[Lazarus] TAChart with transparent background

[Roberto P.]

Though really late, I can confirm that the solution is working fine.
I still have to add some profiling code to measure it, though with added
background it seems perceivably slower even on a recent PC (core i5 vpro).
Are BGRA or other backends known to be faster?

thanks anyway for the help!

R#

2014-09-04 1:08 GMT+02:00 Roberto P. <padovani.r at gmail.com>:

> Thank  you very much.
> I need a background image, therefore as soon as I am back at the office
> I'll try your code.
> Thank you again!
>
> R#
>
>
> 2014-09-02 18:18 GMT+02:00 Werner Pamler <werner.pamler at freenet.de>:
>
>> It is not fully clear to me what you mean by "a chart with transparent
>> background". Do you want to see the form underneath the chart? I fear this
>> is not easily possible. Or do you want to have a background image in the
>> chart? For the latter case this code is working fine with me:
>>
>> type
>>   TForm1 = class(TForm)
>>     Chart1: TChart;
>>     procedure Chart1BeforeDrawBackground(ASender: TChart; ACanvas:
>> TCanvas;
>>       const ARect: TRect; var ADoDefaultDrawing: Boolean);
>>     procedure Chart1BeforeDrawBackWall(ASender: TChart; ACanvas: TCanvas;
>>       const ARect: TRect; var ADoDefaultDrawing: Boolean);
>>     procedure FormCreate(Sender: TObject);
>>     procedure FormDestroy(Sender: TObject);
>>   private
>>     { private declarations }
>>     FBackImage: TPicture;
>>   public
>>     { public declarations }
>>   end;
>> ....
>> procedure TForm1.Chart1BeforeDrawBackWall(ASender: TChart; ACanvas:
>> TCanvas;
>>   const ARect: TRect; var ADoDefaultDrawing: Boolean);
>> begin
>>   ADoDefaultDrawing := false;
>>   ACanvas.StretchDraw(ARect, FBackImage.Graphic);
>> end;
>>
>> procedure TForm1.Chart1BeforeDrawBackground(ASender: TChart; ACanvas:
>> TCanvas;
>>   const ARect: TRect; var ADoDefaultDrawing: Boolean);
>> begin
>>   ACanvas.GradientFill(ARect, clSkyBlue, clWhite, gdVertical);
>>   ADoDefaultDrawing := false;
>> end;
>>
>> procedure TForm1.FormCreate(Sender: TObject);
>> begin
>>   FBackImage := TPicture.Create;
>>   FBackImage.LoadFromFile('C:\lazarus-svn\images\splash_logo.png');
>>   // please adapt this path to your lazarus installation
>> end;
>>
>> procedure TForm1.FormDestroy(Sender: TObject);
>> begin
>>   FBackImage.Free;
>> end;
>>
>> The basic idea is to assign a handler to the chart events
>> OnBeforeDrawBackWall or OnBeforeDrawBackground and disable the default
>> background painting by setting ADoDefaultDrawing to false. The first event
>> replaces painting of the area enclosed by the chart's frame ("Back wall"),
>> the other one replaces painting of the entire chart background. Above
>> example paints the Lazarus splash-logo as BackWall and a gradient as
>> background.
>>
>> Maybe I'll once write a tutorial on this topic...
>>
>>
>> --
>> _______________________________________________
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>> Lazarus at lists.lazarus.freepascal.org
>> http://lists.lazarus.freepascal.org/mailman/listinfo/lazarus
>>
>
>
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