Set precise scroll position when pinch-zoomed in - javascript

I'm creating a mapping app that places a marker image on a canvas and scrolls to it. I'm using the browser's pinch zooming and scrolling to zoom in/out of the map. However, I've noticed that there's some bizarre behavior, and I'm wondering how to get around it.
This is a little tough to explain, but here we go.
Let's imagine that you're at the standard zoom level on a webpage (you can't zoom out any further). Let's imagine that the area your browser window is showing is the "invisible box". There's some stuff you can see, and some stuff that's out of view (that you need to scroll to get to). Once you pinch-zoom in, the browser still pretends that your viewport is still at 100% zoom (i.e. Your browser is essentially cropping into that invisible box, but the invisible box stays in the same place.) Any JS on the page sees the scroll position as the same, no matter where you pan around within the invisible box. However, once you scroll to the edge, you start to push the edges of the invisible box. If you use JS to set the scroll position (window.scrollTo(xPos, yPos)), it sets the position of the invisible box, but the portion of the invisible box you see is still relative. This means that if you set the scroll position to (0,0) and your cropped-in view is not at the precise top left of the invisible box, the portion you see will NOT be at (0,0).
The issue I'm having is that I need to move the zoomed-in view to a specific spot. Since setting the position of the invisible box isn't really working, is there a way to force the browser to get rid of the invisible box, pinch-zoom all the way out, or maybe detect where the zoomed-in portion is within the invisible box? I'm stumped.

Related

A way to scroll up/down/left/right a static webpage

Remember pac-man where you go off the side of the screen and appear on the opposite side? This represents a spherical map represented in 2D.
I'm trying to get the same behavior for a "flat" webpage, so when the user scrolls down, the entire webpage, text, images, etc, moves with the scroll. When it reaches the bottom of the webpage, the "top" of the webpage comes in to view from the bottom, like pac-man.
The same would happen side-to-side or left-to-right, except instead of using the mouse wheel, they would hold down the middle mouse button and move the mouse left and right to pan side-to-side.
How to get the hotkeys to work doesn't concern me, I'm just looking for the "spherical panning" behavior, based on user control of the mouse or keyboard, not a predefined animation or movie.

Is there a way to prevent browsers from caching values like scroll position and zoom level?

I am designing an interactive web game that takes place entirely in the browser. It uses html5, and everything (including the elements) is part of the game world. Since this is the case, I need some pretty strict control over the positioning of my elements, scroll position, zooming, etc.
One particular level requires that an element be placed off screen (just outside the viewport) so that the user must scroll the page to find it. Unfortunately, after scrolling, the page seems to record the new width of the page including the originally unseen element. When the page is refreshed, the zoom level is adjusted to fit the entire screen with the hidden element into the viewport. This gives away the puzzle and ruins the level.
I know that browsers store information like scroll position so that when a user revisits the page they can pick up right where they left off. This is great for some things, but bad for my purposes. Is there a way to prevent this caching behavior of my browsers? Is there a way to get or set the zoom level of a page using JavaScript?
Currently I am using the code below to reset the scroll position right before the user leaves the page. It works pretty well, but the user can see the page scroll right before leaving.
window.addEventListener("beforeunload",function(event_){
window.scrollTo(0,0);
/* What I would love is if there were a way to do this: */
// window.zoomTo(1.0);
/* But I'm sure that's asking for too much. */
});
I managed to fix my problem by keeping the hidden element out of the html flow all together by setting its css position property to fixed. I simulate page scrolling by changing the elements style.left value with some custom touch event handlers. The page has no need to resize or zoom with the addition of the off screen element because fixed position elements do not effect layout.
This doesn't answer my question about resetting the zoom level, however, and I would still appreciate any insight anyone may have.

