/**
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* Copyright (c) 2015, Facebook, Inc.
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* All rights reserved.
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*
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* This source code is licensed under the BSD-style license found in the
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* LICENSE file in the root directory of this source tree. An additional grant
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* of patent rights can be found in the PATENTS file in the same directory.
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*
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* @providesModule normalizeWheel
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* @typechecks
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*/
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'use strict';
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var UserAgent_DEPRECATED = require('./UserAgent_DEPRECATED');
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var isEventSupported = require('./isEventSupported');
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// Reasonable defaults
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var PIXEL_STEP = 10;
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var LINE_HEIGHT = 40;
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var PAGE_HEIGHT = 800;
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/**
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* Mouse wheel (and 2-finger trackpad) support on the web sucks. It is
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* complicated, thus this doc is long and (hopefully) detailed enough to answer
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* your questions.
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*
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* If you need to react to the mouse wheel in a predictable way, this code is
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* like your bestest friend. * hugs *
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*
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* As of today, there are 4 DOM event types you can listen to:
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*
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* 'wheel' -- Chrome(31+), FF(17+), IE(9+)
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* 'mousewheel' -- Chrome, IE(6+), Opera, Safari
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* 'MozMousePixelScroll' -- FF(3.5 only!) (2010-2013) -- don't bother!
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* 'DOMMouseScroll' -- FF(0.9.7+) since 2003
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*
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* So what to do? The is the best:
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*
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* normalizeWheel.getEventType();
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*
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* In your event callback, use this code to get sane interpretation of the
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* deltas. This code will return an object with properties:
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*
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* spinX -- normalized spin speed (use for zoom) - x plane
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* spinY -- " - y plane
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* pixelX -- normalized distance (to pixels) - x plane
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* pixelY -- " - y plane
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*
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* Wheel values are provided by the browser assuming you are using the wheel to
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* scroll a web page by a number of lines or pixels (or pages). Values can vary
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* significantly on different platforms and browsers, forgetting that you can
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* scroll at different speeds. Some devices (like trackpads) emit more events
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* at smaller increments with fine granularity, and some emit massive jumps with
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* linear speed or acceleration.
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*
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* This code does its best to normalize the deltas for you:
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*
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* - spin is trying to normalize how far the wheel was spun (or trackpad
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* dragged). This is super useful for zoom support where you want to
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* throw away the chunky scroll steps on the PC and make those equal to
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* the slow and smooth tiny steps on the Mac. Key data: This code tries to
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* resolve a single slow step on a wheel to 1.
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*
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* - pixel is normalizing the desired scroll delta in pixel units. You'll
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* get the crazy differences between browsers, but at least it'll be in
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* pixels!
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*
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* - positive value indicates scrolling DOWN/RIGHT, negative UP/LEFT. This
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* should translate to positive value zooming IN, negative zooming OUT.
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* This matches the newer 'wheel' event.
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*
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* Why are there spinX, spinY (or pixels)?
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*
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* - spinX is a 2-finger side drag on the trackpad, and a shift + wheel turn
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* with a mouse. It results in side-scrolling in the browser by default.
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*
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* - spinY is what you expect -- it's the classic axis of a mouse wheel.
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*
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* - I dropped spinZ/pixelZ. It is supported by the DOM 3 'wheel' event and
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* probably is by browsers in conjunction with fancy 3D controllers .. but
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* you know.
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*
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* Implementation info:
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*
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* Examples of 'wheel' event if you scroll slowly (down) by one step with an
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* average mouse:
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*
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* OS X + Chrome (mouse) - 4 pixel delta (wheelDelta -120)
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* OS X + Safari (mouse) - N/A pixel delta (wheelDelta -12)
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* OS X + Firefox (mouse) - 0.1 line delta (wheelDelta N/A)
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* Win8 + Chrome (mouse) - 100 pixel delta (wheelDelta -120)
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* Win8 + Firefox (mouse) - 3 line delta (wheelDelta -120)
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*
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* On the trackpad:
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*
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* OS X + Chrome (trackpad) - 2 pixel delta (wheelDelta -6)
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* OS X + Firefox (trackpad) - 1 pixel delta (wheelDelta N/A)
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*
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* On other/older browsers.. it's more complicated as there can be multiple and
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* also missing delta values.
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*
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* The 'wheel' event is more standard:
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*
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* http://www.w3.org/TR/DOM-Level-3-Events/#events-wheelevents
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*
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* The basics is that it includes a unit, deltaMode (pixels, lines, pages), and
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* deltaX, deltaY and deltaZ. Some browsers provide other values to maintain
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* backward compatibility with older events. Those other values help us
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* better normalize spin speed. Example of what the browsers provide:
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*
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* | event.wheelDelta | event.detail
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* ------------------+------------------+--------------
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* Safari v5/OS X | -120 | 0
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* Safari v5/Win7 | -120 | 0
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* Chrome v17/OS X | -120 | 0
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* Chrome v17/Win7 | -120 | 0
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* IE9/Win7 | -120 | undefined
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* Firefox v4/OS X | undefined | 1
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* Firefox v4/Win7 | undefined | 3
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*
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*/
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function normalizeWheel(/*object*/ event) /*object*/ {
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var sX = 0, sY = 0, // spinX, spinY
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pX = 0, pY = 0; // pixelX, pixelY
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// Legacy
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if ('detail' in event) { sY = event.detail; }
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if ('wheelDelta' in event) { sY = -event.wheelDelta / 120; }
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if ('wheelDeltaY' in event) { sY = -event.wheelDeltaY / 120; }
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if ('wheelDeltaX' in event) { sX = -event.wheelDeltaX / 120; }
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// side scrolling on FF with DOMMouseScroll
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if ( 'axis' in event && event.axis === event.HORIZONTAL_AXIS ) {
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sX = sY;
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sY = 0;
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}
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pX = sX * PIXEL_STEP;
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pY = sY * PIXEL_STEP;
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if ('deltaY' in event) { pY = event.deltaY; }
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if ('deltaX' in event) { pX = event.deltaX; }
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if ((pX || pY) && event.deltaMode) {
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if (event.deltaMode == 1) { // delta in LINE units
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pX *= LINE_HEIGHT;
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pY *= LINE_HEIGHT;
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} else { // delta in PAGE units
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pX *= PAGE_HEIGHT;
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pY *= PAGE_HEIGHT;
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}
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}
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// Fall-back if spin cannot be determined
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if (pX && !sX) { sX = (pX < 1) ? -1 : 1; }
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if (pY && !sY) { sY = (pY < 1) ? -1 : 1; }
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return { spinX : sX,
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spinY : sY,
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pixelX : pX,
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pixelY : pY };
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}
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/**
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* The best combination if you prefer spinX + spinY normalization. It favors
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* the older DOMMouseScroll for Firefox, as FF does not include wheelDelta with
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* 'wheel' event, making spin speed determination impossible.
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*/
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normalizeWheel.getEventType = function() /*string*/ {
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return (UserAgent_DEPRECATED.firefox())
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? 'DOMMouseScroll'
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: (isEventSupported('wheel'))
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? 'wheel'
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: 'mousewheel';
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};
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module.exports = normalizeWheel;
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