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Multi-rect Sprite Constraint

March 7, 1999
by Pat McClellan

Dear Multimedia Handyman,

Can I make a sprite constrained within more than one sprite?

Dana Benson

Dear Dana,

Nice direct question. So let's get right to the answer. No.

Download Mac or PC

At least, not using Director's built-in constraint of sprite Lingo. However, we can fake it pretty easily with a behavior. We'll call it a multi-rect contstraint behavior. Let's make it so that the author can specify 2 sprites, within which our movable sprite will be constrained. So, our properties will include pSpriteA and pSpriteB; a pFlag property which will be set to either #move when the sprite is being dragged, or #stop; plus pRectA and pRectB, properties to store the rects of pSpriteA and pSpriteB. (And, of course, a property to hold the moving sprite's spriteNum.)

The author will specify pSpriteA and pSpriteB when the behavior is dropped on the sprite. All the other properties are assigned automatically in the beginSprite handler. The mouseDown and mouseUp handlers simply change the state of pFlag (from #stop to #move and back.)

The real action happens on the exitFrame handler. In this handler, we're going to set a variable (mouseLoc) to point(the mouseH, the mouseV). Then -- assuming pFlag is set to #move -- we'll check to see if mouseLoc is within either of the specified rects. If it is inside either one, then we'll set the loc of the moving sprite to mouseLoc. If the mouse wanders outside the given rects, then the position of the moving sprite is not updated.

Here's the code.

-- Multirect Constraint
-- copyright © 1999, ZZP Online, LLC
property pSpriteA, pSpriteB, pRectA, pRectB, pFlag, pMySprite
on getPropertyDescriptionList me
  set pdlist to [:]
  addprop pdlist, #pSpriteA, [#comment:"First Constraining ¬
    Sprite", #format:#integer, #default:1]
  addprop pdlist, #pSpriteB, [#comment:"Second Constraining ¬
    Sprite", #format:#integer, #default:2]
  return pdlist
end getPropertyDescriptionList
on beginSprite me
  set pRectA = the rect of sprite pSpriteA
  set pRectB = the rect of sprite pSpriteB
  set pMySprite = the spriteNum of me
  set pFlag = #stop
on mouseDown me
  set pFlag = #move
on mouseUp me
  set pFlag = #stop
on mouseUpOutside me
  set pFlag = #stop  
end mouseUpOutside
on exitFrame me
  set mouseLoc = point(the mouseH, the mouseV)
  if pFlag = #move then
    if inside(mouseLoc, pRectA) or inside(mouseLoc,pRectB) then
      set the loc of sprite pMySprite = mouseLoc
    end if
  end if

If you want to have more than 2 sprites, it's a simple matter to add more sprites/rects to the behavior. Good luck with your program.

Patrick McClellan is Director Online's co-founder. Pat is Vice President, Managing Director for Jack Morton Worldwide, a global experiential marketing company. He is responsible for the San Francisco office, which helps major technology clients to develop marketing communications programs to reach enterprise and consumer audiences.

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