I'm making a simple website, that doesn't have to be super fast and performant, I'm only focused on some nice design elements. One of those design elements is blur that is applied to statically positioned background "under" some containers, that move when scrolling. This example should be self-explanatory. (I hope it's OK to share the website itself. It's just a personal website, no advertisement intended.)
This could be done with CSS filters and some moving background-position on the containers. However, the background is not an image but a canvas element. (For now, it's just an image redrawn into the canvas, but it will be generated algorithmically.) So my approach is: The blurred containers contain a canvas as their background and the content of the background canvas is redrawn with a filter applied on every scroll and resize event. As I said, this doesn't have to be fast and probably no other complex computations will be performed on the client-side, but a smooth user experience is important.
(If needed, I will provide relevant parts of the code.)
My question is: I noticed, that when scrolling with a scrollbar, it renders very smoothly, but when scrolling with a mouse wheel it probably just can't redraw the background fast enough and it looks as if the blurred background falls a bit behind. When swiping on a touch screen, it gets even worse and the blurred background is always behind the actual background. The fact that it's able to keep up when scrolling with a scrollbar makes me think that the problem is not with the canvas redrawing approach but with handling the events. Is there any way to handle the scroll event in such a way, that the performance will always be as good as when scrolling with a scrollbar? Maybe it's not even about performance, but rather that mouse wheel and swipe scrolling don't trigger the event as frequently, which causes these "gaps" when the canvas isn't being redrawn? If so, I should probably implement the redrawing in such a way, that it accounts for the delta of the scroll event and just draws the blurred background several times in between the events.
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I'm using a library called ParticlesJS for part of the background of my website - this library dynamically generates a canvas element sized according to its parent, and fills it with animated particle effects, creating a neat effect. With that said, I have run into some practical issues when trying to use it as the background:
If the canvas element is the same size as the content, the visuals become pixelated and distorted if the height changes, such as with the addition of new content. Reloading the library is not a solution to this as it creates a visually distracting effect.
If the canvas element is an arbitrary extreme height and not sized according to the content (with the overflow simply hidden), the performance of the website suffers, as the library consumes excessive CPU power.
If the canvas element is simply given a fixed position in CSS, performance is good and it sticks, but it looks out of place as everything behind it moves during scrolling.
After some consideration, it seems like the best way to make it work is to give it a modest size (like 200% page height), and then make it repeat infinitely during scrolling - performance would be acceptable, and there wouldn't be any distortion. However, I can't find any way to do this - I'm aware that there's a background-repeat property in CSS, but that seems to only work for images.
Is there any way to do what I'm trying to accomplish? Both CSS and JS based answers are welcome.
After some trial and error, it looks like the only means of accomplishing what I'm trying to do is as follows:
Create 3 or so background divs, each the size of the view port, and stack them vertically
Record user scrolling activity, and set a trigger for when a user has scrolled a height equal to the height of the view port
when the trigger is hit, place the div that just left the view port at the end of the list, and insert an empty spacer div where it used to be
If done correctly, this creates an effect where the user is apparently scrolling through an infinite background, when it's really just the same 3 or so divs being shuffled over and over. Going in reverse is the same principle.
Not sure how to make this work with in a system that also has scroll position restoration, but it could probably be done by waiting for page loads and then dynamically inserting enough spacers to move the background divs to the appropriate position in the view port.
The downside to using animated effects that rely on viewport dimensions is that the user may resize the browser and wreck your animation so you have no choice but to catch any viewport resizing in which case you may have to reload everything or recalculate!
You can't have the cake and the cherry on top unfortunately, so you'll either have to abandon the idea of "impressive effects" because they are impractical or take action...
document.body.onresize=function(){Adjustments();};
function Adjustments(){
var W=Container.offsetWidth, H=Container.offsetHeight;
// You've now got the new resolution so go for your life!
}
I have a fixed element which covers the entire screen and need scrolling.
IOS has what people call 'rubbing banding' for an example of this behavior you can take a look at these gifs:
http://blog.christoffer.me/six-things-i-learnt-about-ios-safaris-rubber-band-scrolling/
The problem is that when rubber banding occurs and pulls my fixed element down(revealing the content it overlays) there is a chance a users finger might end up on the content which is being overlay-ed.
When this happens all touchmove event will trigger not on my fixed element that covers the screen but on the body that my fixed element is overlaying.
I know you can prevent the body from scrolling in a maner like this:
body.noscroll{
position:fixed;
overflow:hidden;
}
But this is a solution to prevent scrolling.
This is not the solution because once the touchmove event has triggered on the overlay-ed content once, it will only stop if a user removes their finger from the screen.
In short a user might scroll my fixed element, reach the top making the rubber banding kick in and swipe on the body instead of the fixed element because the rubber banding reveals the body.
