[Gambas-user] Gambas3: ScrollArea doesn't scroll

[Benoît Minisini]

Le 09/01/2012 09:08, Rolf-Werner Eilert a écrit :
> Here I am definitely understanding something wrong.
>
> I need a graphical object that allows for drawing some sort of
> specialized table that can expand and collapse certain rows like a
> TreeView. So I decided to program that either based on HTML in a
> RichText thing or better everything by myself in a DrawingArea. The
> DrawingArea would have to expand according to the contents and be
> controlled by ScrollBars. Then I found there is a ScrollArea in Gambas3
> which could do 90 % of the job by itself.
>
> This is my understanding: A ScrollArea should be a DrawingArea which is
> enlarged automagically as soon as you draw beyond its borders and will
> produce ScrollBars for the user to slide the area forth and back below
> the visible frame that confines it on screen.
>
> Do you agree?
>
> Ok, I have a small ScrollArea, say 100 x 100 px.
>
> In Form_Open, I set its Contents to 2500 x 2500 px as from the
> documentation I understand it won't do that by itself (why not?).
>
> It shows two ScrollBars.
>
> I draw a line from 1,1 to 500,500.
>
> When I move the ScrollBars, nothing happens, i. e. the image shows the
> beginning of the line and stands still. This happens in qt (KDE4) as
> well as GTK (LXDE).
>
> The ScrollArea is not cached. I guess if I really have to move it by
> code, I will produce a whole lot of unnecessary Draw events.
>
> But just in case, how would their position be calculated? I would have
> to read the ScrollBar values, but their output is not documented - is it
> percent? Or relative to anything?
>
> (I cannot give you code snippets as this happened on my laptop this
> weekend, and I don't have G3 here in my office yet.)
>
> Really looking forward to your comments!
>
> Rolf
>

Because when you draw, you need to use the ScrollX and ScrollY to know 
how much you must translate what you draw inside the Draw event handler.

Nothing is physically moved, it is really "just" a DrawingArea with two 
scrollbars entirely made in Gambas (the source code is in gb.form if you 
are curious).

Regards,

-- 
Benoît Minisini