OpenEuphoria

RE: win32lib scrollbar bugs (For library developers)

• Posted by Al Getz <Xaxo at aol.com> Feb 03, 2003
• 451 views

daryl_vdb at hotmail.com wrote:
> to Derek Parnell (and others)
> 
> Win32lib seems to have a problem with scrollbars that have long
> ranges.  I have included a small test program which exposes this
> bug.  When the scroll range is set to anything over 65535, win32lib
> won't let you use the whole scrollbar.  Try this for yourself to
> see what I mean.  You can still use the arrows to scroll past
> 65535, but if you drag the scrollbar and watch the number under it,
> you'll notice that they skip back to 0.
> 
> Scrollbars built into windows are even worse.  They limit you to
> 100, which is really rediculous and makes these scrollbars
> virtually useless.
> 
> regards,
> Daryl Van Den Brink
> 
> 
My guess is that win32lib just needs a 32 bit scrollbar update 

There certainly is a way to scroll 32 bit in windows 95 and up, but 
there is 
a minor bug in some versions of windows which prevents doing things 
exactly
the way the official documentation might lead you to believe.

First off, forget about:

SetScrollPos, SetScrollRange, GetScrollPos, and GetScrollRange.
Basically, forget they exist 

The two functions to use are:
1. GetScrollInfo()
2. SetScrollInfo()

These two functions provide the 32 bit interface for windows scrollbars.
If you try to use any other functions, something wont work the way you
expect it to.

There is a bug in some windows versions so you MUST use SIF_ALL
with the SCROLLINFO struct.  Any other value might cause the
nTrackPos member to become invalid.

For reference when programming in Euphoria:
SIF_ALL = (SIF_RANGE | SIF_PAGE | SIF_POS | SIF_TRACKPOS)
where
SIF_PAGE          =  0x0002
SIF_POS           =  0x0004
SIF_RANGE         =  0x0001
SIF_TRACKPOS      =  0x0010

You will process:

iMsg = WM_VSCROLL or iMsg = WM_HSCROLL

If i remember right, I dont think nPos is valid when the user drags
the thumb, but nTrackPos is.

In any case, you dont want to use any other functions because they wont
support the case when the user drags the thumb (32bit).

My editor uses this technique and has been tested with hundreds of 
thousands
of lines of text and way over 100MB of text.  The scrolling is per line,
not per pixel, but more then 65536 lines of text will still require the 
use of
the 32 bit scrolling technique.


Good luck with your programming,
Al