Change order of wpf graph plots

Question

I'm trying to solve following issue. Let's say I'm sampling data once per second and showing it on the graph. I want to show history of the data, say last 20 plots using the same color with fading. What I do now:
- create 21 plots, say Plots[0]..Plots[20] 
- at meas 1, set Data[0] = data
- set Plots[0] opacity to 1
- at meas 2, set Data[1] = data
- set Plots[1] opacity to 1, Plots[0] opacity to 0.5
- at meas 3, set Data[2] = data
- set Plots[2] opacity to 1, Plots[1] opacity to 0.6, Plots[0] opacity to 0.3
- at meas 21, set Data[20] = data
- set opacity to 0.1..1
// we're fine as of now, here comes the tricky part
- at meas 22 I need to remove the data of meas 0 (stored at Data[0]) and replace it with the new data
- so I set Data[0] = data
- set Plots[0] opacity to 1 (it's the newest result)
- set other plots opacity 0.1..0.9
// and here is the problem: Plots[0] is now at the bottom of the plot stack and is covered by 20 other plots, thus is barely visible
so I somehow need to move Plots[0] to the top of the stack
I've tried removing Plot and Data of the farthest plot and adding creating plot with the most recent data, but it leads to incorrect indices (Plot.Index grows all the time, but Data array stays the same)
Another option would be to fix plots order and opacity in advance, and change data for all plots all the time. But I assume this would be very slow (think of 20-50 copies of the plot with say 1000 points).
So, any bright ideas here?

Answer 1

Idea 1) Pre-allocate all of the fade plots, use BeginInit/EndInit when updating the Data collection, and always apply the newest data to the last plot. In pseudo-code:
    // initial setup
    for( opacity = 0..1 )
        var renderer = new Renderer( opacity )
        graph.Plots.Add( new Plot { Renderer = renderer } )
    // on data update
    graph.BeginInit()
    for( i = 1..graph.Data.Count )
        graph.Data[i - 1] = graph.Data[i] /* shift old data down */
    graph.Data[20] = /* assign new data to the last plot */
    graph.EndInit()
Idea 2) If you just want the historic data visible in the graph (i.e. you do not need to query or interact with the old data through the graph), and if your range is stable, then you could have one plot in the graph and use a PhosphorColorRamp to get the visual fade effect. In pseudo-code:
    // initial setup
    var brush = new SolidColorBrush( C )
    Graph.SetPhosphorMode( brush, Immediate )
    graph.Plots.Add( new Plot { Renderer = new Renderer( brush ) } )
    graph.RenderMode = Raster
    graph.PhosphorColorRamp = new FadeRamp { Color = C, Duration = 20, DurationKind = Frames }
    // on data update
    graph.Data[0] = /* assign new data to first plot */
(Note that the phosphor effect is one of the areas being updated, so the syntax will be changing in the next release of Measurement Studio.)
~ Paul H