Even if the element pops back into place after the rubber banding has taken place the touchmove event is still stuck on the body element until the user removes his finger from the screen.
I am pretty lost on what to do here. Somehow disabling the touchmove event for the body seems like a good idea but my fixed element is inside there and it still needs scroll abilities.
Any thoughts or tips on how to handle this?
Edit:
A simply jsfiddle:
https://jsfiddle.net/pq88zLLx/1/
This only works on IOS though and only if you swipe into the content that the rubber banding is revealing.
There really is not a good solution for dealing with a fixed element that has scrolling inside of it on mobile browsers.
I have not tested other browsers besides Safari but I've learned that other browsers are not too fond of this combination either.
The best and most flexible solution is to make your full screen elements absolute positioned. This will fix common issues with swiping and positioning.
But what if my element is in a relative container?
Then you are out of luck and need to grab your element, remove it from the dom and place it up as high in the dom as you can when you are opening your fullscreen element.
Afterwards you need to place your element back in it's original position. They best way I know of to do this, is to leave behind a placeholder for you to append/prepend to. The dom has no method your giving you the exact location of an element therefore if you don't want the order of elements to change you are forced to do this.
Feel free to leave comments or suggestions on this answer if you feel like improvements can be made.
There's quite a few questions about this where the solution provided is to just set the top left and top down values of the image to the position of the mouse/touch, however what I want to do is to have an actual dragging movement. Regardless as to where on the canvas I press, if I drag my finger to the right x pixels, I want the image to move to the right x pixels. Same goes with left, up, and down.
I'm at a complete loss as to where to even start with this. I will be handling mobile touch events, so I feel like using canvas.addEventListener('touchmove') would be the best option, but I'm not sure.
I already have the canvas repainting and everything handled, just really need help with the logic for dragging the image in real time, instead of just snapping it into position.
Get the point where the interaction starts (touchstart) and use it to calculate how much the finger moved on the screen (in the touchmove callback) and add it to the image position (also in touchmove).
PS: Also I recommend using something like PIXI JS for canvas/WebGL stuff ... unless you need a custom solution.
Okay this is a rather complicated setup/question so I will try to explain it as clear as possible. Right now stellar parallax is working great on my site with no issues whatsoever. this was accomplished by setting the responsive property in stellar.js to true which makes it so that the background image follows the div when you resize the window. Because the issue before was that resizing the window was bad because stellar vertically aligns the background images in a certain way so if you resized the window the div in question might end up in an area where the background is repeating or in an empty spot(if you had no repeat on), it just wouldnt be aligned with the background image anymore. Responsiveness=true fixed this.
However here is the new issue. I have a section on my website where 3 divs are set to display: none by default. 3 buttons, respectively, toggle their display. Toggling their display makes their parent div much longer therefore pushing the rest of the content of the page further down. This pushes the stellar divs out of position with their background images again and i can see areas where the image repeats or are blank(if you have no repeat). However if you resize the window after you toggled the three hidden divs, the stellar divs will automatically fix itself and realign the images as a result of it picking up the responsiveness. I was wondering if there was anyway perhaps I could make toggling the hidden divs trigger this realignment without the user having to resize the window(he/she wouldnt know he/she had to anyway)?
Perhaps a way to refresh a specific part of the page(the stellar divs)? Or perhaps a function to resize the window by like a pixel or even 0 pixels just to trigger the responsiveness?
Thanks in advance, I hope everything makes sense.
I'm building a web app that has a grid of many small scrollable divs (actually, Ace editors), and this grid has enough elements that it is larger than the window. When a user begins scrolling over empty space, I want them to be scrolling the window itself; when a user begins scrolling inside a grid element, I want them to scroll the div contents there. The thing is, if a user begins scrolling over empty space, and then scrolls such that their mouse goes over a grid element, that scrollable div captures all the scrolling events, interrupting the user's flow over the grid and "trapping" them inside the grid element.
I can't manually capture onmousewheel events, since AFAIK there's no way to capture horizontal mouse wheel movement separately from vertical, and I want users on Mac OS X to be able to scroll in all directions. I've thought about using JS to add an invisible div with a very high z-index on the first onscroll event, and removing it as soon as onscroll events aren't triggered for a certain period of time. Haven't yet coded this up, but I'm wondering if there's a better solution, or if there are any potential pitfalls that I haven't thought of. Any help or advice would be great! Thanks!
I think a solution for this would be incredibly difficult due to browser support, and the actual solution, which would probably be something like calculating the scroll, backtracking the div, and applying the scroll to the page.
You could do something like this:
$('div').scroll(function(e){
// figure out how much it has scrolled
window.scrollBy(0,howmuch);
});
I don't recommend this solution in the slightest though, I think the better option would be to set the divs to overflow:hidden; and pick up a solid scroll plugin, and use that to customize the scroll behavior on the divs.