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