I have a little web gallery that I added swipe navigation to for mobile browsers. I did it with pretty simple touchstart/touchmove/touchend event tracking.
The problem is that when I try to pinch zoom in the browser window it fails if any finger starts in the element I added the touch event handlers to, I'm guessing from the calls to preventDefault.
Is there a way I can track the touch events for navigating my images without blocking the zoom in and out feature of the browser? I don't mind blocking single finger scrolling if it's over my element, but I want to allow the pinch zooming.
Here's the code:
function addDragHandlers(eventDivId) {
var startX, endX;
var slides = $('#'+eventDivId);
slides.bind('touchstart', function(e) {
e.preventDefault();
startX = e.pageX;
endX = startX;
});
slides.bind('touchmove', function(e) {
e.preventDefault();
endX = e.pageX;
});
slides.bind('touchend', function(e) {
e.preventDefault();
if ( endX - startX < 0) {
// go to next image
} else if ( endX - startX > 0) {
// go to previous image
} else {
// do click action
}
}
});
}
What you want is ongesturestart, ongesturestart move and end work the same as on touch but for more than one finger. From their you can add a listener for:
event.stopPropagation();
to prevent "preventDefault()" from propagating in.
I wanted this to work on Android so I didn't want to use gesture events, which I have read are only on iOS - though I have no android to test that claim.
I then looked at a bunch of javascript gesture libraries which try to make gesture support easy. Unfortunately none of them worked well enough for my purposes.
So I ended up using touch handlers on the body to track all the touches on the page and then a custom heuristic to determine whether to use the touch to navigate the gallery or to use it to scroll/pinch the page.
It's still not perfect. If you start by touching my gallery element and then touching outside it the pinch doesn't work.
As an aside, the "TouchSwipe" jquery library has an incredibly well-designed and flexible API, but with the configuration I needed, tracking only horizontal swipes on my element, it was too quirky under iOS6 and hasn't been updated for a few weeks. If you are looking into this sort of challenge and it's a few months from now I'd recommend checking the updates for that plugin.
Related
I have created a web interface where the user can drag and drop SVG elements on screen. I am struggling with the performance of moving the SVGs via touch events on iPhone iOS using the webkit engine.
Everything is fine on desktop browsers and on Android phones that I could get hold of, but iOS on iPhones shows very bad performance (seems fine on iOS on one iPad that I could get hold of, but it sometimes leaves some traces of the SVG after moving).
There seems to be a delay before the touchstart event kicks in after touching the device and a delay before the touchend event is triggered after releasing the touch: An audio sample (already loaded) that is supposed to play after picking up or dropping the element plays with a delay of ~1.5 seconds. The touchmove event seems to be handled smoothly though - no delay with moving the SVG (after touchstart has ended).
I have already checked iOS Delay between touchstart and touchmove? - but the site that's linked to doesn't help me. I fail to get the scroll event on any element (window, document, svgElement) - and even if I did, I wouldn't know how this could help me.
I assumed the the issue might be related to the size of the base64 encoded background image that the SVGs are using, but reduzing that size even dramatically didn't help.
I read about some 300-350ms delay that iOS might have if there's no "fast tap" mode set, but a) the delay between touching/releasing the screen and playing the audio is longer than 350ms (rather 1.5 seconds) and b) playing with the touch-action CSS property did not help. (Eliminate 300ms delay on click events in mobile Safari)
I am really not sure if I am doing anything wrong (very well possible!) or if the webkit engine on (iPhone) iOS is simply so bad (compared to e.g. Blink on Android that runs flawlessly) that it cannot handle to render/move SVGs? Testing this is particularly iffy, because Browserstack doesn't issue TouchEvents properly and I never succeded to hook up the single physical iOS device that I have (a 2015 iPod Touch) to my Linux machine for remote debugging (while it's very simple for Android on Chromium). I'd really be grateful for hints!
