Steema Central

Posted: **Wed Apr 27, 2005 12:45 pm**

I have Series1 (TCandleSeries) & Series2(TLIneSeries). Series1 is displayed as a High-Low-Close bar. I need to plot arrows at points where the Series2 intersects Series1. Given that I know the series index at which the intersection occurs, how do I compute x0,y0,x1 & y1 coordinates - I believe they are screen coordinates.

I wish to draw the arrow above the high of the high-low-close bar or below the low of the high-low-close bar. Also how do I ensure that arrows for all other non-intersecting points are not visible. Do I make the arrow color same as chart background color ?

Will appreciate help/suggestions.

Regards,

Satish

Posted: **Thu Apr 28, 2005 11:50 am**

Hi.

If both series share the same x values then if you know Series2 (or Series1) ValueIndex, you also know intersection x and y value. Example:

Code: Select all

var x,y: double;
begin
  x := Series2.XValues[Index];
  y := Series2.YValues[Index];
end;

On the other hand, if you want to transform real x,y coordinates back to screen coordinates, you can use TChartSeries.CalcXPos and TChartSeries.CalcYPos method. Example:

Code: Select all

var x0,y0: Integer;
begin
  x0 := Series2.CalcXPos(Index);
  y0 := Series2.CalcYPos(Index);
end;

This works fine for line, bar and point series. If series has more than two chart value lists (x,high, low, open ... values), a bit more complex code is needed. In the example below arrows will be drawn above every visible candle:

Code: Select all

// using tChart OnAfterDraw event !
procedure TForm1.Chart1AfterDraw(Sender: TObject);
var i: Integer;
  FromPoint,ToPoint: TPoint;
begin
  Chart1.Canvas.ClipRectangle(Chart1.ChartRect);

  With Series1 do // Series1 is TCandleSeries
    for i := FirstValueIndex to LastValueIndex do
    begin
      ToPoint.X := CalcXPos(i);
      ToPoint.Y := CalcYPosValue(HighValues.Value[i]);
      FromPoint.X := ToPoint.X;
      FromPoint.Y := ToPoint.Y - 20;
      ParentChart.Canvas.Arrow(True,FromPoint,ToPoint,7,7,MiddleZ);
    end;

  Chart1.Canvas.UnClipRectangle;
end;

for all other non-intersecting points are not visible

No simple way to do it. Calculate all intersection points and then draw arrow for individual intersection.

Posted: **Thu Apr 28, 2005 3:59 pm**

Marjan,

Thanks a lot, will try it out and confirm to you.

Satish

Posted: **Fri Apr 29, 2005 2:51 am**

Marjan,

Using the canvas method how do I color the arrow - I need to color it either red or green ? Also is there a way to fill the Arrow Series with transparent arrows - Actually I would be using 8-10 red/green arrows in a series having over 250 points.

Satish

Posted: **Fri Apr 29, 2005 3:27 pm**

Hi, Satish.

how do I color the arrow

This can be done by adding the following lines to chart OnAfterDraw event:

Code: Select all

  ...
  ParentChart.Canvas.Brush.Color := clRed;
  ParentChart.Canvas.Brush.Style := bsSolid;
  ParentChart.Canvas.Arrow(True,FromPoint,ToPoint,7,7,MiddleZ); 
  ..

Also is there a way to fill the Arrow Series with transparent arrows

Try setting arrow point color to clNone. But if you plan to use arrow series, there is a lot simpler solution : clear and repopulate arrow series when your data changes. Of course, you don't simply copy all points from original series, you only copy intersection points.

Steema Central

FInding x0,y0,x1,y1 for ArrowHead Series

FInding x0,y0,x1,y1 for ArrowHead Series