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

[Rolf-Werner Eilert]

Am 09.01.2012 12:51, schrieb 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,
>

Ok, I think I understand: With the help of ScrollX and ScrollY I have to 
decide at which coordinate within my large drawing I start to draw to 
1,1 on the DrawingArea?

Rolf