Image scaling related crashes on 1080p devices #wpdev

Back in March one of the 1Shot camera app users emailed me stating that the app crashes when using he uses digital zoom on Lumia 1520. I couldn’t reproduce the issue on my 1020. I then borrowed a friend’s 1520 and hmm sure I could reproduce it but I couldn’t catch the exception.

So we left it at that.. fast forward on Friday I get a mail back from chap in question and he states that he’s running latest greatest version of preview and the freaky crash is still happening. Luckily I have the 1520 at my desk and decided to put it to good use over the weekend.

So I put VS configuration in Debug mode and I set VS to catch all thrown exceptions. Run app and swipe left right and top bottom and every so often the app crashes.. no exception being caught.. the app just disappears and we are back to home screen. The only clue was the output of debug mode.. The program ‘[4880] AgHost.exe’ has exited with code -1073741819 (0xc0000005) ‘Access violation’.

The sad reality, the debug output is littered with messages starting ‘AgHost.exe’ (CoreCLR: Silverlight AppDomain): A quick check on the net showed that AgHost.exe is used to manage access through identity verification.. great. The error code wasn’t particularly useful either.

In this particular case, the error only occurred when zooming in. My implementation of digital zoom was scaling the preview image for the live view. The only action associated with crash was zooming in and out. As it happens, I detect manipulation delta and compute scale..

private void LivePreviewTapTarget_ManipulationDelta(object sender, System.Windows.Input.ManipulationDeltaEventArgs e)
{
    if (!this.viewModel.CaptureInitiated && AppSettings.InternalAppSettings.DragZoom)
    {
        SetDragToScale(e.CumulativeManipulation.Translation);
        e.Handled = true;
    }
}

void SetDragToScale(System.Windows.Point pScale)
{
    double x = Math.Abs(pScale.X);
    double y = Math.Abs(pScale.Y);

    double manipulation = x > y ? pScale.X : pScale.Y;

    bool zoomOut = manipulation >= 0 ? false : true;

    double scale = (this.viewModel.HasHighResolutionCamera ? 0.01 : 0.005) * Math.Sqrt(Math.Pow(x, 2) + Math.Pow(y, 2));

    if (zoomOut)
        this.viewModel.ViewScale = initialScale + scale;
    else
        this.viewModel.ViewScale = initialScale - scale;

    System.Diagnostics.Debug.WriteLine("zoomout {0}, scale {1}", zoomOut, scale);
}

My initial thought was that it being a newer SoC, the Xaml Renderer was somehow being proactive somewhere and getting itself in a mess.

Test 1: show less frames and show larger jumps so there is less rendering. For High Res camera I used constant of 0.01.. increase it to 0.05.

The resultant build crashed very very fast. hardly took a swipe or two to head back to home screen.

So I wanted to try the reverse but by laptop decided to shutdown and I was too knackered to continue yesterday.
Earlier today I had a chat with Bill Reiss.. he mentioned that he had some problems with 1520 too and that it had something to do with how large the image becomes on 1080p screen.

So I decided to continue where I left yesterday but with a reduction only for 1080p devices.
Test 2: reduce the multiplication constant to 0.0015 if a 1080p device is detected.
Result: Significant reduction in crashes.. I can still get it to crash but not that often. Here is the changed version

int DeviceScaleFactor = -1;
private void GetScaleFactor()
{
    object physicalScreenResolutionObject;

    if (DeviceExtendedProperties.TryGetValue("PhysicalScreenResolution", out physicalScreenResolutionObject))
    {
        var physicalScreenResolution = (Size)physicalScreenResolutionObject;

        DeviceScaleFactor = (int)(physicalScreenResolution.Width / 4.8);
    }
    else
    {
        DeviceScaleFactor = Application.Current.Host.Content.ScaleFactor;
    }
}

void SetDragToScale(System.Windows.Point pScale)
{
    double x = Math.Abs(pScale.X);
    double y = Math.Abs(pScale.Y);

    double manipulation = x > y ? pScale.X : pScale.Y;

    bool zoomOut = manipulation >= 0 ? false : true;

    if (this.DeviceScaleFactor == -1)
    {
        this.GetScaleFactor();
    }

    double scale = (this.viewModel.HasHighResolutionCamera ? 0.01 : 0.005) * Math.Sqrt(Math.Pow(x, 2) + Math.Pow(y, 2));

    if (DeviceScaleFactor == 225)
    {
        scale = 0.0015 * Math.Sqrt(Math.Pow(x, 2) + Math.Pow(y, 2));
    }

    if (zoomOut)
        this.viewModel.ViewScale = initialScale + scale;
    else
        this.viewModel.ViewScale = initialScale - scale;

    System.Diagnostics.Debug.WriteLine("zoomout {0}, scale {1}", zoomOut, scale);
}

if the Device scale factor is 225, its a 1080p device and one should exercise caution.

