jQuery Hover Over Image Content Only and Not Alpha - javascript

Perhaps the title isn't great, but I had a little trouble with the wording...
Basically, is it possible to have jQuery's hover only fire over the actual content of a png with an alpha channel.
So in the image below;
http://i.imgur.com/3kO7v.png
Only fire on the rectangle and not the alpha channel which make up the rest of the document bounds...
I've tried the obvious $('obj').hover(function(){stuff}) but this fires on the alpha channel too...
The final implementation of this will be for more complex shapes than just a rotated square, so css3 tricks are out for the primary basis, but could be used with a back-up/shim, plus I need to support IE7 and ipad,iphone,ipod....
If there is a CSS2 solution then that would be suitable too. Also any real guidance on this issue is more than welcome.
My backup for this will be to have an empty div, display block and position it over the shape and then use that. This will obviously not be ideal for the less square objects.
Any hits or tips are more than welcome.
Thank you

Yes it is possible depending on the stacking context of your elements. Keep in mind that when you do a focus over any particular element on a page, that you are actually focusing all other elements within the same stacking context.
So what you could do is either stop the event from bubbling up the stack (if the element you want to "hover" is lower in the stack that the elements you want to prevent hover effects on), or specifically put in prevent default for onhover events for all elements in the stacking context except for the one you want to actually get a hover effect.

Related

How to use cursor style:ns-resize

Where can I use the cursor style: ns-resize?
Do I have to define an event[script] describing the functionality of the cursor. On what html objects can I use a cursor with this style?
This question is very important for how to use cursors with dragging functionality i.e. for the following cursor styles-
move
col-resize
row-resize
n-resize
s-resize
e-resize
etc.
The style of the cursor makes absolutely no difference whatsoever. You can put ns-resize on your entire document if you really want to, although I don't think your visitors will think much of your site if you do.
If you have an element for which you have programmed a resize function triggered by dragging something, then you may put the ns-resize cursor (or the appropriate one) on that handle to illustrate to the user that they can do that.

Prevent image from 'obscuring' onmouseover event below?

For a 'shooting gallery'-like game, there are images with an onMouseOver event that will show a crosshair (which follows the mouse) and an onMouseOut event that will hide it.
However, the instant the crosshair becomes visible, it covers the below image, activating its onMouseOut event which hides the crosshair.
This creates a 'flicker' effect which is very, very ugly.
Is there a way to prevent the crosshair image from obscuring the target below?
One easy solution is to create an onMouseOver for the crosshair that shows it (I know this is redundant, but it works for menus and the like).
Another solution would be to set a timeout in the onMouseOut to hide the crosshair. It will reduce the flickering and the crosshair will be visible out of the target for a short time.
Edit:
And another would be to perform a collision detection between the mouse and the elements, changing the mouseOver to a mouseMove in the target's parent element:
http://jsfiddle.net/sHecT/1/
The code is quite long, but its logic is what I've said above.
Just a note: The getElementsByClassName doesn't work in older browsers, but you can use an array of targets, as you create them, add them to an aray (probably you already has one) and use it in place of this call;
This one illustrates an easing function to position the crosshair smothly and the cursor is hidden when over the target
http://jsfiddle.net/sHecT/2/
Instead of using an image for your background, and an image for your cross-hairs, what if you used a div with a background image for your background instead, and then made the cross-hairs image a child of that div?
I haven't tested this, but since the cross-hair image would now be part of the content of the background div, I would imagine that it would no longer trigger a mouseout.
I believe The pointer-events property is exactly what you're looking for. It basically prevents an element from being the target of any sort of mouse-event so the elements underneath it can handle them instead. Parent elements can still react to the event.
HOWEVER it is only supported in the later versions of Firefox, Safari, and Chrome, and it probably won't be in the CSS specification until CSS4. It an awesome solution for supported browsers, but if you want to fix the issue in any version of IE or Opera you'll also need an alternate solution. I felt like it deserved a mention here though. :D

