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Prevent scroll on bodies (Matter.js)

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.

JavaScript scroll based animation is choppy on mobile

I have 2 divs (left and right) and i want to scroll the left based on the right.
https://jsfiddle.net/3jdsazhg/2/
This works fine on desktop, but when i change to mobile, it's not smooth anymore...
This can be noticed very easily, by changing
_left.style.top = _content.scrollTop - (_content.scrollTop * ratioLeftRight) + 'px';
to
_left.style.top = _content.scrollTop + 'px';
Where it should act as a fixed positioned div
I would like to know the exact reason why this isn't smooth... I know that it's not the animation. Simple animation on the div is smooth, the issue comes up when it's based on scroll.
How can i make this animation smooth?

It's probably choppy because it's being fired ALOT when being scrolled, in fact i'm pretty sure IOS mobile pauses the javascript execution whilst the user is scrolling.
Instead I'd suggest using an interval, you could tweak the time between each interval to what feels good for your use-case.
Although it may seem intensive that it's firing this logic every X millisecond when using the scroll event you could be firing the event off hundreds of times per second, which is going to be far more intensive and noticeable to a user using a device with limit processing power.
(function () {
var interval = null,
//Currently set at 0.4 seconds, play with the code
//and change this value to see what works best for
//this use-case
time_between_interval = 400;
setInterval(scrollLogic, time_between_interval);
function scrollLogic () {
//The function body of what you're assigning
//to the scroll event.
}
//I have omitted clearing the interval but you would want to do that, perhaps on page change, or something.
//clearInterval(interval);
})();

I finally managed to think out a solution.
From my point of view, i'm guessing the mobile view fires the scroll event less often and because we are scrolling the wrapper, we first scroll the whole page and then scroll back with js the left part and because it's different from the desktop version, this issue becomes visible...
The solution was to change the left side to fixed position, and substract from the top instead of adding to it.
_left.style.top = -(_content.scrollTop * ratioLeftRight) + 'px';

Allow vertical scrolling with touchstart when event.preventDefault enabled

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

Javascript support for touch without blocking browsers pinch support

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.

How to detect mobile Safari global orientation rotation animation

Hi I'm trying to trigger an event when mobile Safari rotates to a different orientation. I am aware of the orientationchange however this is not acceptable because it is called after the orientation rotation animation is played and the new orientation is set. I have an element that I need to hide before or during the animation.
I'm trying to capture the state before the orientation has changed particularly before the animation plays. I've tried applying events like webkitAnimationStart and animationstart to the window, document and document.body and none of them seem to be triggered. Hoping I'm overlooking something.

This is a problem occurring in almost every mobile browser as far as I saw and there is no straightforward solution for it.
A semi-official suggestion coming from the Chrome team posted on their blog under Unlock screen on device orientation change is to use deviceorientation and simulate what the browser does internally to figure out the orientation of the device:
var previousDeviceOrientation, currentDeviceOrientation;
window.addEventListener('deviceorientation', function onDeviceOrientationChange(event) {
// event.beta represents a front to back motion of the device and
// event.gamma a left to right motion.
if (Math.abs(event.gamma) > 10 || Math.abs(event.beta) < 10) {
previousDeviceOrientation = currentDeviceOrientation;
currentDeviceOrientation = 'landscape';
return;
}
if (Math.abs(event.gamma) < 10 || Math.abs(event.beta) > 10) {
previousDeviceOrientation = currentDeviceOrientation;
// When device is rotated back to portrait, let's unlock screen orientation.
if (previousDeviceOrientation == 'landscape') {
screen.orientation.unlock();
window.removeEventListener('deviceorientation', onDeviceOrientationChange);
}
}
});
The particular use case the Chrome team used this code for is to get the device's orientation after using screen.orientation.lock (which disable orientation change events).
This can be generalized as a substitute for orientation change events giving you a slight time-advantage before the animation kicks in.
The tricky part is figuring out the right angle range for which the browser decides to switch orientations (you don't want to start your animation when the browser doesn't actually switch orientations).
One way to solve this is to take complete control over orientation changes using screen.orientation.lock where essentially you set the threshold and lock the orientation accordingly.
However since the world isn't perfect, screen.orientation.lock only works in fullscreen mode or in standalone web-apps... If you intend your app to be a fullscreen experience or a standalone web-app then you're in luck.