Show frame of GIF in Image control

Question

I try to show a single frame of a loaded gif image (from a file) inside an Image control. I have no issue in showing the (full) gif image inside an Image control, but I cannot get the frame to show up. For testing purposes I always try to load frame '0' (the first frame).

XAML:

<Image>
    <Image.Source>
        <BitmapImage x:Name="GifFrame" AutoPlay="False" />
    </Image.Source>
</Image>

I don't really find much information online of how to do this but here and there are some code fragments, some may unfortunately come from WPF and I a m not 100% sure if they can be used also for UWP.

When the image is opened the following "_OnImageOpened" method gets called (_gifStream is the opened gif image, stream has not been closed):

private IRandomAccessStream _gifStream = null;

private async void GifImage_OnImageOpened(object sender, RoutedEventArgs e)
{
    // ...

    uint frameCount = 0;
    if (_gifStream != null)
    {
        var decoder = await BitmapDecoder.CreateAsync(_gifStream);
        frameCount = decoder.FrameCount;

        var frame = await decoder.GetFrameAsync(0);

        // Create frame image
        var pixelData = await frame.GetPixelDataAsync(
            BitmapPixelFormat.Bgra8,
            BitmapAlphaMode.Premultiplied,
            new BitmapTransform(),
            ExifOrientationMode.IgnoreExifOrientation,
            ColorManagementMode.DoNotColorManage
            ).AsTask().ConfigureAwait(false);
        var frameBytes = pixelData.DetachPixelData();
        var memoryStream = new MemoryStream(frameBytes);
        await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
            {
                GifFrame.SetSource(memoryStream.AsRandomAccessStream());
            });
    }
}

When I set the new source (GifFrame.SetSource(...)) the window freezes and nothing happens, I have to kill the process. Before I added the Dispatcher.RunAsync(...) around the setting of the new source I got an exception "The application called an interface that was marshalled for a different thread...".

I don't have any idea what causes this. Maybe I need to convert the bytes to something the image control can understand or maybe the whole pixel data creation is wrong?

Answer 1

Here's one way to achieve what you're looking for:

XAML:

<Page
    x:Class="App1.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    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>
            <Button Content="Open" Click="Button_Click" />
            <Image x:Name="Image" Width="100" Height="100" />
        </StackPanel>
    </Grid>
</Page>

Code:

using System;
using Windows.Graphics.Imaging;
using Windows.Storage;
using Windows.Storage.Pickers;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Media.Imaging;

namespace App1
{
    public sealed partial class MainPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private async void Button_Click(object sender, RoutedEventArgs e)
        {
            var picker = new FileOpenPicker();

            picker.FileTypeFilter.Add(".gif");

            picker.SuggestedStartLocation = PickerLocationId.PicturesLibrary;

            var file = await picker.PickSingleFileAsync();
            if (file == null)
                return;

            var stream = await file.OpenAsync(FileAccessMode.Read);

            var decoder = await BitmapDecoder.CreateAsync(stream);

            var frame = await decoder.GetFrameAsync(0);

            var softwareBitmap = await frame.GetSoftwareBitmapAsync();

            var convert = SoftwareBitmap.Convert(softwareBitmap, BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied);

            var softwareBitmapSource = new SoftwareBitmapSource();

            await softwareBitmapSource.SetBitmapAsync(convert);

            Image.Source = softwareBitmapSource;
        }
    }
}

Result:

Quite convoluted process to say the least ...

Original GIF:

Your actual error is that you're trying to feed SetSource with a raw stream of pixel data, this is not what it expects.