Annotations

An annotation is a shape or a text placed on the chart: a box around a session, a horizontal level, a label. Unlike a series, it is not tied to one bar.

Creating an annotation

Create it, set it, add it to a group. From then on it is drawn.

var box = VAn.CreateAnnotation(AnnotationType.Rectangle);
box.X = firstIndex + 0.5;
box.X2 = lastIndex + 1.5;
box.Y = high;
box.Y2 = low;
box.LineColor = BoxColor;
box.BackColor = BoxColor.WithOpacity(25);
VAn.AddAnnotation(group, box);

Common types: Line, Rectangle, Text, HorizontalLine, VerticalLine, HorizontalRay, Ellipse, Triangle, ArrowUp, ArrowDown, Diamond. To change an annotation later, set its properties again. To remove it, call group.RemoveAnnotation(annotation).

Coordinates

By default the coordinates are absolute: a bar and a value of the Y axis.

Y, Y2 are prices (or values of the area the annotation is in).
X, X2 are positions on the bars: the bar of index i is at i + 1. A bar is one unit wide, from i + 0.5 to i + 1.5. A value beyond the last bar is in the future.

Other coordinate types, set with CoordinateXType and CoordinateYType:

Type	Meaning
`Absolute`	bars and values (the default)
`Relative`	a position in the chart area, from `0` to `1`: the annotation stays in place while the chart scrolls
`Pixel`	pixels from the edge of the chart area

label.CoordinateXType = CoordinateTypeEnum.Relative;
label.CoordinateYType = CoordinateTypeEnum.Relative;
label.X = 0.02;
label.Y = 0.95;

Groups

Annotations are kept in groups. The indicator has two of its own:

Group	Use
`IndVars.Ann_List`	the annotations of the indicator
`IndVars.FrontAnnList`	annotations drawn on the foreground, over the bars and the other indicators

A group holds either annotations or other groups, not both. For a few annotations, add them directly to IndVars.Ann_List. When you have different kinds, create one group per kind:

public override void OnLoad()
{
    boxes = VAn.CreateAnnGroup();
    labels = VAn.CreateAnnGroup();
    IndVars.Ann_List.AddGroup(boxes);
    IndVars.Ann_List.AddGroup(labels);
}

The chart empties the groups of the indicator before every calculation, so create your groups and your fixed annotations in OnLoad.

Which area

An annotation is drawn in the main area of the chart (the price) unless you say otherwise:

annotation.Area = ChartArea;          // the area the user placed the indicator in
annotation.Area = ChartAreaRef.Main;  // the price area (the default)

Text

Property	Meaning
`Text`	the text. A `Text` annotation is placed at `X`, `Y`
`ForeColor`	color of the text
`FontSize`, `FontBold`	font
`TextAlign`	alignment relative to the position
`BackColor`, `LineColor`	background and border

Performance

Annotations which change often are cheap: only what changed is redrawn or sent. What costs is their number. When an indicator creates annotations for every bar, remove the old ones or limit how many sessions it draws, as the Session Range Box example does.

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Creating an annotation

Coordinates

Groups

Which area

Text

Performance

​Creating an annotation

​Coordinates

​Groups

​Which area

​Text

​Performance

Creating an annotation

Coordinates

Groups

Which area

Text

Performance