeOverride(Size finalSize)
        {
            FrameworkElement child = Child;
            if ((null == _transformRoot) || (null == child))
            {
                // No child, use whatever was given
                return finalSize;
            }

            //DiagnosticWriteLine("ArrangeOverride < " + finalSize);
            // Determine the largest available size after the transformation
            Size finalSizeTransformed = ComputeLargestTransformedSize(finalSize);
            if (IsSizeSmaller(finalSizeTransformed, _transformRoot.DesiredSize))
            {
                // Some elements do not like being given less space than they asked for (ex: TextBlock)
                // Bump the working size up to do the right thing by them
                //DiagnosticWriteLine("  Replacing finalSizeTransformed with larger _transformRoot.DesiredSize");
                finalSizeTransformed = _transformRoot.DesiredSize;
            }
            //DiagnosticWriteLine("  finalSizeTransformed = " + finalSizeTransformed);

            // Transform the working size to find its width/height
            Rect transformedRect = RectTransform(new Rect(0, 0, finalSizeTransformed.Width, finalSizeTransformed.Height), _transformation);
            // Create the Arrange rect to center the transformed content
            Rect finalRect = new Rect(
                -transformedRect.Left + ((finalSize.Width - transformedRect.Width) / 2),
                -transformedRect.Top + ((finalSize.Height - transformedRect.Height) / 2),
                finalSizeTransformed.Width,
                finalSizeTransformed.Height);

            // Perform an Arrange on _transformRoot (containing Child)
            //DiagnosticWriteLine("  _transformRoot.Arrange < " + finalRect);
            _transformRoot.Arrange(finalRect);
            //DiagnosticWriteLine("  Child.RenderSize = " + child.RenderSize);

            // This is the first opportunity under Silverlight to find out the Child's true DesiredSize
            if (IsSizeSmaller(finalSizeTransformed, child.RenderSize) && (Size.Empty == _childActualSize))
            {
                // Unfortunately, all the work so far is invalid because the wrong DesiredSize was used
                //DiagnosticWriteLine("  finalSizeTransformed smaller than Child.RenderSize");
                // Make a note of the actual DesiredSize
                _childActualSize = new Size(child.ActualWidth, child.ActualHeight);
                //DiagnosticWriteLine("  _childActualSize = " + _childActualSize);
                // Force a new measure/arrange pass
                InvalidateMeasure();
            }
            else
            {
                // Clear the "need to measure/arrange again" flag
                _childActualSize = Size.Empty;
            }
            //DiagnosticWriteLine("  _transformRoot.RenderSize = " + _transformRoot.RenderSize);

            // Return result to perform the transformation
            //DiagnosticWriteLine("ArrangeOverride > " + finalSize);
            return finalSize;
        }

        /// <summary>
        /// Compute the largest usable size (greatest area) after applying the transformation to the specified bounds.
        /// </summary>
        /// <param name="arrangeBounds">Arrange bounds.</param>
        /// <returns>Largest Size possible.</returns>
        [SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity", Justification = "Closely corresponds to WPF's FrameworkElement.FindMaximalAreaLocalSpaceRect.")]
        private Size ComputeLargestTransformedSize(Size arrangeBounds)
        {
            //DiagnosticWriteLine("  ComputeLargestTransformedSize < " + arrangeBounds);

            // Computed largest transformed size
            Size computedSize = Size.Empty;

            // Detect infinite bounds and constrain the scenario
            bool infiniteWidth = double.IsInfinity(arrangeBounds.Width);
            if (infiniteWidth)
            {
                arrangeBounds.Width = arrangeBounds.Height;
            }
            bool infiniteHeight = double.IsInfinity(arrangeBounds.Height);
            if (infiniteHeight)
            {
                arrangeBounds.Height = arrangeBounds.Width;
            }

            // Capture the matrix parameters
            double a = _transformation.M11;
            double b = _transformation.M12;
            double c = _transformation.M21;
            double d = _transformation.M22;

            // Compute maximum possible transformed width/height based on starting width/height
            // These constraints define two lines in the positive x/y quadrant
            double maxWidthFromWidth = Math.Abs(arrangeBounds.Width / a);
            double maxHeightFromWidth = Math.Abs(arrangeBounds.Width / c);
            double maxWidthFromHeight = Math.Abs(arrangeBounds.Height / b);
            double maxHeightFromHeight = Math.Abs(arrangeBounds.Height / d);

