Indicator with custom painting (GDI)

Draw any graphical objects on the chart using the GDI+ library

Introduction

In this topic, we will show you how to use a really great possibility of scripts in Quantower — a custom painting on the Chart. You can draw anything you need via GDI+ — a graphical subsystem of Windows. In C# all features from GDI+ are encapsulated in class Graphics. It is a set of functions allowing to create graphical primitives and splines using brushes and pens, Images, etc. More information you can find on the Microsoft documentation site.

Access Graphics object

Let's start. To get access to Graphics object of the chart you need to override OnPaint method and use Hdc value from its parameters:

public override void OnPaintChart(PaintChartEventArgs args)
{
    // Use args.Hdc to create Graphics which give us acces to chart canvas
    Graphics gr = Graphics.FromHdc(args.Hdc);                        

    // Add your custom drawings here...
}

That's all - now you have full access to chart's canvas and can draw anything you want. For drawing in C# you need to call special methods with graphical parameters: coordinates, color, width, etc.:

public override void OnPaintChart(PaintChartEventArgs args)
{
    Graphics gr = Graphics.FromHdc(args.Hdc);

    // Draw a line using predefined Red pen
    gr.DrawLine(Pens.Red, 100,100,200,200);

    // Draw a rectangle using predefined Blue pen
    gr.DrawRectangle(Pens.Blue, 250, 100, 100, 100);

    // Fill a rectangle using predefined yellow brush
    gr.FillRectangle(Brushes.Yellow, 400, 100, 100, 100);            

    // Create a custom pen and use it for drawing
    Pen myPen = new Pen(Color.Green, 3);
    gr.DrawRectangle(myPen, 50, 50, 500, 200);
}

If we build this indicator - we can see the result on the chart window:

Drawing directly on the chart

Drawing a simple text

Let's try to draw a text — it is very similar. We need to specify text, font, and coordinates:

public override void OnPaintChart(PaintChartEventArgs args)
{
    Graphics gr = Graphics.FromHdc(args.Hdc);

    // Draw the text with specified font and color
    gr.DrawString("An examle if drawing text...", new Font("Arial", 20), Brushes.Red, 100, 100);    
}

Build this and check your chart:

Drawing a text

Market depth levels on chart

Ok, it is interesting but quite useless. Let's do something more serious — for example, display all levels of market depth on the chart. This is source code:

protected override void OnInit()
{
    // Subscribe for level 2 quotes            
    this.Symbol.Subscribe(SubscribeQuoteType.Level2);
}

public override void OnPaintChart(PaintChartEventArgs args)
{
    Graphics gr = Graphics.FromHdc(args.Hdc);

    // Create a font
    Font font = new Font("Arial", 10);

    // Request a current sorting bids
    List<Level2Item> sortedBids = this.Symbol.Bids.GetSortedList();

    // Draw bids
    for (int i = 0; i < sortedBids.Count; i++)
        gr.DrawString(sortedBids[i].Quote.Price.ToString(), font, Brushes.LightGray, 20, 23 * i + 30);

    // Request a current sorting asks
    List<Level2Item> sortedAsks = this.Symbol.Asks.GetSortedList();

    // Draw asks
    for (int i = 0; i < sortedAsks.Count; i++)
        gr.DrawString(sortedAsks[i].Quote.Price.ToString(), font, Brushes.LightGray, 100, 23 * i + 30);     
}

And this is how our chart looks now. You can compare results with Market Depth panel in Quantower:

Display bids and asks on the chart

It is a great possibility of chart features extending, isn't it? You can add your own Info Window, Track Cursor or even Volume Analysis visualization. There are no limitations in our API, only your fantasy.