Get text behind an element

I am developing a magnifying glass and I was hoping I could get some help figuring out how I am going to do a step.
What I am doing is I have a div with a higher z-index than the content. It is moveable and draggable. It also has a transparent background so one can see the content (images & text) behind/underneath it that has a lesser z-index.
Now the part that I need help with is this:
I want to figure out exactly what content is behind the div (let's give it an ID of #glass).
Then my plan was to append a <span> before and a closing one after and style it with CSS3 scale transforms to increase the size so it acts as if it is magnified.
If you have a better idea on how to 'magnify' the content please share it.
So what I am looking to do in a spot of pseudo-code is:
Get position of #glass.
Get content behind #glass.
Store that in a variable or give it a class or something to refer it to.
Append a span before and after.
Style it with scale-transform.
Undo and reset the above when #glass moves.
I would really appreciate any and all help with any of these steps, but especially number 2 and 3, As I have no idea on how to do those.
You can listen for the mousemove event on every element in the page. each time the event fires you update a variable with the latest node being hovered over.
So as you are dragging around the glass, the mousemove event should be getting fired on the elements behind the glass (since you are hovering over them). And you can then use your latest node variable to get the element behind it.
Here a is Jsfiddle demonstrating how this could be done:
http://jsfiddle.net/wWVuy/

Handle mouse event on irregular shaped objects with event delegation

I need to handle mouse events on a page where there are multiple irregular-shaped objects (for example, houses) are stacked on top of each other. If I use the normal way of event delegation jQuery .on(), the event source reported will always be the top most object, even if user clicked on the transparent part of the object (or image).
Example: <img> tag that contains the red triangle will always be the event source even if I click at the X position.
I can detect that mouse click is not inside the triangle. What I need is a way to "forward" the event to the green triangle below.
EDIT: My current approach is to catch the events on a big div that wraps everything, then use jQuery selector and compare coordinates to find out which object is under the mouse, then check if the mouse is in transparent part or not. It works fine, but seems to be slow and consume a lot of memory, especially with mouse move events being fired continuously.
EDIT 2:
This image was extracted from Building a game engine with jQuery, and my approach was almost identical to that. And now, this is the question:
Are you drawing complex graphics using plain HTML elements? Not sure about your exact needs, but it might make more sense to use SVG or Canvas, where catching click events on shapes becomes much easier.

Simple JavaScript drag and drop witout the help of a library

I am simply looking for a way of using drag and drop without jquery or any other library. If a dragged object is dropped on another element the later element should start an event (in FF - better would be browser independent).
I know that drag and drop for JavaScript was discussed sometimes before but the previous postings didn't help me.
Although I found some examples it is not clear to me if there is a "drop" or "dragdrop" events exist but these things don't work:
<p ondrop='alert("It worked");'>Text</p>
<p ondragdrop='alert("It worked");'>Text</p>
How could this be done?
Many thanks in advance.
I agree with the other answers. A library will save you a lot of time and headache. This is coming from someone who just recently created a drag-and-drop control from scratch.
If you insist though this is what you'll need to do:
Bind a onmousedown event to the div you want to drag (div.onmousedown).
Change the div's position style to absolute (div.style.position = 'absolute')
Begin capturing mouse movement (document.onmousemove).
On mouse move update the div's position (div.style.top|left = '[location]px')
On the div's onmouseup event (or the document's) unbind all the handlers and do any other cleanup (null out position changes, etc).
Some problems a library will probably solve:
While dragging you will select text on the page (looks ugly).
Binding to events is different between browsers.
You have to calculate the size of the element being dragged if you want to show placeholders and to make it not "pop" when you begin dragging the control (since changing to absolute positioning will remove the element from flow).
You will probably want your dragged element to move fluidly so you will have to store some mouse offset when selecting the element or automatically center the element to the mouse.
If you want to drag an item in a list you'll have to write a ton more custom code for that list to accept the dragged item.
You'll have to take into consideration dragging when the window is scrolled and possibly dragging inside other elements that are positioned strangely.
I am simply looking for a way of using drag and drop without jquery or any other library.
I'm sorry, but there are no such thing as simply drag and drop without any library. You can write it all yourself, but that will be a lot of JS to make it work in all browsers.
Hmm. It's probably not that simple that you'd want to do it yourself, but I would look at Peter Michaux's FORK Javascript drag and drop library -- unlike JQuery or all those big libraries, FORK's modules are decoupled from each other, and are simple enough that you could probably look at Peter's source code and figure out the bits you need. (edit: I'd just use FORK.Drag as it's really small: 7.6KB total minified)
While I agree that library is the way to go, the answer you want is onmousedown, onmousemove, onmouseup. You have to handle those three events.
In onmousedown you'd find the target (event.target or similar in different browsers) and set draggedObject = event.target. You'd also start handling the onmousemove event.
Whenever the onmousemove event fired, you'd move the dragged element based on the difference in position since last time the onmousemove event fired.
In the onmouseup event, you'd clear your draggedObject variable and stop handling onmousemove.
It's not very crossbrowser, but it's the core of what you'd need to do for dragging and dropping.

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