source: Dev/trunk/src/client/dojo/dnd/autoscroll.js

define(["../_base/lang", "../sniff", "../_base/window", "../dom-geometry", "../dom-style", "../window"],
        function(lang, has, win, domGeom, domStyle, winUtils){

// module:
//              dojo/dnd/autoscroll

var exports = {
        // summary:
        //              Used by dojo/dnd/Manager to scroll document or internal node when the user
        //              drags near the edge of the viewport or a scrollable node
};
lang.setObject("dojo.dnd.autoscroll", exports);

exports.getViewport = winUtils.getBox;

exports.V_TRIGGER_AUTOSCROLL = 32;
exports.H_TRIGGER_AUTOSCROLL = 32;

exports.V_AUTOSCROLL_VALUE = 16;
exports.H_AUTOSCROLL_VALUE = 16;

// These are set by autoScrollStart().
// Set to default values in case autoScrollStart() isn't called. (back-compat, remove for 2.0)
var viewport,
        doc = win.doc,
        maxScrollTop = Infinity,
        maxScrollLeft = Infinity;

exports.autoScrollStart = function(d){
        // summary:
        //              Called at the start of a drag.
        // d: Document
        //              The document of the node being dragged.

        doc = d;
        viewport = winUtils.getBox(doc);

        // Save height/width of document at start of drag, before it gets distorted by a user dragging an avatar past
        // the document's edge
        var html = win.body(doc).parentNode;
        maxScrollTop = Math.max(html.scrollHeight - viewport.h, 0);
        maxScrollLeft = Math.max(html.scrollWidth - viewport.w, 0);     // usually 0
};

exports.autoScroll = function(e){
        // summary:
        //              a handler for mousemove and touchmove events, which scrolls the window, if
        //              necessary
        // e: Event
        //              mousemove/touchmove event

        // FIXME: needs more docs!
        var v = viewport || winUtils.getBox(doc), // getBox() call for back-compat, in case autoScrollStart() wasn't called
                html = win.body(doc).parentNode,
                dx = 0, dy = 0;
        if(e.clientX < exports.H_TRIGGER_AUTOSCROLL){
                dx = -exports.H_AUTOSCROLL_VALUE;
        }else if(e.clientX > v.w - exports.H_TRIGGER_AUTOSCROLL){
                dx = Math.min(exports.H_AUTOSCROLL_VALUE, maxScrollLeft - html.scrollLeft);     // don't scroll past edge of doc
        }
        if(e.clientY < exports.V_TRIGGER_AUTOSCROLL){
                dy = -exports.V_AUTOSCROLL_VALUE;
        }else if(e.clientY > v.h - exports.V_TRIGGER_AUTOSCROLL){
                dy = Math.min(exports.V_AUTOSCROLL_VALUE, maxScrollTop - html.scrollTop);       // don't scroll past edge of doc
        }
        window.scrollBy(dx, dy);
};

exports._validNodes = {"div": 1, "p": 1, "td": 1};
exports._validOverflow = {"auto": 1, "scroll": 1};

exports.autoScrollNodes = function(e){
        // summary:
        //              a handler for mousemove and touchmove events, which scrolls the first available
        //              Dom element, it falls back to exports.autoScroll()
        // e: Event
        //              mousemove/touchmove event

        // FIXME: needs more docs!

        var b, t, w, h, rx, ry, dx = 0, dy = 0, oldLeft, oldTop;

        for(var n = e.target; n;){
                if(n.nodeType == 1 && (n.tagName.toLowerCase() in exports._validNodes)){
                        var s = domStyle.getComputedStyle(n),
                                overflow = (s.overflow.toLowerCase() in exports._validOverflow),
                                overflowX = (s.overflowX.toLowerCase() in exports._validOverflow),
                                overflowY = (s.overflowY.toLowerCase() in exports._validOverflow);
                        if(overflow || overflowX || overflowY){
                                b = domGeom.getContentBox(n, s);
                                t = domGeom.position(n, true);
                        }
                        // overflow-x
                        if(overflow || overflowX){
                                w = Math.min(exports.H_TRIGGER_AUTOSCROLL, b.w / 2);
                                rx = e.pageX - t.x;
                                if(has("webkit") || has("opera")){
                                        // FIXME: this code should not be here, it should be taken into account
                                        // either by the event fixing code, or the domGeom.position()
                                        // FIXME: this code doesn't work on Opera 9.5 Beta
                                        rx += win.body().scrollLeft;
                                }
                                dx = 0;
                                if(rx > 0 && rx < b.w){
                                        if(rx < w){
                                                dx = -w;
                                        }else if(rx > b.w - w){
                                                dx = w;
                                        }
                                        oldLeft = n.scrollLeft;
                                        n.scrollLeft = n.scrollLeft + dx;
                                }
                        }
                        // overflow-y
                        if(overflow || overflowY){
                                //console.log(b.l, b.t, t.x, t.y, n.scrollLeft, n.scrollTop);
                                h = Math.min(exports.V_TRIGGER_AUTOSCROLL, b.h / 2);
                                ry = e.pageY - t.y;
                                if(has("webkit") || has("opera")){
                                        // FIXME: this code should not be here, it should be taken into account
                                        // either by the event fixing code, or the domGeom.position()
                                        // FIXME: this code doesn't work on Opera 9.5 Beta
                                        ry += win.body().scrollTop;
                                }
                                dy = 0;
                                if(ry > 0 && ry < b.h){
                                        if(ry < h){
                                                dy = -h;
                                        }else if(ry > b.h - h){
                                                dy = h;
                                        }
                                        oldTop = n.scrollTop;
                                        n.scrollTop  = n.scrollTop  + dy;
                                }
                        }
                        if(dx || dy){ return; }
                }
                try{
                        n = n.parentNode;
                }catch(x){
                        n = null;
                }
        }
        exports.autoScroll(e);
};

return exports;

});