            // The transformed width/height that maximize the area under each segment is its midpoint
            // At most one of the two midpoints will satisfy both constraints
            double idealWidthFromWidth = maxWidthFromWidth / 2;
            double idealHeightFromWidth = maxHeightFromWidth / 2;
            double idealWidthFromHeight = maxWidthFromHeight / 2;
            double idealHeightFromHeight = maxHeightFromHeight / 2;

            // Compute slope of both constraint lines
            double slopeFromWidth = -(maxHeightFromWidth / maxWidthFromWidth);
            double slopeFromHeight = -(maxHeightFromHeight / maxWidthFromHeight);

            if ((0 == arrangeBounds.Width) || (0 == arrangeBounds.Height))
            {
                // Check for empty bounds
                computedSize = new Size(arrangeBounds.Width, arrangeBounds.Height);
            }
            else if (infiniteWidth && infiniteHeight)
            {
                // Check for completely unbound scenario
                computedSize = new Size(double.PositiveInfinity, double.PositiveInfinity);
            }
            else if (!MatrixHasInverse(_transformation))
            {
                // Check for singular matrix
                computedSize = new Size(0, 0);
            }
            else if ((0 == b) || (0 == c))
            {
                // Check for 0/180 degree special cases
                double maxHeight = (infiniteHeight ? double.PositiveInfinity : maxHeightFromHeight);
                double maxWidth = (infiniteWidth ? double.PositiveInfinity : maxWidthFromWidth);
                if ((0 == b) && (0 == c))
                {
                    // No constraints
                    computedSize = new Size(maxWidth, maxHeight);
                }
                else if (0 == b)
                {
                    // Constrained by width
                    double computedHeight = Math.Min(idealHeightFromWidth, maxHeight);
                    computedSize = new Size(
                        maxWidth - Math.Abs((c * computedHeight) / a),
                        computedHeight);
                }
                else if (0 == c)
                {
                    // Constrained by height
                    double computedWidth = Math.Min(idealWidthFromHeight, maxWidth);
                    computedSize = new Size(
                        computedWidth,
                        maxHeight - Math.Abs((b * computedWidth) / d));
                }
            }
            else if ((0 == a) || (0 == d))
            {
                // Check for 90/270 degree special cases
                double maxWidth = (infiniteHeight ? double.PositiveInfinity : maxWidthFromHeight);
                double maxHeight = (infiniteWidth ? double.PositiveInfinity : maxHeightFromWidth);
                if ((0 == a) && (0 == d))
                {
                    // No constraints
                    computedSize = new Size(maxWidth, maxHeight);
                }
                else if (0 == a)
                {
                    // Constrained by width
                    double computedHeight = Math.Min(idealHeightFromHeight, maxHeight);
                    computedSize = new Size(
                        maxWidth - Math.Abs((d * computedHeight) / b),
                        computedHeight);
                }
                else if (0 == d)
                {
                    // Constrained by height
                    double computedWidth = Math.Min(idealWidthFromWidth, maxWidth);
                    computedSize = new Size(
                        computedWidth,
                        maxHeight - Math.Abs((a * computedWidth) / c));
                }
            }
            else if (idealHeightFromWidth <= ((slopeFromHeight * idealWidthFromWidth) + maxHeightFromHeight))
            {
                // Check the width midpoint for viability (by being below the height constraint line)
                computedSize = new Size(idealWidthFromWidth, idealHeightFromWidth);
            }
            else if (idealHeightFromHeight <= ((slopeFromWidth * idealWidthFromHeight) + maxHeightFromWidth))
            {
                // Check the height midpoint for viability (by being below the width constraint line)
                computedSize = new Size(idealWidthFromHeight, idealHeightFromHeight);
            }
            else
            {
                // Neither midpoint is viable; use the intersection of the two constraint lines instead
                // Compute width by setting heights equal (m1*x+c1=m2*x+c2)
                double computedWidth = (maxHeightFromHeight - maxHeightFromWidth) / (slopeFromWidth - slopeFromHeight);
                // Compute height from width constraint line (y=m*x+c; using height would give same result)
                computedSize = new Size(
                    computedWidth,
                    (slopeFromWidth * computedWidth) + maxHeightFromWidth);
            }

            // Return result
            //DiagnosticWriteLine("  ComputeLargestTransformedSize > " + computedSize);
            return computedSize;
        }

        /// <summary>
        /// Returns true if Size a is smaller than Size b in either dimension.
        /// </summary>
        /// <param name="a">Second Size.</param>
        /// <param name="b">First Size.</param>
        /// <returns>True if Size a is smaller than Size b in either dimension.</returns>
        private static bool IsSizeSmaller(Size a, Size b)
        {
            // WPF equivalent of following code:
            // return ((a.Width < b.Width) || (a.Height < b.Height));
            return ((a.Width + AcceptableDelta < b.Width) || (a.Height + AcceptableDelta < b.Height));
        }

