Plotting linear functions on ScatterPlot

[faeriedust]

I have a XamlCartesianChart with several XamlScatterSeries on it, but I would like to plot some boundary lines to help visualize why points are showing up in certain areas.

I was able to draw a vertical line using XamlRectangularSection, but I'm confused on the best way to draw diagonal ones.

What I have:

What I want (created pic using paint):

I tried adding a XamlLineSeries with 2 points, but then it zooms the graph based on the 2 selected points, etc, and it seemed very messy.
I'm wondering the best place to start looking if I want to just plot a line given an x and y intercept on top of the Scatter Series.

[faeriedust]

let getBoundaryPoints (data:Point seq) (interceptLine: InterceptLine) =
            
        let xs = data |> Seq.map _.X
        let ys = data |> Seq.map _.Y
        
        let minX= (xs |> Seq.min |> double) - 1.0
        let maxX= (xs |> Seq.max |> double) + 1.0
        let minY = (ys |> Seq.min |> double) - 1.0
        let maxY = (ys |> Seq.max |> double) + 1.0
        
        let eiIntercept = double(interceptLine.YIntercept)
        let siIntercept = double(interceptLine.XIntercept)
        
        let slope = (xIntercept/yIntercept) * -1.0
        
        let pointA = ObservablePoint(minX, (slope*minX) + yIntercept)
        let pointB = ObservablePoint(maxX, (slope*maxX) + yIntercept)
        let pointC = ObservablePoint((minY-yIntercept)/slope,minY)
        let pointD = ObservablePoint((maxY-yIntercept)/slope,maxY)
        
        [|pointA;pointB;pointC;pointD|]
        |> Seq.filter(fun p -> (p.X + 1.0) >= minX)
        |> Seq.filter(fun p -> (p.X - 1.0) <= maxX)
        |> Seq.filter(fun p -> (p.Y + 1.0) >= minY)
        |> Seq.filter(fun p -> (p.Y - 1.0) <= maxY)
        |> Seq.toArray

<lvc:XamlRectangularSection
    Xi="{Binding MinXRed}"
    Xj="{Binding MinXRed}"
    Stroke="{StaticResource RedLine}"
    ZIndex="102"/>

<lvc:XamlLineSeries
    Stroke="{StaticResource RedLine}"
    Fill="{x:Null}"
    LineSmoothness="0"
    IsHoverable="False"
    GeometrySize="0"
    ZIndex="102"
    Values="{Binding RedBoundaryPoints}"/>

With the result:

It felt rather goofy though.

It could be cool if there was way to determine which series are used for zoom determination or just being able to plot a function.

[faeriedust]

Moving the boundary lines via avalonia bindings results in some very odd phantom points in the lines. I'll report a bug later, but it looks really goofy.