Implemented designer scaling

src/Perspex.Application/Designer/Designer.cs

@@ -29,10 +29,17 @@ namespace Perspex.Designer
         
         public static void Init(Dictionary<string, object> shared)
         {
-            Api = new DesignerApi(shared) {UpdateXaml = UpdateXaml};
+            Api = new DesignerApi(shared) {UpdateXaml = UpdateXaml, SetScalingFactor = SetScalingFactor};
             new DesignerApp();
         }
 
+        private static void SetScalingFactor(double factor)
+        {
+            PlatformManager.SetDesignerScalingFactor(factor);
+            if (s_currentWindow != null)
+                s_currentWindow.PlatformImpl.ClientSize = s_currentWindow.ClientSize;
+        }
+
         static Window s_currentWindow;
 
         private static void UpdateXaml(string xaml)

src/Perspex.Application/Designer/DesignerApi.cs

@@ -46,6 +46,11 @@ namespace Perspex.Designer
             get { return (Action<IntPtr>) Get(); }
         }
 
+        public Action<double> SetScalingFactor
+        {
+            set { Set(value);}
+            get { return (Action<double>) Get(); }
+        }
 
     }
 }

src/Perspex.Controls/Platform/PlatformManager.cs

@@ -19,6 +19,7 @@ namespace Perspex.Controls.Platform
             => PerspexLocator.Current.GetService<IPlatformSettings>();
 
         static bool s_designerMode;
+        private static double _designerScalingFactor = 1;
 
         public static IRenderTarget CreateRenderTarget(ITopLevelImpl window)
         {
@@ -33,6 +34,14 @@ namespace Perspex.Controls.Platform
             return Disposable.Create(() => s_designerMode = false);
         }
 
+        public static void SetDesignerScalingFactor(double factor)
+        {
+            _designerScalingFactor = factor;
+        }
+
+        static double RenderScalingFactor => (GetSettings()?.RenderScalingFactor ?? 1)*_designerScalingFactor;
+        static double LayoutScalingFactor => (GetSettings()?.LayoutScalingFactor ?? 1) * _designerScalingFactor;
+
         class RenderTargetDecorator : IRenderTarget
         {
             private readonly IRenderTarget _target;
@@ -53,7 +62,7 @@ namespace Perspex.Controls.Platform
             {
                 var cs = _window.ClientSize;
                 var ctx = _target.CreateDrawingContext();
-                var factor = GetSettings()?.RenderScalingFactor ?? 1;
+                var factor = RenderScalingFactor;
                 if (factor != 1)
                 {
                     ctx.PushPostTransform(Matrix.CreateScale(factor, factor));
@@ -70,7 +79,7 @@ namespace Perspex.Controls.Platform
             private readonly IPopupImpl _popup;
 
             public ITopLevelImpl TopLevel => _tl;
-            double ScalingFactor => GetSettings()?.LayoutScalingFactor ?? 1;
+            double ScalingFactor => LayoutScalingFactor;
 
             public WindowDecorator(ITopLevelImpl tl)
             {

src/Windows/Perspex.Designer/AppHost/HostedAppModel.cs

@@ -11,10 +11,16 @@ namespace Perspex.Designer.AppHost
 {
     public class HostedAppModel : INotifyPropertyChanged
     {
+        private readonly PerspexAppHost _host;
         private IntPtr _nativeWindowHandle;
         private string _error;
         private string _errorDetails;
 
+        internal HostedAppModel(PerspexAppHost host)
+        {
+            _host = host;
+        }
+
         public IntPtr NativeWindowHandle
         {
             get { return _nativeWindowHandle; }
@@ -48,12 +54,26 @@ namespace Perspex.Designer.AppHost
             }
         }
 
+        public IReadOnlyList<double> AvailableScalingFactors => new List<double>() {1, 2, 4, 8};
+
+        public double CurrentScalingFactor
+        {
+            get { return _currentScalingFactor; }
+            set
+            {
+                _currentScalingFactor = value;
+                _host.Api.SetScalingFactor(value);
+            }
+        }
+
         public void SetError(string error, string details = null)
         {
             Error = error;
             ErrorDetails = details;
         }
 
+        double _currentScalingFactor = 1;
+
         public event PropertyChangedEventHandler PropertyChanged;
 
         [NotifyPropertyChangedInvocator]

src/Windows/Perspex.Designer/AppHost/PerspexAppHost.cs

@@ -22,12 +22,13 @@ namespace Perspex.Designer.AppHost
         private string _lastXaml;
         private string _currentXaml;
         private bool _initSuccess;
-        private readonly HostedAppModel _appModel = new HostedAppModel();
+        private HostedAppModel _appModel;
         private Control _window;
 
         public PerspexAppHost(CommChannel channel)
         {
             _comm = channel;
+            _appModel = new HostedAppModel(this);
         }
 
         public void Start()

src/Windows/Perspex.Designer/Comm/CommChannel.cs

@@ -13,7 +13,7 @@ using System.Windows.Threading;
 
 namespace Perspex.Designer.Comm
 {
-    internal class CommChannel : IDisposable
+    class CommChannel : IDisposable
     {
         private readonly BinaryReader _input;
         private readonly BinaryWriter _output;

src/Windows/Perspex.Designer/InProcDesigner/InProcDesignerView.xaml

@@ -4,17 +4,27 @@
              xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
              xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
              xmlns:appHost="clr-namespace:Perspex.Designer.AppHost"
+             xmlns:system="clr-namespace:System;assembly=mscorlib"
              mc:Ignorable="d" 
              d:DesignHeight="300" d:DesignWidth="300" d:DataContext="{d:DesignInstance appHost:HostedAppModel}">
     <DockPanel>
-        <Border x:Name="ErrorPanel" DockPanel.Dock="Bottom" BorderBrush="Red" BorderThickness="3" Padding="3">
-            <StackPanel   Orientation="Horizontal">
-                <TextBlock Text="{Binding Error}" FontSize="16"/>
-                <TextBlock x:Name="DetailsBlock" FontSize="16">
+        <StackPanel Orientation="Horizontal" DockPanel.Dock="Bottom">
+            <ComboBox ItemsSource="{Binding AvailableScalingFactors}" SelectedItem="{Binding CurrentScalingFactor, Mode=TwoWay}">
+                <ComboBox.ItemTemplate>
+                    <DataTemplate DataType="{x:Type system:Double}">
+                        <TextBlock><Run Text="{Binding .}"/>00%</TextBlock>
+                    </DataTemplate>
+                </ComboBox.ItemTemplate>
+            </ComboBox>
+            <Border x:Name="ErrorPanel" BorderBrush="Red" BorderThickness="3" Padding="3">
+                <StackPanel   Orientation="Horizontal">
+                    <TextBlock Text="{Binding Error}" FontSize="16"/>
+                    <TextBlock x:Name="DetailsBlock" FontSize="16">
                 <Run> (</Run><Hyperlink Click="Hyperlink_OnClick">View details</Hyperlink><Run>)</Run>
-                </TextBlock>
-            </StackPanel>
-        </Border>
+                    </TextBlock>
+                </StackPanel>
+            </Border>
+        </StackPanel>
         <WindowsFormsHost x:Name="WindowHostControl"/>
     </DockPanel>
 </UserControl>