Table of Contents

Annotations

Arrow annotations with background

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .WithTitle("Annotation Enhancements")
        .Plot(x, y, line => { line.Label = "Data"; })
        .Annotate("Peak", 8, 8.9, ann =>
        {
            ann.ArrowTargetX = 8;
            ann.ArrowTargetY = 8.9;
            ann.ArrowStyle   = ArrowStyle.FancyArrow;
            ann.BackgroundColor = Colors.White;
        })
        .Annotate("Rotated label", 2, 4.5, ann =>
        {
            ann.Rotation  = -30;
            ann.Alignment = TextAlignment.Center;
        }))
    .Save("annotations.svg");

Annotations

Horizontal reference line

Mark thresholds, targets, or boundaries:

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "Data")
        .AxHLine(5.0, l =>
        {
            l.Color = Colors.Red;
            l.LineStyle = LineStyle.Dashed;
            l.LineWidth = 1.5;
            l.Label = "Threshold";
        })
        .WithLegend())
    .Save("hline.svg");

Vertical reference line

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y)
        .AxVLine(5.0, l =>
        {
            l.Color = Colors.Green;
            l.LineStyle = LineStyle.DashDot;
            l.Label = "Event";
        })
        .WithLegend())
    .Save("vline.svg");

Shaded span regions

Highlight a range on the axis:

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "Signal")
        // Vertical span: highlight an X range
        .AxVSpan(3.0, 6.0, s =>
        {
            s.Color = Colors.Yellow;
            s.Alpha = 0.3;
            s.Label = "Active period";
        })
        // Horizontal span: highlight a Y range
        .AxHSpan(4.0, 7.0, s =>
        {
            s.Color = Colors.LightBlue;
            s.Alpha = 0.2;
            s.Label = "Target range";
        })
        .WithLegend())
    .Save("spans.svg");

Multiple reference lines

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "Price")
        .AxHLine(20, l => { l.Color = Colors.Green; l.LineStyle = LineStyle.Dashed; l.Label = "Support"; })
        .AxHLine(70, l => { l.Color = Colors.Red;   l.LineStyle = LineStyle.Dashed; l.Label = "Resistance"; })
        .AxVLine(5,  l => { l.Color = Colors.Gray;  l.LineStyle = LineStyle.Dotted; l.Label = "Earnings date"; })
        .WithLegend(LegendPosition.UpperLeft))
    .Save("multi_ref.svg");

Threshold convenience

Threshold(...) is a single-call shortcut that composes a dashed reference line and a shaded breach-zone span in one step. Use it instead of manually calling AxHLine + AxHSpan when you only care about marking a breach boundary.

double[] x = Enumerable.Range(0, 100).Select(i => (double)i).ToArray();
double[] y = x.Select(v => 50 + 30 * Math.Sin(v * 0.15)).ToArray();

// Shade everything ABOVE 70 (overbought zone)
Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "Signal")
        .Threshold(70.0, Orientation.Horizontal, ThresholdBreach.Above,
            color: Colors.Red, label: "Overbought")
        .WithLegend())
    .Save("threshold_above.svg");

Shade the below side for a support floor:

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "Signal")
        .Threshold(30.0, Orientation.Horizontal, ThresholdBreach.Below,
            color: Colors.Tab10Green, label: "Oversold")
        .WithLegend())
    .Save("threshold_below.svg");

Stack both to create a corridor with upper and lower bounds:

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y, s => s.Label = "RSI")
        .Threshold(70.0, Orientation.Horizontal, ThresholdBreach.Above, Colors.Red,   "Overbought")
        .Threshold(30.0, Orientation.Horizontal, ThresholdBreach.Below, Colors.Tab10Green, "Oversold")
        .SetYLabel("RSI")
        .WithLegend())
    .Save("threshold_corridor.svg");

Vertical thresholds work identically — Orientation.Vertical marks a constant X:

// Shade everything to the RIGHT of an event date
DateTime eventDate = new DateTime(2026, 6, 15);

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(dates, prices, s => s.Label = "Price")
        .SetXDateAxis()
        .Threshold(eventDate.ToOADate(), Orientation.Vertical, ThresholdBreach.Above,
            color: Colors.Tab10Orange, label: "Event")
        .WithLegend())
    .Save("threshold_vertical.svg");

Threshold parameters

Parameter Type Default Description
value double (required) Threshold position in data coordinates.
orientation Orientation (required) Horizontal = constant Y line; Vertical = constant X line.
breach ThresholdBreach (required) Above shades above/right of the line; Below shades below/left.
color Color? null Colour for both the dashed line and the span fill. null = renderer cycle colour.
label string? null Annotation text placed at the threshold value. null = no annotation.

The dashed line is a ReferenceLine (LineStyle.Dashed, configurable afterwards via axes.ReferenceLines). The span extends to double.MaxValue (Above) or double.MinValue (Below) so it always reaches the visible plot boundary.

Combining annotations with math text

Plt.Create()
    .AddSubPlot(1, 1, 1, ax => ax
        .Plot(x, y)
        .Annotate(@"$R^{2} = 0.97$", 3, 7, ann =>
        {
            ann.BackgroundColor = Colors.White;
            ann.FontSize = 14;
        })
        .Annotate(@"$\frac{\partial f}{\partial x} = 0$", 8, 3, ann =>
        {
            ann.ArrowTargetX = 8;
            ann.ArrowTargetY = y[8];
            ann.ArrowStyle = ArrowStyle.FancyArrow;
        }))
    .Save("math_annotations.svg");

Fluent API reference

Method Parameters Description
.Annotate(text, x, y, cfg?) text, position Text annotation at (x, y)
.Annotate(text, x, y, arrowX, arrowY, cfg?) + arrow target Text with arrow pointing to target
.AxHLine(y, cfg?) y position Horizontal reference line
.AxVLine(x, cfg?) x position Vertical reference line
.AxHSpan(yMin, yMax, cfg?) y range Horizontal shaded band
.AxVSpan(xMin, xMax, cfg?) x range Vertical shaded band
.Threshold(value, orientation, breach, color?, label?) value, orientation, breach Dashed reference line + shaded breach span

Annotation properties

Property Type Description
ArrowTargetX/Y double Arrow endpoint
ArrowStyle ArrowStyle FancyArrow, Simple, ...
BackgroundColor Color Text background
FontSize double Font size
Rotation double Text rotation in degrees
Alignment TextAlignment Left, Center, Right

ReferenceLine properties

Property Type Description
Color Color Line color
LineStyle LineStyle Solid, Dashed, Dotted, DashDot
LineWidth double Line width
Label string Legend label

SpanRegion properties

Property Type Description
Color Color Fill color
Alpha double Transparency (0–1)
Label string Legend label
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