Chart Rendering Reference

Advanced indicators and tools can render directly through IChartOverlayRenderer. This is the preferred API for custom visual layers such as order-flow, volume profile, bar timers, heatmaps, and advanced labels.

Overlay Renderer Interface

public class MyOverlay : Indicator, IChartOverlayRenderer
{
    public ChartRenderPass RenderPass => ChartRenderPass.OverDrawings;
    public bool RenderOnPricePanel => true;

    public void OnRender(IChartRenderContext context)
    {
        // Draw with context methods.
    }
}

Render Passes

Pass	Use case
UnderCandles	Background zones and heatmaps.
OverCandles	Overlays that should sit above bars but below drawings.
OverDrawings	Labels, HUD elements, and top-level overlays.

Render Backends

The render context reports its backend:

• Wpf
• Direct2D
• Skia

Scripts should use the abstract context methods and avoid backend-specific assumptions unless the script explicitly checks context.Backend.

IChartRenderContext

Member	Purpose
Backend	Current render backend.
Pass	Current render pass.
IsMainPane	Whether this context is the main price pane.
PaneId	Current pane identifier.
VisibleFromIndex	First visible bar index.
VisibleToIndex	Last visible bar index.
VisibleCount	Count of visible bars.
CandleWidth	Current candle body width.
CandleGap	Gap between candles.
TickSize	Current instrument tick size.
PriceMin	Visible low scale value for the pane.
PriceMax	Visible high scale value for the pane.
Width	Render area width.
Height	Render area height.

Coordinate Methods

double x = context.GetXByBarIndex(barIndex);
double y = context.GetYByPrice(price);
double price = context.GetPriceByY(y);
int barIndex = context.GetNearestBarIndex(x);

Use these methods instead of duplicating chart scale math.

Drawing Methods

context.DrawLine(start, end, stroke);
context.DrawRectangle(rect, fill, stroke);
context.DrawCircle(center, radius, fill, stroke);
context.DrawText(text, bounds, style);

Basic types:

• ChartPoint
• ChartRect
• ChartPaint
• ChartStroke
• ChartTextStyle

Example

public void OnRender(IChartRenderContext context)
{
    if (!context.IsMainPane || context.VisibleCount <= 0)
        return;

    var paint = new ChartPaint(Colors.DeepSkyBlue, 0.9);
    var stroke = new ChartStroke(paint, 1.5, ChartDashStyle.Solid);

    double y = context.GetYByPrice(Close[0]);
    context.DrawLine(
        new ChartPoint(0, y),
        new ChartPoint(context.Width, y),
        stroke);
}

Performance Rules

• Keep OnRender allocation-light.
• Do not fetch historical data from inside OnRender.
• Precompute expensive values during script updates.
• Use visible indexes to limit loops.
• Use InvalidateChartVisual() when only visuals changed.
• Use InvalidateChart() only when scale/extremum state changed.