        /// <summary>
        /// Rounds the non-offset elements of a Matrix to avoid issues due to floating point imprecision.
        /// </summary>
        /// <param name="matrix">Matrix to round.</param>
        /// <param name="decimals">Number of decimal places to round to.</param>
        /// <returns>Rounded Matrix.</returns>
        private static Matrix RoundMatrix(Matrix matrix, int decimals)
        {
            return new Matrix(
                Math.Round(matrix.M11, decimals),
                Math.Round(matrix.M12, decimals),
                Math.Round(matrix.M21, decimals),
                Math.Round(matrix.M22, decimals),
                matrix.OffsetX,
                matrix.OffsetY);
        }

        /// <summary>
        /// Implements WPF's Rect.Transform on Silverlight.
        /// </summary>
        /// <param name="rect">Rect to transform.</param>
        /// <param name="matrix">Matrix to transform with.</param>
        /// <returns>Bounding box of transformed Rect.</returns>
        private static Rect RectTransform(Rect rect, Matrix matrix)
        {
            // WPF equivalent of following code:
            // Rect rectTransformed = Rect.Transform(rect, matrix);
            Point leftTop = matrix.Transform(new Point(rect.Left, rect.Top));
            Point rightTop = matrix.Transform(new Point(rect.Right, rect.Top));
            Point leftBottom = matrix.Transform(new Point(rect.Left, rect.Bottom));
            Point rightBottom = matrix.Transform(new Point(rect.Right, rect.Bottom));
            double left = Math.Min(Math.Min(leftTop.X, rightTop.X), Math.Min(leftBottom.X, rightBottom.X));
            double top = Math.Min(Math.Min(leftTop.Y, rightTop.Y), Math.Min(leftBottom.Y, rightBottom.Y));
            double right = Math.Max(Math.Max(leftTop.X, rightTop.X), Math.Max(leftBottom.X, rightBottom.X));
            double bottom = Math.Max(Math.Max(leftTop.Y, rightTop.Y), Math.Max(leftBottom.Y, rightBottom.Y));
            Rect rectTransformed = new Rect(left, top, right - left, bottom - top);
            return rectTransformed;
        }

        /// <summary>
        /// Implements WPF's Matrix.Multiply on Silverlight.
        /// </summary>
        /// <param name="matrix1">First matrix.</param>
        /// <param name="matrix2">Second matrix.</param>
        /// <returns>Multiplication result.</returns>
        private static Matrix MatrixMultiply(Matrix matrix1, Matrix matrix2)
        {
            // WPF equivalent of following code:
            // return Matrix.Multiply(matrix1, matrix2);
            return new Matrix(
                (matrix1.M11 * matrix2.M11) + (matrix1.M12 * matrix2.M21),
                (matrix1.M11 * matrix2.M12) + (matrix1.M12 * matrix2.M22),
                (matrix1.M21 * matrix2.M11) + (matrix1.M22 * matrix2.M21),
                (matrix1.M21 * matrix2.M12) + (matrix1.M22 * matrix2.M22),
                ((matrix1.OffsetX * matrix2.M11) + (matrix1.OffsetY * matrix2.M21)) + matrix2.OffsetX,
                ((matrix1.OffsetX * matrix2.M12) + (matrix1.OffsetY * matrix2.M22)) + matrix2.OffsetY);
        }

        /// <summary>
        /// Implements WPF's Matrix.HasInverse on Silverlight.
        /// </summary>
        /// <param name="matrix">Matrix to check for inverse.</param>
        /// <returns>True if the Matrix has an inverse.</returns>
        private static bool MatrixHasInverse(Matrix matrix)
        {
            // WPF equivalent of following code:
            // return matrix.HasInverse;
            return (0 != ((matrix.M11 * matrix.M22) - (matrix.M12 * matrix.M21)));
        }
    }
}

The style part:

<Style TargetType="common:LayoutTransformer">  
    <Setter Property="Foreground" Value="#FF000000"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="common:LayoutTransformer">
                <Grid x:Name="TransformRoot" Background="{TemplateBinding Background}">
                    <ContentPresenter
                        x:Name="Presenter"
                        Content="{TemplateBinding Content}"
                        ContentTemplate="{TemplateBinding ContentTemplate}"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

Here’s the original code from Silverlight toolkit:

http://silverlight.codeplex.com/SourceControl/changeset/view/74775?ProjectName=silverlight#779405

Enjoy layout transforming in WinRT! :)

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