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What we are going to do now is take what we have learned about events and the previous chapters and we are going to build a pretty sophisticated effect. And what we are going to do is build an image rotator that has a nice fading effect in it. So before I show you the code, let me bring up the finished image rotator in the browser. So if you look in the Exercise Files folder under the Effects chapter, you will a couple of files. There is the imagerotator_ start and imagerotator_finished. So let me just bring this up in the browser.
You can see that what's happening is over a couple of seconds, we have a nice little image slideshow where the images are fading from one to the next and they are just doing this in a circular pattern. So there are four images and each one is fading on top of the next. Let me bring this up in Firefox too, so you can see that it works there. Let's bring up in Firefox browser. Same idea. So you can see that it's slowly fading across the images.
So here is the images that we are going to rotate. So a couple of things. First, everything is contained inside a parent div and the parent div I have got here is named photoShow and then I have got four divs inside that. Each one of those divs contains an image. The first div has a class applied to it named Current. So you can see that inside each one of these divs there is an image pointing to a path and each one has a height and a width.
What I have done here is define these four images and let's take a look at the styles applied to each. The photoShow div itself has a height and a width applied and that matches the height and width of the images that I am rotating. Then the divs inside the parent div are positioned absolutely. So that's causing all the images to stack up underneath each other. By default, I am giving each image a z-index of 0. So they're going to be underneath at the bottom of the stack. Then I have got two other style sheets, one called Previous and one called Current.
The Current style sheet basically has a z-index of 2. So whichever div has that Style Sheet applied is going to be the one that is on top of all the other images, and you can see that that's this div, and that image is inside the div. So this one will be on the top of everybody else. Then we have another Style Sheet named Previous and that has a z-index of 1. So whichever div has this Style Sheet will be directly under this guy right here. Now, that's not initially assigned. We are going to assign that dynamically as part of the rotation effect.
So now that we have got all the contents set up, let's take a look at the code. So I have got my jQuery Library included, and what I need to do now is write the code that sets up the image rotator. So what I am going to do is write a function that executes when the page gets loaded. This is the jQuery document ready event and what I am going to do is call setInterval on a function I am going to write called rotateImages and I am going to have that run every two seconds, so 2000 milliseconds.
Okay, so now, I need to write the function to rotate the images. There are a couple of things we need to do. What we are going to do is figure out which photo is the current one and which photo is the next one. What we are going to do is take whatever the current photo on top is. We are going to move it underneath the photo that comes next. So that's going to be the image that fades up. So we are going to move the current photo underneath the next one, set the next photo's Opacity to 0, and then have it fade up in front of the photo that's in front of it.
So I am going to have a variable here named oCurPhoto and I am going to use jQuery to get a reference to whichever photo is current. So what I am going to do is look for inside the photoShow div, I am going to look for whatever div has the current Style Sheet applied to it, because that's the current photo. Then I am going to look for the next photo and again I am going to use jQuery for that.
So to get the next photo, recall from our selector and retrieving content section that there is a function called Next. So I am going to say oCurPhoto.next. This will get the next sibling after wherever this current div is here. So if this div is current, then the next div is this guy and if this div is current, then this is the next guy. If this div is current, there is no next. You can see that we are at the end of the div list. We have to handle that condition. So if that's the case, then the jQuery result that comes back from the next function will be of length 0.
We can check that condition. So we say if oNxtPhoto.length, in other words, there is nothing in the jQuery result set, is equal to 0, then what we need to do is go back to the top of the loop. And to do that, remember using jQuery, we are going to say well oNxtPhoto = and what we are going to do is simply get the first div that's inside the photoShow parent div, which will be this guy right here.
So that's how we are going to get the looping behavior. So now we've figured out which div is current and which one is next, we need to do the CSS animation that causes the Opacity to animate. So what we are going to do is tell the current photo to remove the class that is current, because it's no longer the current photo, and we are going to add the previous class. What's going to happen now is the Current class is going to come off, Previous is going to go on, so it's going to drop down one order in the z-index.
We are going to tell the Next Photo that we are going to set its CSS property, and make its Opacity 0, because that's what we are going to animate up. The div will start out invisible. Then we are going to set the Next Photo to be the current photo. So now this guy is going to move on top and remember he is invisible. So his Opacity is 0, he is now on top. But now we need to animate it up from Opacity 0 to Opacity 1.0.
So it will fade up in front of the image that's behind it. So we will write Animate, and we are going to write a Custom Animation function here. The Animation function will simply animate the Opacity up to 1.0 over a duration of 1 second, and then we are going to have a Call Back function. The Call Back function will simply tell the current photo to remove its previous class.
So now, there is no more class set on it. It's back at the bottom of the stack along with the other photos. So that is pretty much all we need to do. So just a quick review. We've found out which photo is current, we get the one that's next in line. If we are at the end of the list, we move back to the beginning. Whichever photo is current, we remove the current class and make it drop down in the z-index. Then we take whatever is next, set it to be invisible, and make it on top.
Now that it's on top, all we have to do is animate the Opacity up to fully visible over a second, so it will appear to fade up in front of the image that it's in front of and then we tell the photo that was directly behind the next photo to drop down at the bottom of the z-index. Since we are calling set interval, this function will be called every two seconds. So this will happen over and over and over again. So let's save and what we are going to do now is go back out to the browser. So let's bring up the imagerotator_ start in the browser, and you can see that every two seconds, we are just changing which photo is on top and animating the Opacity up.
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