Path: utzoo!utgpu!watmath!att!ucbvax!tut.cis.ohio-state.edu!cs.utexas.edu!utastro!james
From: james@utastro.UUCP (James McCartney)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Joe's bug list for the THINK Class Library, vol. 1
Summary: continuous thumb scrolling
Message-ID: <4283@utastro.UUCP>
Date: 30 Aug 89 22:31:54 GMT
References: <3812@ncsuvx.ncsu.edu>
Organization: U. Texas, Astronomy, Austin, TX
Lines: 55

In article <3812@ncsuvx.ncsu.edu>, jnh@ecemwl.ncsu.edu (Joseph N. Hall) writes:
> 
> 2.  It would be nice to have a scroll bar that implemented the equivalent
>     of a TrackControl function for the thumb, so that the "live" thumb
>     dragging available on the NeXT, etc., could be implemented.
> 
    I did this in my own object library :

HThumbScroll(this, cntl, where)
	hFrame this;
	ControlHandle cntl;
	Point where;
{
	int pix;
	int value;
	long valrng, pixrng, vdown;
	Point mdown, mse;
	Box limits;
	
/* normal way to do a thumb :
		TrackControl(cntl, where, NIL);
		value = GetCtlValue(cntl);
		Send(this, mPutOrigin, value, This.origin.v, true);
*/

/* fancy a la NeXT way : */

	valrng = GetCtlMax(cntl) - GetCtlMin(cntl);
	pixrng = (**cntl).contrlRect.right - (**cntl).contrlRect.left - 48;
	mdown = where;
	vdown = GetCtlValue(cntl);
	limits = This.fbox;
	while(StillDown()) {
		FocusParent(this);
		GetMouse(&mse);
		pix = mse.h - mdown.h;
		/* calc control value : */
		value = vdown + pix * valrng / pixrng ;
		/* move origin of frame, scrollrect contents */
		Send(this, mPutOrigin, value, This.origin.v, false);
		/* keep track of update region */
		HLock(this);
		SectRect(&limits, &This.fbox, &limits);
		HUnlock(this);
	}
	Focus(this);
	UpdateHandLimits(this, &limits);
}

   Some of the above is probably not intelligible without seeing the
rest of the code. but you get the general idea.
   I spent about 10 minutes looking at how to do it in the THINK class
library before moving on to other things.

--- James McCartney