Render UIElement to PNG

MainPage.xaml

<Page
  x:Class="BitmapToPNGTest.MainPage"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:local="using:BitmapToPNGTest"
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="d"
  Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

  <Grid>
    <StackPanel Orientation="Vertical">
      <Button Content="Render hidden UIElement to PNG" Click="RenderHiddenElement_Click" HorizontalAlignment="Center"
        Padding="20" />
      <Button Content="Render visible UIElement to PNG" Click="RenderVisibleElement_Click" HorizontalAlignment="Center"
        Padding="20" />
    </StackPanel>

    <local:TestControl x:Name="VisibleTestControl" Width="300" Height="300" VerticalAlignment="Bottom" Margin="0 0 0 40"  />

  </Grid>
</Page>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Foundation;
using Windows.Foundation.Collections;
using Windows.Graphics.Imaging;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Data;
using Windows.UI.Xaml.Input;
using Windows.UI.Xaml.Media;
using Windows.UI.Xaml.Media.Imaging;
using Windows.UI.Xaml.Navigation;

// The Blank Page item template is documented at http://go.microsoft.com/fwlink/?LinkId=391641

namespace BitmapToPNGTest
{
    /// <summary>
    /// An empty page that can be used on its own or navigated to within a Frame.
    /// </summary>
    public sealed partial class MainPage : Page
    {
        public MainPage()
        {
            this.InitializeComponent();
            this.NavigationCacheMode = NavigationCacheMode.Required;
        }


        private async void RenderHiddenElement_Click(object sender, RoutedEventArgs e)
        {
          // create UIElement
          FrameworkElement element = new TestControl();

          int width = 300;
          int height = 300;

          element.Width = width;
          element.Height = height;
          element.UpdateLayout();
          element.Measure(new Size(width, height));
          element.UpdateLayout();
          element.Arrange(new Rect(0, 0, width, height));
          element.UpdateLayout();
          element.InvalidateArrange();
          element.InvalidateMeasure();
          element.UpdateLayout();

          var bitmap = new RenderTargetBitmap();

          await bitmap.RenderAsync(element);
          await SavePngAsync(bitmap);
        }


        private async void RenderVisibleElement_Click(object sender, RoutedEventArgs e)
        {
          // get UIElement
          FrameworkElement element = VisibleTestControl;

          int width = 300;
          int height = 300;

          element.Width = width;
          element.Height = height;
          element.UpdateLayout();
          element.Measure(new Size(width, height));
          element.UpdateLayout();
          element.Arrange(new Rect(0, 0, width, height));
          element.UpdateLayout();
          element.InvalidateArrange();
          element.InvalidateMeasure();

          var bitmap = new RenderTargetBitmap();

          await bitmap.RenderAsync(element);
          await SavePngAsync(bitmap);
        }


        private async Task SavePngAsync(RenderTargetBitmap renderTargetBitmap)
        {
          WriteableBitmap writeableBitmap = new WriteableBitmap((int)renderTargetBitmap.PixelWidth, (int)renderTargetBitmap.PixelHeight);

          using (Stream stream = writeableBitmap.PixelBuffer.AsStream())
          {
            BitmapEncoder encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.PngEncoderId, stream.AsRandomAccessStream());
            byte[] pixels = (await renderTargetBitmap.GetPixelsAsync()).ToArray();

            encoder.SetPixelData(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Straight, (uint)renderTargetBitmap.PixelWidth, (uint)renderTargetBitmap.PixelHeight, 96.0, 96.0, pixels);

            await encoder.FlushAsync();
          }
        }
    }
}

TestControl.xaml

<UserControl
  x:Class="BitmapToPNGTest.TestControl"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  xmlns:local="using:BitmapToPNGTest"
  xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
  xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
  mc:Ignorable="d"
  d:DesignHeight="400"
  d:DesignWidth="400">

  <Grid Background="#00b4a8">
    <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center"
      Foreground="White" Text="TestControl" FontSize="28" />
  </Grid>
</UserControl>