WPF News Ticker - timing issues

[Borvik]

I'm working on a news ticker application as part of a company dashboard.

I'm basing the ticker on RumorMill ticker found

http://codefreezer.com/codedetail.php?article=64.

Instead of scrolling horizontally, mine is scrolling vertically, and because there may be a small number of items they get removed as soon as they clear the display area - which then can get them put back into the queue again (assuming it wasn't removed from the database).

My issue is with the timing/speed of the news items. Some items seem to be scrolling faster than others - with the chance that some could overlap.

I've been operating with the following equations:
s = d/t (general speed formula)
w = window height
h = item height
t = specified time on screen
t₁ = actual time to target

The animation moving the item from window height (item clipped below the panel) to the item's height above the window.
w/t = s = (w+h)/t₁
(w+h)/s = t₁

Here is the code for the animation:

    Private Sub AnimateMove(ByVal e As FrameworkElement)
        ' Max Width/Height set in calling routine based on orientation
        '  of the scroll.
        e.Measure(New Size(e.MaxWidth, e.MaxHeight))
        'e.Measure(New Size(Double.PositiveInfinity, Double.PositiveInfinity))
        Dim r As New Rect(e.DesiredSize)
        e.Arrange(r)

        Dim [from] As Double = If(_orientation = Controls.Orientation.Horizontal, Container.ActualWidth, Container.ActualHeight)
        Dim elSize As Double = If(_orientation = Controls.Orientation.Horizontal, e.ActualWidth, e.ActualHeight)
        Dim [to] As Double = 0 - elSize

        Dim windowSpeed As Double = ([from] / Speed.TotalSeconds)
        Dim newTime As Double = (([from] + elSize) / windowSpeed)
        Dim actualDuration As New TimeSpan(0, 0, Convert.ToInt32(newTime))
        Dim nextFire As Integer = Convert.ToInt32((elSize + SeperatorSize) / windowSpeed)

        'This is what triggers the next item to be added to the container - and then animated with this subroutine
        displayTimer.Stop()
        displayTimer.Interval = New TimeSpan(0, 0, nextFire)
        displayTimer.Start()

        Dim ani As New TaggedDoubleAnimation
        ani.From = [from]
        ani.To = [to]
        ani.Duration = New Duration(actualDuration)
        ani.TargetElement = e
        Dim depProp As DependencyProperty = If(_orientation = Controls.Orientation.Horizontal, TranslateTransform.XProperty, TranslateTransform.YProperty)
        AddHandler ani.Completed, AddressOf ani_Completed

        Dim trans As New TranslateTransform()
        e.RenderTransform = trans
        trans.BeginAnimation(depProp, ani, HandoffBehavior.Compose)
    End Sub

Any ideas on what might be causing the timing to be off?

 

[stravis]

The height of your strings is different and therefore they are moving at different speeds.

 

[Borvik]

According to my calculations I am compensating for that.

I first calculate the speed based on the given duration for the height of the container:

Dim windowSpeed As Double = ([from] / Speed.TotalSeconds)

I then use that to calculate the new duration for the specific item from the speed (which stays the same from each run to the next - verified) and the container height + the item height:

Dim newTime As Double = (([from] + elSize) / windowSpeed)

That time is what is used as the actual duration of the animation - keeping the speed constant between the strings.

 

[Borvik]

I figured it out. It was a rounding issue. All the calculations use doubles for increased precision, but then stick that double into the seconds parameter of a timespan (an Integer). By multiplying it by 1000, and placing it in the milliseconds parameter it increased the precision of the timespan, and solved the issue.