Override one virtual method to control how a tool responds to dragging — for example, pinning a horizontal line to a single price so it never drifts sideways in time.

What it is

When the user drags a placed tool, the host calls Move(TimeSpan dTime, double dPrice) with the change in time and price for the drag. The default DrawingToolBase.Move shifts every anchor by both deltas — exactly right for a free-floating shape like a trend line or rectangle:

DrawingToolBase.cspublic virtual void Move(TimeSpan dTime, double dPrice)
{
    for (int i = 0; i < AnchorCount; i++)
    {
        var a = Anchors[i];
        SetAnchor(i, new DrawingAnchor(a.Time + dTime, a.Price + dPrice));
    }
}

When a tool has a geometric constraint — a horizontal line that should only change price, a vertical line that should only change time — override Move and apply just the deltas that make sense. Commit each new anchor with SetAnchor.

A horizontal line: price only

A horizontal line keeps each anchor's time and adds only the price delta, so dragging it up or down moves the level but never slides it through time.

HorizontalLine.cs[DrawingToolMetadata("Horizontal Line", Category = "Lines", IconKey = "HorizontalLine", AnchorCount = 1)]
public sealed class HorizontalLine : DrawingToolBase
{
    public HorizontalLine() : base(anchorCount: 1) { }

    public override void Move(TimeSpan dTime, double dPrice)
    {
        var a = Anchors[0];
        SetAnchor(0, new DrawingAnchor(a.Time, a.Price + dPrice));   // price only
    }

    public override void OnRender(IDrawingToolRenderContext ctx)
    {
        double y = ctx.Viewport.PriceToPixelY(Anchors[0].Price);
        ctx.Renderer.DrawLine(ctx.PlotArea.X, y, ctx.PlotArea.Right, y, Color, LineWidthPx);
        if (ctx.IsSelected) ctx.DrawHandle((ctx.PlotArea.X + ctx.PlotArea.Right) / 2, y);
    }

    public override bool HitTest(double px, double py, IDrawingToolRenderContext ctx, double tol = 6)
    {
        double y = ctx.Viewport.PriceToPixelY(Anchors[0].Price);
        return DrawingGeometry.DistanceToHorizontalLine(py, y) <= tol;
    }
}

A vertical line: time only

The mirror image keeps each anchor's price and adds only the time delta. Pair it with the DrawingAnchor.TimeOnly factory at placement so the unused price stays a sentinel.

VerticalLine.cspublic override void Move(TimeSpan dTime, double dPrice)
{
    var a = Anchors[0];
    SetAnchor(0, new DrawingAnchor(a.Time + dTime, a.Price));   // time only
}