Path: utzoo!mnetor!uunet!oddjob!hao!ames!eos!aurora!labrea!decwrl!decvax!dartvax!eleazar!obie
From: obie@eleazar.Dartmouth.EDU (Timothy D. Notestein)
Newsgroups: comp.sys.amiga
Subject: Bobs and Double Buffering
Message-ID: <8259@eleazar.Dartmouth.EDU>
Date: 25 Feb 88 17:05:32 GMT
Reply-To: obie@eleazar.Dartmouth.EDU (Timothy D. Notestein)
Followup-To: comp.sys.amiga
Distribution: comp.sys.amiga
Organization: Dartmouth College, Hanover, NH
Lines: 70
Keywords: bobs, graphics, animation, buffering
Summary: How do I get DBuffer to work?


[ is there really a line eater?  only in isolated galaxies.... ]
 
On page 149 of the RKM Libraries and Device Manual, we are informed
that it is indeed possible to have double-buffered blitter objects.
 
I have not, as of yet, seen any source code that is using this precise
feature.  Now, I have seen nifty display hacks that use double 
buffering as an aspect of the viewport.
 
However, this is not good for me, as intuition in general doesn't take
well to double buffering, and I really do need the intuition environment
existing peacefully as well.  Basically, I'm writing an application that
requires that the user be able to drag icons around on the screen.  Currently,
the icons are so large (1/8th of screen apiece) that the irritating flicker
is ever-present whenever dragging the icons.

Without attempting double-buffering on the part of the bobs, everything
is functioning properly, w/ exception of the flicker.  If I allocate
DBufPacket for my bob, preset BufY, BufX coordinates (this shoudn't (?)
make any difference; set BufPath to NULL; set BufBuffer to an allocated
array the same size as my previous SAVEBACK array.
 
  struct DBufPacket my_icon_dbuf[number_of_icons] = 
  {
    0,0,    /* BufY, BufX */
    0,      /* BufPath    */
    &drawingDB[0]   /* BufBuffer */
 },
 ....
 
When declaring my actual bob...icon/images
 
struct MyIcon {struct Bob, Gadget} my_icon[number_of_icons]
  { 
   {
    0,
    &faceSave[0],
    &faceMask[0],
    NULL,NULL,
    &faceVS,  /* virtual sprite */
    NULL,
    &my_icon_dbuf[0],
    0
   },
  ...

This is all that the RKM says is necessary for bob double-buffering.
 
Is there something that I'm missing?  Do i HAVE to have the Rastport set up
for double-buffering, or anything like that?  Do I have to add the bob twice?
(I notice that it's documented that if double-buffering, you may have to
 remove it twice, but it doesn't mention AddBob())
 
Is there some maintainence that has to be done by my program everytime I
move a bob or something?
 
Symptoms:  The display comes up okay, but when I drag an icon around,
it's leaving bits and pieces of itself behind.  As well, if part of one
icon passes under another  (sorry, when I say icon, I DO mean bob), then
I get a kind of double-flickering affect, kind of.. (NOW YOU SEE IT, NOW
YOU DON'T).  But, I also don't notice any movements being at ALL smoother.
 
Anyone have any ideas/suggestions?  Also, if anyone has public domain source 
code that accomplishes something along these same lines, I WOULD GREAT
appreciate it if you could forward it, so I can get a grasp on what I'm
doing wrong.

Thanks in advance,
Tim