Panning the stage (fast!)

Date:    Tue, 21 Apr 1998 15:38:15 -0700
From:    "Terry R. Schussler" 
Subject: Panning the stage, fast.

>I know it's not exactly ground-breaking (in fact, something much like it
>can be seen on the 1996 ID Magazine CD-ROM), but I'm trying to create an
>interface wherein a user can navigate a space much larger than the confines
>of the screen.  For example, rolling the mouse towards the top of the
>screen would cause their view to pan upwards, revealing elements up there.
>As they roll left, the scene pans left, and so on.

You asked a good question which caused me to do some thinking. Based on some recent work, I've crafted a handler which will address part of your question - rapid panning of the stage. Rather than changing the positions of several sprites one at a time, I've approached the problem from the perspective of changing your "viewport" of the stage using the oft overlooked "drawRect of windowObject" property. You could easily adapt a version of this code to algorithmically change the coordinates of the drawRect using math as well. (i.e. set the drawRect of the stage = the drawRect of the stage + rect(-10,0,-10,0) would set the stage to shift left 10 pixels.)


-- PLACE THESE SCRIPTS IN A MOVIE SCRIPT MEMBER
on mouseDown
  dragStage
end mouseDown

-- This handler will change the drawRect of the stage
-- of whichever window is active at the time it is called
-- written by Terry R. Schussler, g/matter, inc.
-- version 1.0
-- 4/21/98
--
on dragStage
  -- grab the original mouse coordinates
  put the mouseH into Horiginal
  put the mouseV into Voriginal
  -- grab the original drawRect coordinates
  put the drawrect of the activeWindow into originalDrawRect
  -- make a copy of the original drawRect
  -- NOTE: rects *are* property lists and
  -- must be dereferenced to make a true copy
  set newDrawRect = duplicate(originalDrawRect)
  repeat while the stillDown
    set Hoffset = the mouseH - Horiginal
    set Voffset = the mouseV - Voriginal
    -- NOTE: Use of case is faster than an IF test
    -- An IF test would require checking both variables regardless
    -- of whether or not Hoffset was non-zero
    case FALSE of
      Hoffset, Voffset : -- redraw the window only if necessary
        nothing
      otherwise
        --    if abs(Hoffset) > 1 OR abs(Voffset) > 1 then
        set the left of newDrawRect = the left of newDrawRect + Hoffset
        set the right of newDrawRect = the right of newDrawRect + Hoffset
        set the top of newDrawRect = the top of newDrawRect + Voffset
        set the bottom of newDrawRect = the bottom of newDrawRect + Voffset
        set the drawrect of the activeWindow to newDrawRect
    end case
  end repeat
  -- use the next line to snap the drawRect back to the rect
  -- that was active when this handler was started
  set the drawrect of the activeWindow = originalDrawRect
  -- use the next line to snap the drawRect back to the rect
  -- that was defined as the original stage
  --  set the drawrect of the activeWindow = the rect of the activeWindow +
rect(-the left of the rect of the activeWindow, -the top of the rect of the
activeWindow, -the left of the rect of the activeWindow, -the top of the
rect of the activeWindow)
end dragStage