Path: utzoo!attcan!uunet!mcvax!kth!draken!jakob
From: jakob@nada.kth.se (Jakob Cederlund)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Smoothly dragging small pictures
Summary: OffScreen BitMaps, worth the price?
Keywords: drag smooth copybits offscreen
Message-ID: <1041@draken.nada.kth.se>
Date: 16 May 89 08:04:51 GMT
References: <12492910881010@osu-20.ircc.ohio-state.edu> <1065@umn-d-ub.D.UMN.EDU> <1488@murtoa.cs.mu.oz.au> <1068@umn-d-ub.D.UMN.EDU>
Reply-To: jakob@nada.kth.se (Jakob Cederlund)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 16

I've done dragging routines in C.  First, I used an offscreen
bitmap containing the "background" for the object and a bitmap
twice the size of the object for drawing the new object.  With
those two bitmaps, the dragging loop needed to do three CopyBits
for each increment of the drag.

However the big, "background" bitmap became too big when dragging
between windows. On my Mac II-system at work, with a large monitor and
a colour ditto, this bitmap would take up 1.5 meg. So I dumped the
background bitmap and used a method which needed five blit's per
drag-step.

I can mail a description of the method (and source if I can dig
it up) if anyone is interested.

/Jakob Cederlund, Royal Institute of Technology Stockholm Sweden
jakob@nada.kth.se