// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle. If not, see <http://www.gnu.org/licenses/>.
/*
* JavaScript to provide automatic scrolling, e.g. during a drag operation.
*
* Note: this module is defined statically. It is a singleton. You
* can only have one use of it active at any time. However, since this
* is usually used in relation to drag-drop, and since you only ever
* drag one thing at a time, this is not a problem in practice.
*
* @module core/autoscroll
* @copyright 2016 The Open University
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @since 3.6
*/
define(['jquery'], function($) {
/**
* @alias module:core/autoscroll
*/
var autoscroll = {
/**
* Size of area near edge of screen that triggers scrolling.
* @private
*/
SCROLL_THRESHOLD: 30,
/**
* How frequently to scroll window.
* @private
*/
SCROLL_FREQUENCY: 1000 / 60,
/**
* How many pixels to scroll per unit (1 = max scroll 30).
* @private
*/
SCROLL_SPEED: 0.5,
/**
* Set if currently scrolling up/down.
* @private
*/
scrollingId: null,
/**
* Speed we are supposed to scroll (range 1 to SCROLL_THRESHOLD).
* @private
*/
scrollAmount: 0,
/**
* Optional callback called when it scrolls
* @private
*/
callback: null,
/**
* Starts automatically scrolling if user moves near edge of window.
* This should be called in response to mouse down or touch start.
*
* @public
* @param {Function} callback Optional callback that is called every time it scrolls
*/
start: function(callback) {
$(window).on('mousemove', autoscroll.mouseMove);
$(window).on('touchmove', autoscroll.touchMove);
autoscroll.callback = callback;
},
/**
* Stops automatically scrolling. This should be called in response to mouse up or touch end.
*
* @public
*/
stop: function() {
$(window).off('mousemove', autoscroll.mouseMove);
$(window).off('touchmove', autoscroll.touchMove);
if (autoscroll.scrollingId !== null) {
autoscroll.stopScrolling();
}
},
/**
* Event handler for touch move.
*
* @private
* @param {Object} e Event
*/
touchMove: function(e) {
for (var i = 0; i < e.changedTouches.length; i++) {
autoscroll.handleMove(e.changedTouches[i].clientX, e.changedTouches[i].clientY);
}
},
/**
* Event handler for mouse move.
*
* @private
* @param {Object} e Event
*/
mouseMove: function(e) {
autoscroll.handleMove(e.clientX, e.clientY);
},
/**
* Handles user moving.
*
* @private
* @param {number} clientX X
* @param {number} clientY Y
*/
handleMove: function(clientX, clientY) {
// If near the bottom or top, start auto-scrolling.
if (clientY < autoscroll.SCROLL_THRESHOLD) {
autoscroll.scrollAmount = -Math.min(autoscroll.SCROLL_THRESHOLD - clientY, autoscroll.SCROLL_THRESHOLD);
} else if (clientY > $(window).height() - autoscroll.SCROLL_THRESHOLD) {
autoscroll.scrollAmount = Math.min(clientY - ($(window).height() - autoscroll.SCROLL_THRESHOLD),
autoscroll.SCROLL_THRESHOLD);
} else {
autoscroll.scrollAmount = 0;
}
if (autoscroll.scrollAmount && autoscroll.scrollingId === null) {
autoscroll.startScrolling();
} else if (!autoscroll.scrollAmount && autoscroll.scrollingId !== null) {
autoscroll.stopScrolling();
}
},
/**
* Starts automatic scrolling.
*
* @private
*/
startScrolling: function() {
var maxScroll = $(document).height() - $(window).height();
autoscroll.scrollingId = window.setInterval(function() {
// Work out how much to scroll.
var y = $(window).scrollTop();
var offset = Math.round(autoscroll.scrollAmount * autoscroll.SCROLL_SPEED);
if (y + offset < 0) {
offset = -y;
}
if (y + offset > maxScroll) {
offset = maxScroll - y;
}
if (offset === 0) {
return;
}
// Scroll.
$(window).scrollTop(y + offset);
var realOffset = $(window).scrollTop() - y;
if (realOffset === 0) {
return;
}
// Inform callback
if (autoscroll.callback) {
autoscroll.callback(realOffset);
}
}, autoscroll.SCROLL_FREQUENCY);
},
/**
* Stops the automatic scrolling.
*
* @private
*/
stopScrolling: function() {
window.clearInterval(autoscroll.scrollingId);
autoscroll.scrollingId = null;
}
};
return {
/**
* Starts automatic scrolling if user moves near edge of window.
* This should be called in response to mouse down or touch start.
*
* @public
* @param {Function} callback Optional callback that is called every time it scrolls
*/
start: autoscroll.start,
/**
* Stops automatic scrolling. This should be called in response to mouse up or touch end.
*
* @public
*/
stop: autoscroll.stop
};
});