First of all, for a reasonable gWorld demo application, look over on the 
FB webring site(s); I'd suggest <http://www.stiinc.com/FB/>, and click on 
"sample source". There are several there - mine is under "Flying Brain 
Screensaver source", and you'll need (thanks to copyright restrictions) 
to download the freeware compiled app "FlyBrain" and steal the PICT 
resources...

My answers below come from that code - which is overkill for what you 
need, as it does double-buffered animation, but hopefully it'll help! 
(I've tried to remove the extraneous stuff from this posting, but I don't 
guarantee I got it all.)

>My hopes for a first-try success at using GWorlds in my PG project have 
>been dashed. I'm stuck. I'm sure, though, that one (or 20) of you can 
>tell me what I'm missing.
>
>1. I create a PICTURE using:

No problem here.

>2. I create a ColorGWorld with
>
>  gWorld& = FN buildGWorld(gwRect)  'FN from GRFX.FLTR

No problem here, as the relevant code is
  QDErr =  FN NEWGWORLD(theWorld&,0,#@t,0,0,0)
which gives a nice "default" gWorld of the size you specify.

>gwRect has the same Top & Bottom as the area into which I want to copy 
>it. The width is 3 times the width of the target area, the center third 
>having the same rect as the target. This means the Left coordinate is 
>negative. Could this be a problem? When I check the CGrafPort record, it 
>shows the coordinates as #0 #0 #(height) #(width). I'm not sure how (or 
>if) that affects the following...

Hm. Strange... all windows & gWorlds use "local" coordinates, which mean 
the upper-left is at 0,0. I'm not sure what you're getting by using 
non-zero values on the input.

I'd suggest using
  CALL OFFSETRECT(gwRect,-gwRect.left%,-gwRect.top%)
before the call. Then when you "copy back", you'll just need to offset by 
+1x, +2x, or +3x rather than -1x,0,+1x.

>3. I draw the gGridPict& into the GWorld& with:
>
>LOCAL FN calDrawGrid
>  DIM oldWorld&,oldDevice&
>  CALL GETGWORLD(oldWorld&,oldDevice&)    'get curr port
>  CALL SETGWORLD(gWorldH&,oldDevice&)     'change to GWorld&
>  PICTURE (gwL,gwT)-(gwR,gwB),gGridPict&  'coords from GWorld creation 
>  CALL SETGWORLD(oldWorld&,oldDevice&)'   'reset port
>END FN

Problem here. Try this; note the 0 on the SETGWORLD
   gOffDev& = FN GETGWORLDDEVICE(gWorldH&)
   CALL SETGWORLD(gWorldH&,0)                 'set output to offscreen 
port
   locked% = FN LOCKPIXELS(FN GETGWORLDPIXMAP(gWorldH&))
   LONG IF locked%
     CALL DRAWPICTURE(gGridPict&,gwRect)        
     CALL UNLOCKPIXELS(FN GETGWORLDPIXMAP(gWorldH&))
   END IF
   CALL SETGWORLD(oldWorld&,oldDevice&)          'set output back to 
window

>I can find no way of testing whether this FN does what I intend or not! 
>When I use MacsBug to look at oldWorld& as a CGrafPort, everything seems 
>okay, except the baseAddr comes up as a "bad pointer." I have no clue 
>what that tells me.

Me either! :-)

>4. I copy the central third of the GWorld to my window:
>
>LOCAL FN calCopyWeek
>  DIM wPtr&
>  GET WINDOW gOutputWnd, wPtr&
>  FN copyBits(gWorldH&,wPtr&,gCalRect,gCalRect,_srcCopy)
>END FN
>
>Here gCalRect is the rect of my target object, which should correspond to 
>the center third of the GWorld. Even if I am mistaken about the rects 
>being the same, it seems I should see at least a piece of the picture I 
>drew to the (entire) GWorld, no?

I'd be concerned about gCalRect; you might try creating a new rect, say 
gSourceRect, from 0,0 to the height & width needed; that should give you 
the "left third" of your gWorld, which is fine for testing;

   CALL GETGWORLD(oldWorld&,oldDevice&)    'get curr port (not GET WINDOW)
   locked% = FN LOCKPIXELS(FN GETGWORLDPIXMAP(oldWorld&))
   LONG IF locked%
     locked2% = FN LOCKPIXELS(FN GETGWORLDPIXMAP(gWorldH&))
     LONG IF locked2%
       CALL 
COPYBITS(#gWorldH&+2,#oldWorld&+2,gSourceRect,gCalRect,_srcCopy,0)
       CALL UNLOCKPIXELS(FN GETGWORLDPIXMAP(gWorldH&))
     END IF
     CALL UNLOCKPIXELS(FN GETGWORLDPIXMAP(oldWorld&))
   END IF

>I do get a bitcopy to the screen, but it contains lovely green noise 
>rather than the gGridPict& I drew to the GWorld.

That tells me your offsets are wrong; note the "#gWorldH&+2" in the above!

>I see there is a command to LOCKPIXELS which I haven't used. Can someone 
>tell me what it does; when and why it is necessary? This can't be my 
>problem, can it?

Not likely - it's "insurance" against the Memory Manager moving your 
memory around on you in the middle of your CopyBits. For a simple 
application, you can leave it out during development - just be sure to 
put it in before you ship to avoid weird untraceable bug reports later!

>Let me know if I've not supplied enough info. Any help will be greatly 
>appreciated.

Plenty of info. Very well done question, with just the right amount of 
code!

Bill