Paintbox stretches in scroll box

WEB TMS WEB Core
1

I put a paintbox in a scrollbox, having the same size as the scrollbox. When I then draw in the paintbox and beyond the size of the scrollbox, To get the whole drawing, I have to adapt the paintbox size (width and/or height) at runtime, which is OK.

However, when setting back the paintbox size to the scrollbox size before starting a next drawing, no longer produces a complete drawing. Instead, it only draws the surface of the scrollbox and then stretches that up to the actual drawing surface.

So, once a paintbox becomes larger than a scrollbox, it is not possible to start with an original surface.

The example below is code for a scrollbox+paintbox+button.

Attached is the complete example with alternative tries:
PaintboxExample.zip (7.3 KB)

Is there a proper way to adapt the size of a paintbox?

Kind regards,

Michel Huybrechts
Micriconsult BV

procedure TForm1.WebFormShow(Sender: TObject);
begin
v_CanPaint1 := False;
end;

procedure TForm1.WebButton1Click(Sender: TObject);
begin
v_CanPaint1 := True;
WebPaintBox1Paint(WebPaintBox1)
end;

procedure TForm1.WebPaintBox1Paint(Sender: TObject);
{
Works correctly, but only the first time. The next paint stretches the
visible part up to the calculated height???
}
begin { TForm1.WebPaintBox1Paint }
if v_CanPaint1
then
begin
{ Reset the height }
WebPaintBox1.Height := WebScrollBox1.Height;
WebPaintBox1.Canvas.Clear;
WebPaintBox1.Canvas.MoveTo(0, 0);
WebPaintBox1.Canvas.LineTo(150, 150);
WebPaintBox1.Canvas.MoveTo(100, 1000);
WebPaintBox1.Canvas.LineTo(100, 100);
WebPaintBox1.Canvas.TextOut(30, 10, 'Visible text');
WebPaintBox1.Canvas.TextOut(30, 500, 'Invisible text');
{ Set the height: does not work the second time. Drawing is stretched }
WebPaintBox1.Height := 1000
end
end { TForm1.WebPaintBox1Paint };

2

It is not a good idea to change the size of a control during its painting.
Normally, a change of size would need to force a repaint and you risk to have an endless loop.
Instead here you see the canvas as-is just being scaled.

I recommend to move size changing out of painting code.

3

Dear Sir,

Indeed. This solves the problem and also prevents useless calls to the paint.

Thank you for this answer.

Kind regards,

Michel Huybrechts

Micriconsult BV

www.micriconsult.be