how to color a single point of a lineseries
lazarus / 55-TAChart

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frederic · 2017-12-19 16:30

dear specialists

i have a lineseries  with  showpoints:=true
all these points  have the color defined by pointer.brush

i want to change the color of one point of the series differently by
code
is that possible ?

fredreic

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wp · 2017-12-19 16:45

When you add a point to the series by calling the Series' Add or AddXY
you can specify its color as a parameter:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
Add(AValue: Double; AXLabel: String = ''; AColor: TColor = clTAColor):
Integer; function AddXY(AX, AY: Double; AXLabel: String = ''; AColor:
TColor = clTAColor): Integer; inline;function AddXY(AX, AY: Double;
const AYList: array of Double;  AXLabel: String = ''; AColor: TColor =
clTAColor): Integer;  e.g. procedure TForm1.FormCreate(Sender:
TObject);begin  Chart1LineSeries1.AddXY(0, 10); 
Chart1LineSeries1.AddXY(1, 12);  Chart1LineSeries1.AddXY(2, 11, '',
clRed);   // <-- this one will be red  Chart1LineSeries1.AddXY(3,
10);end; 
If you add points to a TListChartSource the calls are similar
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i function
Add(AX, AY: Double; const ALabel: String = ''; AColor: TChartColor =
clTAColor): Integer;function AddXYList(AX: Double; const AY: array of
Double; const ALabel: String = ''; AColor: TChartColor = clTAColor):
Integer;
If you pass the points via a UserDefinedChartSource then you specify
the color in the parameter AItem:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.UserDefinedChartSource1GetChartDataItem(  ASource:
TUserDefinedChartSource; AIndex: Integer; var AItem:
TChartDataItem);begin  AItem.X := <some x>;  AItem.Y := <some y>;  if
AIndex = 2 then AItem.Color := clRed;      // Force point with index 2
to be red.end;

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frederic · 2017-12-19 20:30

thanks wp,

so ,when i start with
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.FormCreate(Sender: TObject);begin  Chart1LineSeries1.AddXY(0,
10);  Chart1LineSeries1.AddXY(1, 12);  Chart1LineSeries1.AddXY(2,
11);  Chart1LineSeries1.AddXY(3, 10);end;    //an change color by
buttonclickprocedure TForm1.Button1Click(Sender:
TObject);begin Chart1LineSeries1.AddXY(2, 11, '', clRed);   // <--
this one will be redend;   // and back procedure
TForm1.Button2Click(Sender: TObject);begin Chart1LineSeries1.AddXY(2,
11);  // back to the original color settingend;                      
             
that's simple; only overwriting

i hope this is also valid when drag  this specific point;
we are going to test it

frederic

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wp · 2017-12-19 21:19

Hmmm..., looks strange. In FormCreate you add a point at x=2, y=11 in
normal color. In Button1Click you add another point at the same
location in red color, and in Button2Click you add another one, now in
normal color again. In the end you'll have multiple points at the same
location. I guess this is not what you want.

In order to colorize an already existing point you should use the
method SetColor which is available for most series; it gets the point
index and the new color as parameters. If the new color is clDefault
(or clTAColor) then the color is restored to the series color.

See attached demo.

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frederic · 2017-12-20 08:44

wp,
yes, i misinterpreted your answer

addxy means :adding a new point(although it has the same xyvalues
),and not replace
this explains much of the troubles i got.

so dragging is also not a problem anymore because the pointindex is
the reference for color modifications of points

thanks for leading me out of the tunnel
frederic