Super Duper All in one VisibilityConverter for #wpdev

On the 4th of July I blogged about simple visibility converters to toggle visibility. Of course I used two converters then.. one Visibility and another inverse aka Invisibility.

I also said that some clever people might tell me that its possible to do both in a single converter. Whilst that is true, no one did so apparently no one really reads or cares 😐 Coding4Fun toolkit has a converter than exposes Inverted property but my idea was to be able to use the same converter by pass a parameter.

So here’s what I did

 

public class VisibilityConverter : IValueConverter
{
    public enum Mode
    {
        Default,
        Inverted,
    }

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        Visibility returnVisibility = Visibility.Visible;
        Mode mode = Mode.Default;
        try
        {
            if(parameter != null)
                mode = (Mode)Enum.Parse(typeof(Mode), (string)parameter, true);
        }
        catch 
        {
            mode = Mode.Default;
        }

        if (value == null)
        {
            returnVisibility = Visibility.Collapsed;
        }
        else if(value is bool)
        {
            bool bVal = (bool)value;
            if (!bVal)
                returnVisibility = Visibility.Collapsed;
        }
        else if (value is string)
        {
            string itemVal = value as String;

            if (String.IsNullOrWhiteSpace(itemVal))
                returnVisibility = Visibility.Collapsed;
        }
        else if (value is IList)
        {
            IList objectList = value as IList;
            if (objectList == null || objectList.Count == 0)
                returnVisibility = Visibility.Collapsed;    
        }

        if (mode == Mode.Inverted)
            return returnVisibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
        else
            return returnVisibility;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

and how do I use it ? well this is how

<TextBlock Text="{Binding Review}" Visibility="{Binding Review, Converter={StaticResource VisibilityConverter}}" TextWrapping="Wrap" Style="{StaticResource PhoneTextNormalStyle}" Grid.Column="0" Grid.Row="1" Grid.ColumnSpan="2"/>
<TextBlock Text="(rating only)" Visibility="{Binding Review, Converter={StaticResource VisibilityConverter}, ConverterParameter=Inverted}" Foreground="{StaticResource PhoneSubtleBrush}" TextWrapping="Wrap" Style="{StaticResource PhoneTextNormalStyle}" Grid.Column="0" Grid.Row="1" Grid.ColumnSpan="2"/>

I could pass Default parameter or just leave it out and it defaults to normal behaviour. If I however pass Inverted parameter to the converter, it inverts the behaviour. Bingo.

Now waiting for the next clever people to tell me that I am using parameter designed for something else 🙂

LongListSelector and scroll to top #wpdev

I pulled out my Marauder’s Map, tapped my wand and said “I solemnly swear I’m up to no good”. Bang Visual Studio opens up and I am back to playing with Cineworld app. I know a few users hate my ever so frequent updates but I use the app and I need change 🙂

so I recently got to putting a DatePicker and LongListSelector for being able to “Show by date” film listings. It all worked – well mostly worked until I realised that LongListSelector was scrolled all the way to the bottom. I wonder why..

Of course there is no SelectedIndex I could magically set so did a quick search on the net.. StackOverflow usually has all the answers to “the life, the universe and everything else” but it didn’t really have one for this question.

There was a note saying use UpdateLayout and then ScrollTo and setting it to ItemSource’s first child did the trick for WP8 but not for WP7.

var dataLetter = cd.GetGroupForDate(userSelection); // get the grouped list of films

FilmsForSelectedDate.Clear(); // clear the bound observable collection

foreach (var entry in dataLetter)
    FilmsForSelectedDate.Add(entry);

lstShowByDate.UpdateLayout(); // call updatelayout

if (FilmsForSelectedDate.Count != 0)
    lstShowByDate.ScrollTo(FilmsForSelectedDate[0]); // set scroll to first group in the list

The problem I realised was that the first group in the LLS had zero items i.e. it was not being shown. This affected WP7 toolkit LongListSelector but not the native WP8 LongListSelector

var dataLetter = cd.GetGroupForDate(userSelection);

FilmsForSelectedDate.Clear();

foreach (var entry in dataLetter)
    FilmsForSelectedDate.Add(entry);

lstShowByDate.UpdateLayout();

if (FilmsForSelectedDate.Count != 0)
    lstShowByDate.ScrollTo(FilmsForSelectedDate.First(g => g.HasItems));

So the solution as shown above is, find the group that has items and set scroll to that element.

Mischief managed!