Prevent browser moving element when children are focused

I am implementing a simple map. The map consists of a viewport, and the map image itself, which is actually a div with a background image.
The viewport is relatively positioned and it's overflow is hidden, and the map image is absolutely positioned within the viewport.
The map can be moved with the mouse within the viewport and the map can also be zoomed (just increasing the size of the image as the image is a .svg)
The map has points on it which the user can hover over to get a description in a tooltip of the point. The points can also be focused by tabbing to them.
Points are children of the map image div and are absolutely positioned by percentage (to retain the correct position when the map is zoomed)
When a point is focused, I want to move the map so that the point is in the middle of the viewport. I have written the code for this and it works fine. However, if a point is outside of the viewport (not visible) then the browser automatically tries to move the map so the point is visible. I don't want it to do this, as it is interfering with the code I have written to animate the map move. This is nothing to do with scrolling.
I am using jQuery and have tried e.preventDefault() and return false; in the focus handler for the map points but neither work.
Is preventing this behaviour even possible?
Thanks in advance
I have found out that the scroll value of the map viewport was being set by the browser in order to bring the map point into view. As I am moving the map by setting it's top and left positions, this is what was causing the issue.
The solution was to add the .scroll() event listener to the viewport and just set the scrollTop and scrollLeft values to 0 when the event is triggered

How to zoom in on center of screen?

I'm trying to programmatically zoom in on what I'm seeing on the page, without changing which part of the content I'm seeing, regardless of where the scroll level is. I want this to be animated and pretty.
So I'm using $('body').animate({zoom:2.0}, 1000) to animate the zoom, but this has the irritating side effect of keeping the top of the visible window at the same point in the document (the browser's attempt to keep me where I was, actually, complete failure), so I need to basically continuously scroll to the same relative vertical center of the page as it's animating in order to get around that. How can that be done? I don't know how to do two things at once with animation--- I mean I could change multiple CSS properties at once, but how can I scroll?
Essentially, it needs to do something like this:
Call begin zoom animation:
1.Mark height level of any element that appears at center of window
2.Do one step of zoom animate
3.Scroll so that that element's height level relative to center of window is unchanged
4.Repeat until animation is complete
You can using Panzoom component for your goal.

Making overlay <div> that stays in position after zoom-resize using HTML-CSS only

I my working on the site that will have image gallery. Designer idea was to make buttons that switch photos be above the photos a bit.
Like this
Example http://img57.imageshack.us/img57/1253/showq.png
Currently I've made a javascript solution to this - it gets position of photo and applies absolute positioning to the button divs. There are some drawbacks - it works unstable in Opera and IE. Also I had to make some dirty haxx to make it stay in position after zooming. I wonder if there is a better way to do this, preferably without javascript.
you mean like here ? (dutch website, see photo browser in the center column at the top)
browser zooming works fine in browsers like firefox and safari because they zoom all the content and recorrect pixel-values. To make zooming work in ie(6) you'd need to style all in em's. But browser zooming is crappy for pixel data anyways…
Absolute positioning of the buttons (left 0 and right 0) is not a problem as long as the container element is positioned relative.
If I understand you correctly, you're trying to center those arrow buttons vertically in relation to the image. This is pretty easily accomplished with just CSS (no javascript required). Here's an example.
The basic idea is that you're using a couple of divs plus some absolute/relative positioning. There's an outer div that drops the top of the whole thing to the center of the parent element and then an inner div that pulls up your content so that the content is centered and not the top of the element.
A popular technique is to split the whole image into two huge (mostly transparent) links. The left half of the photo would take you to the previous image, the right to the next.
Of course you position you images of buttons appropriately and they would move around but I assume the problem you're finding is you have to keep moving your mouse to go through lots of images as the buttons move.... Well with this idea, you only need keep your mouse near the middle, and it should remain over the photo (and therefore a direction).
Example: http://gizmodo.com/photogallery/dreamhomespshop/1008251500
Mouse-over the image and you'll see it's active the complete way across. Not quite the same as your implementation, I'm sure, but the concept applies.

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