An SVG roughly follows the following pattern (some attributes like viewBox, stroke-width etc. omitted):
<svg>
<defs><pattern id="SOME_ID"><img href="data:SOME_BASE64_ENCODED_IMAGE" /></pattern></defs>
<path fill="url(#SOME_ID)" d="SOME_SIMPLE_PATH"></path>
<path d="SOME_OTHER_SIMPLE_PATH"></path>
</svg>
The SVGs can be moved by MouseEvent or TouchEvent using the following logic:
// this.svgElement is the DOM element within the class
this.svgElement.addEventListener('touchstart', this.handleMoveStarted, false);
this.svgElement.addEventListener('mousedown', this.handleMoveStarted, false);
// Keep track of start position and add move/end listeners
handleMoveStarted(event) {
event.preventDefault();
event.stopPropagation();
if (event.type === 'touchstart') {
this.moveInitialX = event.touches[0].clientX;
this.moveInitialY = event.touches[0].clientY;
this.svgElement.addEventListener('touchmove', this.handleMoved, false);
this.svgElement.addEventListener('touchend', this.handleMoveEnded, false);
}
else {
// Same principle for event.clientX/Y and MouseEvent
}
// Callback to play audio here
}
// Compute delta position and update
handleMoved(event) {
event.preventDefault();
event.stopPropagation();
let deltaX = 0;
let deltaY = 0;
if (event.type === 'touchmove') {
deltaX = this.moveInitialX - event.touches[0].clientX;
deltaY = this.moveInitialY - event.touches[0].clientY;
this.moveInitialX = event.touches[0].clientX;
this.moveInitialY = event.touches[0].clientY;
}
else {
// Same principle for event.clientX/Y and MouseEvent
}
this.svgElement.style.left = `${parseFloat(this.svgElement.style.left) - deltaX}px`;
this.svgElement.style.top = `${parseFloat(this.svgElement.style.top) - deltaY}px`;
}
// Used to remove listeners on tochenend/mouseup
handleMoveEnded(event) {
event.preventDefault();
event.stopPropagation();
this.svgElement.removeEventListener('mousemove', this.handleMoved);
this.svgElement.removeEventListener('touchmove', this.handleMoved);
this.svgElement.removeEventListener('mouseup', this.handleMoveEnded);
this.svgElement.removeEventListener('touchend', this.handleMoveEnded);
// Callback to play audio here
}
I have investigated this issue some more, and it turns out that it's not the SVG dragging that's causing the huge delay in iOS, but it's the callbacks that follow. It seems that iOS has quite some trouble with playing plain HTML5 audio in a timely (real-time) fashion and I'll have to revert to some other solution (HTML 5 audio .play() delay on mobile).
Background
I'm trying to achieve something, but it's really driving me crazy. So any help would be appreciated!
I've created a scene in Matter.js that will be placed in a container further down on the page. I want the visitor to be able to interact with the scene, dragging and dropping the bodies. But allowing interaction creates the problem where Matter.js prevents the user from scrolling whenever the mouse is over the canvas.
So to work around this, I'm using the following code:
mouseConstraint.mouse.element.removeEventListener("mousewheel", mouseConstraint.mouse.mousewheel);
mouseConstraint.mouse.element.removeEventListener("DOMMouseScroll", mouseConstraint.mouse.mousewheel);
This makes it possible for the user to scroll through the page and still being able to interact with the scene by clicking and dragging the bodies, as it's only the scroll event listeners that are being removed. At least on desktop.
The problem
However, on mobile, the touch event is the event that makes it possible for the user to scroll on the page, so that would require me to also remove the touchmove, touchstart and touchend event listeners from the mouse constraint in Matter.js. Like this:
mouseConstraint.mouse.element.removeEventListener('touchmove', mouseConstraint.mouse.mousemove);
mouseConstraint.mouse.element.removeEventListener('touchstart', mouseConstraint.mouse.mousedown);
mouseConstraint.mouse.element.removeEventListener('touchend', mouseConstraint.mouse.mouseup);
And here's where the problem occurs. If I remove the touch events, the user can scroll by the canvas, but the user can't interact with the scene as that requires the touch events to be activated.
So I'm wondering if there is any way to have the touch events added but only allow them to work on certain bodies in the scene? I've found that I can use mouseConstraint.body as a boolean in order to know if a body has been clicked/touched or not. Could this be used in some way with this as a base?:
Matter.Events.on(mouseConstraint, "mousedown", function(event) {
if (mouseConstraint.body) {
console.log("Body clicked!");
}
});
This is the solution that I came up with. It's not perfect, but it's better than nothing.
let touchStart;
mouseConstraint.mouse.element.addEventListener('touchstart', (event) => {
if (!mouseConstraint.body) {
touchStart = event;
}
});
mouseConstraint.mouse.element.addEventListener('touchend', (event) => {
if (!mouseConstraint.body) {
const startY = touchStart.changedTouches[0].clientY;
const endY = event.changedTouches[0].clientY;
const delta = Math.abs(startY - endY);
if (delta > 80) {
window.scrollTo(0, 600);
}
}
});
You listen for the touch start event and store that in a variable. Then in the touchend event you check if the swipe is large enough to constitute a scroll, then scroll to the content.
I am trying to build a one touch game on HTML5 canvas. It's a running game made with the help of this tutorial:
http://blog.sklambert.com/html5-game-tutorial-game-ui-canvas-vs-dom/
I changed the existing controls from space bar to a mouse click. It works perfectly across all the platforms except Android devices mobile browsers.
In Android devices, the touch makes the user jump. If there is a long hold in the touch, the user keeps jumping even when the touch is released. This problem does not happen in iPhones or iPads or desktops.
Can I make a Javascript function where a mouse down for a certain number of seconds is cut ? Something like:
if(mousedown for 1sec)
mouseup;
Let me know if you can think of another approach.
