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Vector Shape Morphing

May 24, 1999
by Pat McClellan

Dear Multimedia Handyman,

Well, I'm a French designer, I'm not a programmer, but I like to play with lingo and search for new graphical solutions. I started to watch the new shapes in director 7. I think it's a great thing. I started trying to morphe a shape to another one (ex: a star to a heart) and it works. Then I wanted a behavior for progressive morphing. Now, the problem is that I'm not able to tell the morphing member "stop your morph, you're the good form". Can you help?


Credit: Sebastiano sent the code from his unsucessful attempt at the behavior, much of which I have used in this answer. I have used the French terms he did.

Dear Sebastiano,

Nice job on your attempt. You've grasped the basic idea but just need some refinement. I'll recap the process required for morphing one vector shape into another. (For a complete explanation of vector members, read Will Turnage's great article on vector shapes.)

We know that each vector shape is a drawn by connecting lines between points on a list, which is called the vertexList. Since this is a list in the standard sense of Lingo, there are some quick operations we can do to an entire list. For example...

set listA = [5,10,15]
set listB = [2,3,4]
put listA - listB
-- [3, 7, 11]

In this example, when we subtract listB from list A, the result is a new list where the first item is the difference between the first item of listA and the first item of listB. This is a very handy capability.

Now, assume that we have two vertexLists, each with the same number of points (that's very important). If we subtract one list from the other, we'll get a list of points which represents the difference between each corresponding point in the two lists. That list is precisely the amount and direction we would have to move each vertex in order to change the first shape to the second one.

Now, since we want to make that change over a number of frames, we need to figure out the incremental change for each vertex per frame. So, if we take the list representing the whole change and divide it by the number of frames in our morph animation, we'll get a list of the incremental change (per frame) for each vertex.

Download a sample movie in Mac or PC format

So that's the concept. Now let's get to the Lingo. We'll start with the getPropertyDescriptionList handler. This will let the author specify values for the initial shape, the target shape, and the number of frames. Note that the vector member on stage should be a different cast member from either the start or end shape of your morph. That's important because the morph will permanently alter your morphing vector cast member (not just the sprite instance.) So, unless you want to recreate your initial shape again and again, make a copy of it and specify that copy as your starting shape.

-- VectorMorph Behavior
-- copyright © 1999, ZZP Online
-- free use for readers of Director Online
-- credit to Sebastiano <secondi / at /> 
-- for the conceptual start
property pForme1 
-- the vertexList of the initial shape
property pForme2 
-- the vertexList of the target shape
property pPasMorphing 
-- the incremental change per frame
property pMember1 
-- cast member with initial shape
property pMember2 
-- cast member with the target shape
property pMyMem 
-- the vector member on stage
property pFrames 
-- number of frames for morph animation
property pFrameCount 
-- current frame
property pFlag -
- on/off switch for morphing
on getPropertyDescriptionList me
  myMem = sprite(the currentSpriteNum).member
  pdlist = [:]
  addprop pdlist, #pMember1, [#comment:"Initial ¬
    Vector Shape member", #format:#member, ¬
  addprop pdlist, #pMember2, [#comment:"Target ¬
    Vector Shape member", #format:#member, ¬
    #default:myMem + 1]
  addprop pdlist, #pFrames, [#comment:"Frame ¬
    Duration for Morph", #format:#integer, ¬
  return pdlist
end getPropertyDescriptionList

on beginSprite me  
  pMyMem = sprite(the spriteNum of me).member
  pForme1=member(pMember1).vertexList * 1.0000
--  put "startList =" && pForme1
  pForme2=member(pMember2).vertexList * 1.0000
--  put "targetList =" && pForme2
  pPasMorphing= (pForme2-pForme1)/pFrames
--  put "increment =" && pPasMorphing
  pFlag = #stop
  pFrameCount = 0
on mouseUp me
  set pFlag = #morph
on enterFrame me
  if pFlag = #morph then
    if pFrameCount = pFrames - 1 then
      pMyMem.vertexList = pForme2
      pFlag = #stop
      pFrameCount = pFrameCount + 1
      -- put "pFrameCount =" && pFrameCount
    end if
  end if
end enterFrame

on hMorphAllee me
  pForme1 = pForme1 + pPasMorphing
  pMyMem.vertexList = pForme1
on reset me
  pMyMem.vertexList = pForme1
  pFrameCount = 0

In the beginSprite handler, we set some of the properties which weren't specified in the getPropertyDescriptionList handler. pForme1 and pForme2 are the vertexLists for the initial and target shapes, respectively. I multiply them by 1.0000 so that we can take full advantage of the fact that vertexLists can be float values. That's important so that we don't get rounding errors when calculating the incremental change. The real key to this whole behavior is that property called pPasMorphing. (It's one of the French variables that Sebastiano named.)

This property holds the list of points which are the incremental change per frame. The calculation is condensed to a single line, but it's the same as I described earlier: the difference in the two vertex lists, divided by the number of frames in the animation. The last steps in the beginSprite handler are to initialize our pFlag to #stop, and the pFrameCount to 0.

The mouseUp handler simply turns the morphing animation on by setting our pFlag to #morph. That means that on the next enterFrame event, the enterFrame handler will see that pFlag = #morph, and the morphing will begin. The enterFrame handler counts the number of frames in our animation. Each frame, it calls for the shape to be morphed by calling the hMorphAllee handler. This handler simply adds the incremental list (pPasMorphing) to pForme1, and then sets our on-stage shape member to that vertex list. The enterFrame handler counts frames until it reaches the last frame of the animation.

For the last frame, rather than having it morph the last time, it simply sets the shape to the target vertex list (pForme2). Finally, it sets our pFlag = #stop so that the morphing animation stops.

The last little handler there is simply there for the reset button. It resets our on-stage shape to the vertexList of our initial vector shape member. It also resets the frame count to zero.

A final warning. Since we're doing simple subtraction of one vertexList from the other, it is critical that each shape have the same number of vertexes. Further, each vertex point can have points for one or two "handles" which allow the shape to be curved. You must have exactly the same number of handles for corresponding points in the two shapes -- even if those handles are dragged on top of the vertex point (making their effect disappear.)

Great idea Sebastiano. Thanks for sending in your code and your question.

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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