Direct drawing on Form canvas (TCanvas) from custom method
lazarus / 39-Graphics

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whips · 2014-01-14 10:53

Hi all,
I am verry sorry but I have to ask again

I finished small unit with 2 methods
Code: [Select]
unit vector;
{$mode objfpc}{$H+ $M+}
interface
 uses
  Classes, SysUtils,Graphics;
type
     
type

  { TForm1 }
  {$M+}
  Tlcd7 = class(TComponent)


  private
     { private declarations }
     upper,leftupper {... etc cut-off.. }: array[0..8] of Tpoint;

  public
     { public declarations }
     procedure initvectors; //initialize values
     procedure drawobject(canv : Tcanvas);

  end;   


And I wish to use this unit this way

Code: [Select] TForm1 = class(TForm)
    CheckBox1: TCheckBox;
     lcd : Tlcd7;


and somewhere in event handler wan't to use this way.
Quote// onChange for example
begin
  lcd.initvectors();
  .... { zoom vectors, or else move, rotate, etc.... }
  ....
lcd.drawobject(need to pass parrent/form canvas);
  ....
end;



Quoteprocedure Tlcd7.draw7lcdsegment(canv : Tcanvas);

begin
   canv.Brush.color:= clwhite;
   //drawtest(upper);
   canv.Polygon(upper,true,1,8);
   canv.Polygon(leftup,true,1,8);
   canv.Polygon(middle,true,1,7);
   canv.Polygon(rightup,true,1,7);
   canv.Polygon(rightdown,true,1,7);
   canv.Polygon(botton,true,1,7);
   canv.Polygon(leftdown,true,1,7);
end;   



How to do it right way
I don't want create custom widget only simply
drawing on canvas and have small unit for next aplication in future.

I have no experience with creating custom elements and it's over my
skill make it now.

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taazz · 2014-01-14 11:02

use forms onPaintEvent for your code. eg
Code: [Select]procedure TMainForm.FormPaint(Sender : TObject);
begin
  lcd.initvectors();
  .... { zoom vectors, or else move, rotate, etc.... }
  ....
  lcd.drawobject(Self.Canvas);   
end;

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whips · 2014-01-14 12:21

Thank to Taaz
I forgot call constructor before working with class.
That's produce runtime error with (SIGSEG)

Code: [Select]procedure TForm1.FormCreate(Sender: TObject);
begin
  lcd := Tlcd7.Create(self);
end;