You can use touch events rather than mouse for touch enabled devices. Refer: https://developer.mozilla.org/en-US/docs/Web/API/Touch_events/Using_Touch_Events
function is_touch_device() {
/* Function code taken from http://stackoverflow.com/a/4819886/3946520 */
return 'ontouchstart' in window // works on most browsers
|| navigator.maxTouchPoints; // works on IE10/11 and Surface
};
if(is_touch_device()) {
canvas.addEventListener('touchstart', handleTouchStart, false);
canvas.addEventListener('touchend', handleTouchEnd, false);
}
else {
// Bind Mouse Events
}
function handleTouchStart(e) {
// This code runs when user touches the canvas i.e. on touch start
}
function handleTouchEnd(e) {
// This code runs when user removes finger from canvas i.e. on touch end
}
Also note that there can be scenario where the user puts two or more fingers on the canvas. Each of them will fire 'touchstart' event. So you'll have to handle that.
You can refer to http://www.javascriptkit.com/javatutors/touchevents.shtml for a good tutorial on touch events.
I am currently having an issue in allowing vertical scrolling when event.preventdefault is enabled.
I am trying to add swipe functionality to my mobile page, I have tried may frameworks like hammer.js, swipe.js etc, and all of them require event.preventDefault enabled to detect left and right swipes.
When event.preventDefault is enabled, the swipes detect perfectly, however you lose the ability to vertical scroll when you are on that element. i.e you cannot move the screen up or down on a mobile device, when your finger starts on the swipe element.
I have tried building my own little script which works well, but again has the issue of vertical scrolling, that is an issue.
var el = document.getElementById('navigation');
el.ontouchstart = function(e){
e.preventDefault();
el.innerHTML = "touch start";
};
el.ontouchend = function(e){
el.innerHTML = "touch end";
};
el.ontouchmove = function(e){
el.innerHTML = "touch moved";
};
el.ontouchcancel = function(e){
el.innerHTML = "touch cancel";
};
Any ideas???
It's a common issue where you want the native browser behaviour to work alongside the interaction behaviour that people come to expect from a touchscreen device.
If you want to use a library you might need to hack it open as you WILL need to prevent the defaults to prevent the page from jumping all over the place when using touch events, but at other times you want to omit it as you want to prevent the page from remaining in a static position, obscuring other content.
Ideally you want add a clause to the handler that instructs them whether or not to prevent the default behaviour the browser executes upon receiving the event.
Swiping for instance, is a behaviour that should occur in a short time frame (if you are taking for instance one whole second in moving your finger from one area to the other instead of, let's say, 120 ms, you're not actually swiping, but dragging. Thinking about time frames may help you here, for instance:
var threshold = 150, interactionStart;
el.ontouchstart = function( e )
{
// store timestamp of interaction start
interactionStart = +new Date;
};
el.touchmove = function( e )
{
// get elapsed time in ms since start
var delta = +new Date - interactionStart;
if ( delta > threshold )
{
e.preventDefault();
}
else {
// super cool magic here
}
};
Whether 150 ms is the threshold you want depends on the action, as you see there is no fixed answer for your question as the actual implementation depends on what your application needs in terms of touch interactions.
You could also consider not blocking the events default when the user is scrolling more along the vertical axis (i.e. compare whether the delta position of the events Y offset (relative to the start Y offset) is larger than the events X offset (relative to the start X offset) to detect whether the users is moving left or right or up or down (for instance if you have a carousel that can swipe horizontally (where the default behaviour is blocked so the page won't move up/down during the horizontal scroll) but want the page to scroll vertically when the user is obviously dragging the page among the vertical axis).
The library jquery.touchSwipe solves that.
The library: https://github.com/mattbryson/TouchSwipe-Jquery-Plugin
An example page where swiping and scrolling are combined: http://labs.rampinteractive.co.uk/touchSwipe/demos/Page_scrolling.html
I am working on a touch based JS application, I've studied Flex and Royal slider as examples. I noticed that both sliders acting similarly when getting touchmove event:
var started,touched ;
el.bind('touchstart',function(e){
started = Number(new Date()) ;
// Get pageX and pageY etc...
}) ;
el.bind('touchmove',function(e){
touched = Number(new Date()) ;
if (started-touched > 500) {
// Handle touch moves etc...
}
}) ;
My JS app works seamless without these, but why do they need to do this? Why they are waiting 500ms to get move datas?
I believe this is some kind of sensitivity setting. You only want to register a touch-move (drag) event if the user has been moving his or her finger across the device for at least 500ms (in this example).
This could be useful to differentiate between taps and drags. Otherwise, if the user would slightly move his/her finger when clicking, for example, a button, the app would also register a drag. As some controls accept both events, this could lead to erroneous behaviour.