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