Use of PaintBox

[Davidous]

Hello,

I would like to ask you of how to use a PaintBox on my Form.
I can draw on the Form Canvas, but now I would like to draw a line on the Paintbox.
Could someone please provide me with a short sample code?

[wp]

Not tested but it should give you the idea:

Code: Pascal  [Select][+][-]

1. procedure TForm1.PaintboxPaint(Sender: TObject);
2. begin
3.   with Paintbox1 do begin
4.     Canvas.Brush.Color := clWhite;
5.     Canvas.FillRect(0, 0, Width, Height);
6.     Canvas.Pen.Color := clRed;
7.     Canvas.Line(0, 0, Width, Height);
8.   end;
9. end;

[Davidous]

Thank you, but how to call it.
For the canvas of the form there is an OnPaint event, but there isn't such for the PaintBox.

[howardpc]

Thank you, but how to call it.
For the canvas of the form there is an OnPaint event, but there isn't such for the PaintBox.

Yes there is.

Why do you think otherwise?

[Davidous]

Oh yes, there is, sorry
But what I wanted to say, that I cannot type Paintbox.Paint for some reason. Why is that?
(For my form I can type Form.Paint and then the canvas is painted.)

[VTwin]

You don't normally call Paint, it is called as necessary when the form or control is redrawn. Use Update if required to force it for some reason, or Invalidate:

https://stackoverflow.com/questions/1251009/whats-the-difference-between-refresh-update-and-repaint

[lucamar]

Oh yes, there is, sorry
But what I wanted to say, that I cannot type Paintbox.Paint for some reason. Why is that?
(For my form I can type Form.Paint and then the canvas is painted.)

Paint is a protected method in both classes. You can call it for the form because you're dealing with a derived class (MyForm = class(TForm)).

However, all the default Paint method does is call the OnPaint event if set, so you may as well call it directly; i.e. instead of calling

Code: [Select]

MyPaintBox.Paintinvoke the handler directly as, for example:

Code: [Select]

MyPaintBoxPaint(Self)(whatever it is called in your program, of course).

[Davidous]

Thank you.
Sadly I cannot get it to work. I don't know why...

[Davidous]

I just created a whole new form and placed a paintbox on it. Now it works
Thank you for all the ideas!

[lucamar]

I just created a whole new form and placed a paintbox on it. Now it works
Thank you for all the ideas!

How were you doing it before? Just curiousity.

[Davidous]

I have a very long procedure and a form. On this form I have many graphs.
It is still interesting, because if I place a PaintBox on this Form, then for some reason I cannot draw the line I want. If I give a PaintBox to an other (empty) form, then it works. So I still don't understand...

Right now I work with these 2 lines:

PaintBox1.Canvas.Pen.Color:=clBlack;  PaintBox1.Canvas.Line(PaintBox1.Left+20,PaintBox1.Top+PaintBox1.Height,PaintBox1.Left+20,PaintBox1.Top);

On 1 form it doesn't work, on the other it does...

[lucamar]

And you're doing that in the PaintBox's OnPaint handler? Strange; it should work the same wherever it is.

[Davidous]

Yes