DHTML Jigsaw Puzzle: NN4; Creating the Pieces

The DHTML Lab Jigsaw Puzzle, Part III: NN4
creating the puzzle pieces

When the puzzle displays, we begin play by pressing the Break button which calls the breakUp() function. If the puzzle is a new puzzle, createPuzzle() is called. If createPuzzle() realizes that a new piece count is called for, it calls createPieces(). The logic of this flow has been discussed in detail in Part II.

function createPieces(){
    puzzPieces = puzzAcross * puzzDown;
    if (puzzPieces > piecesCreated) {
        makeStart = piecesCreated+1;
        for(i=makeStart; i<=puzzPieces; i++) {
            window.status = "Creating puzzle piece... " + i;
            eval("PIECE" + i  + " = new Layer(puzzWidth)");
        }
        piecesCreated = puzzPieces;
    }
    activeEl = eval("PIECE" + puzzPieces);
}
The createPieces() function reads as its previous IE incarnation. It
calculates how many pieces are necessary; if the ones already created
are not enough, it creates some more; it stores the amount of pieces
created so far and assigns the final piece created (the topmost in
z-order) to activeEl, so we can track it.
The new Layer Constructor
A first for these columns is the use of Navigator's new Layer
constructor to create a new positioned element on-the-fly. The complete
syntax is:
elementReference = new Layer(width);
This element (layer) will be created, added to the document.layers array, and any HTML written to it will
wrap at the width value. This type of element creation can be used only
after a page has fully loaded and displayed. It cannot be used in a
script outside of a function as, say, new Array can.
Once we have created the element, we can assign values to its various
properties to position it, clip it, write to it and so on. The one
property that will be missing that all other elements have is ID. We
cannot assign an ID value, but Navigator does supply one of its own
internally, in the form: _js_layer_layerNumber. The more on-the-fly
elements you create, the greater the layerNumber. This incrementation
persists throughout a browser session. It does not reinitialize with
every page load. So using this internal ID as an identifier is
worthless. We will always use the variables we assigned the constructor
to. In our example, these are PIECE1, PIECE2...etc. Just for your
reference, the first elements created with the constructor would have
internal IDs of _js_layer_1, _js_layer_2, etc.
Filling the Pieces
The major difference in createPuzzle() for Navigator is that every
puzzle piece has HTML written to it that loads a new image. Our other
alternative is to change the src property of the piece elements. This
however invokes the deadly "wysiwyg" problem, on reloads. The less said
about that, the better.
function createPuzzle() {
    if (!isCreated) { createPieces() };
    pieceWidth = puzzWidth/puzzAcross;
    pieceHeight = puzzHeight/puzzDown; 
    while (pieceCount <= puzzPieces) {
        pixT = topCount * pieceHeight;
        pixB = (topCount + 1) * pieceHeight;
        for (i=1; i<=puzzAcross; i++) {
            window.status = "Clipping image for piece... " + pieceCount;
            tempEl = eval("PIECE" + pieceCount);
            tempEl.document.write("<IMG WIDTH="+puzzWidth+" HEIGHT="+puzzHeight+" SRC="+puzzImage.src+">");
            tempEl.document.close();
            pixR = pieceWidth * i;
            pixL = pieceWidth * (i-1);
            tempEl.clip.top = pixT
            tempEl.clip.left = pixL
            tempEl.clip.right = pixR 
            tempEl.clip.bottom = pixB
            tempEl.clipLeft = pixL;
            tempEl.clipTop = pixT;
            pieceCount++
        }
        topCount++
    }
    if (isGrid) { setGrid() };    
    isNewPuzz = false;
    isCreated = true;
    pieceCount = 1;
    topCount = 0;
    window.status = "";
}
Therefore, createPuzzle() first establishes the width and height of
the pieces to be displayed. It then goes through the puzzle, one row at
a time, loading each piece element with an image, and clips it
accordingly. It assigns the left and top clip values to each element's
clipLeft and clipTop properties (for drag & drop use later). 
If grid use is turned on, setGrid() is called, and then the appropriate
values are assigned to our variables. When createPuzzle() exits, control is returned to the breakUp()
function that disperses the pieces.




Produced by Peter Belesis and
 
All Rights Reserved. Legal Notices.

Created: Nov. 27, 1997

Revised: Jan. 18, 1998
URL: https://www.webreference.com/dhtml/column10/puzzNScreate.html