// horizId only needed for horizontal scrolling
function dw_scrollObj(wndoId, lyrId, horizId) {
    if (!document.getElementById) return;
    var wn = document.getElementById(wndoId);
    this.id = wndoId; dw_scrollObj.col[this.id] = this;
    this.animString = "dw_scrollObj.col." + this.id;
    this.load(lyrId, horizId);
    
    if (wn.addEventListener) {
        wn.addEventListener('DOMMouseScroll', dw_scrollObj.doOnMouseWheel, false);
    } 
    //wn.onmousewheel = dw_scrollObj.doOnMouseWheel;
}

dw_scrollObj.col = {}; // collect instances
dw_scrollObj.defaultSpeed = dw_scrollObj.prototype.speed = 100; // default for mouseover or mousedown scrolling


// pseudo events 

dw_scrollObj.prototype.on_scroll_start = function() {}



dw_scrollObj.prototype.load = function(lyrId, horizId) {
    var wndo, lyr;
    if (this.lyrId) { // layer currently loaded?
        lyr = document.getElementById(this.lyrId);
        lyr.style.visibility = "hidden";
    }
    lyr = document.getElementById(lyrId); // hold this.lyr?
    this.lyr = lyr;
    lyr.style.position = 'absolute'; 
    this.lyrId = lyrId; // hold id of currently visible layer
    this.horizId = horizId || null; // hold horizId for update fn
    wndo = document.getElementById(this.id);
    this.y = 0; this.x = 0; this.shiftTo(0,0);
    this.maxY = (lyr.offsetHeight - wndo.offsetHeight > 0)? lyr.offsetHeight - wndo.offsetHeight: 0;
    this.wd = horizId? document.getElementById(horizId).offsetWidth: lyr.offsetWidth;
    this.maxX = (this.wd - wndo.offsetWidth > 0)? this.wd - wndo.offsetWidth: 0;
    lyr.style.visibility = "visible";
    this.ready = true; //this.on_load(); 
}

dw_scrollObj.prototype.shiftTo = function(x, y) {
    if (this.lyr) {
        this.lyr.style.left = (this.x = x) + "px"; 
        this.lyr.style.top = (this.y = y) + "px";
    }
}



// for mouseover/mousedown scrolling
dw_scrollObj.prototype.initScrollVals = function(deg, speed) {
    if (!this.ready) return; 
    if (this.timerId) {
        clearInterval(this.timerId); this.timerId = 0;
    }
    this.speed = speed || dw_scrollObj.defaultSpeed;
    this.fx = (deg == 0)? -1: (deg == 180)? 1: 0;
    this.fy = (deg == 90)? 1: (deg == 270)? -1: 0;
    this.endX = (deg == 90 || deg == 270)? this.x: (deg == 0)? -this.maxX: 0; 
    this.endY = (deg == 0 || deg == 180)? this.y: (deg == 90)? 0: -this.maxY;
    this.lyr = document.getElementById(this.lyrId);
    this.lastTime = new Date().getTime();
    this.on_scroll_start(this.x, this.y);  
    this.timerId = setInterval(this.animString + ".scroll()", 10);    
}

dw_scrollObj.prototype.scroll = function() {
    var now = new Date().getTime();
    var d = (now - this.lastTime)/1000 * this.speed;
    if (d > 0) { 
        var x = this.x + Math.round(this.fx * d); var y = this.y + Math.round(this.fy * d);
        if ( ( this.fx == -1 && x > -this.maxX ) || ( this.fx == 1 && x < 0 ) || 
                ( this.fy == -1 && y > -this.maxY ) || ( this.fy == 1 && y < 0 ) ) 
       {
            this.lastTime = now;
            this.shiftTo(x, y);
           // this.on_scroll(x, y);
        } else {
            clearInterval(this.timerId); this.timerId = 0;
            this.shiftTo(this.endX, this.endY);
            //this.on_scroll_end(this.endX, this.endY);
        }
    }
}

// when scrolling has ceased (mouseout/up)
dw_scrollObj.prototype.ceaseScroll = function() {
    if (!this.ready) return;
    if (this.timerId) {
        clearInterval(this.timerId); this.timerId = 0; 
    }
    //this.lyr = null; // discard ref?
    //this.on_scroll_stop(this.x, this.y); 
}