Scaling Objects while Dragging

Date:    Fri, 1 Jul 1994 12:19:30 -0500
From:    Matthew Caldwell <sexkittn@BURN.DEMON.CO.UK>
Subject: Re: Speed and Mac 4.0

>I am trying to do a drag and drop operation that rescales as it drags,
>ie. in some kind of 3d perspective

Well, here's a modified version of something I used for a similar effect. Note that it isn't friendly to other things going on at the same time -- it loops inside the handler while the mouse is still down. (QT movies will continue to play, though). There are various other ways in which it isn't exemplary scripting practice too, but anyway...

A constraining sprite is used to set the area in which the dragging can occur, and the amount of scaling is calculated relative to *vertical* movement within it, but it shouldn't be too difficult to change it for horizontal movement if desired, or even separate scaling in each dimension.

In this case the scaling is:

   start position = bottom of constraint box = 100%
   top of constraint box = 45%

This works very smoothly and nicely when the sprite is a quickdraw shape, rather more jerkily when it is a large & complex bitmap.

The handler goes in the cast script of the thing being moved. The globals need to be set beforehand, or alternatively you could pass both sprites as parameters and calculate the other things at the top of the handler (probably a better idea all round, actually):

on mouseDown
  -- baseTop is the top of the constraining sprite
  -- baseRange is the height of the constraining sprite
  -- baseWidth & baseHeight are the starting width & height of the
  -- dragged (scaling) sprite in channel whichSprite
  global baseTop, baseRange, baseWidth, baseHeight, whichSprite


  if the puppet of sprite whichSprite = false then puppetSprite whichSprite, true

  set relativeV to the locV of sprite whichSprite - the mouseV
  set relativeH to the locH of sprite whichSprite - the mouseH

  repeat while the stillDown
    -- move the figure
    set the locV of sprite whichSprite to relativeV + the mouseV
    set the locH of sprite whichSprite to relativeH + the mouseH
    -- scale it for pseudo-perspective
    set scaleFactor to (((the locV of sprite whichSprite) - baseTop) * 0.55 / baseRange) + 0.45
    set the width of sprite whichSprite to baseWidth * scaleFactor
    set the height of sprite whichSprite to baseHeight * scaleFactor
    -- show it
    updateStage
  end repeat
end mouseDown