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Setting a JavaScript timer

From: Create Animated Rollovers with jQuery and Dreamweaver

Video: Setting a JavaScript timer

Now in order to create the illusion that the thumbnail graphics are actually animating in the background we're going to need to set up a JavaScript timer, and then we're going to need to take those large thumbnails that we created and ship those back and forth. So in looking at our sketch here what we're going to be doing is taking those large graphics and moving them 200 pixels at a time which is going to match exactly the width of the thumbnail area we created in CSS and match those up with the width of the individual clipping areas we made inside of our Photoshop file. When we get to the very last item we'll do a check inside of jQuery to see what the negative position of that background graphic is.

Setting a JavaScript timer

Now in order to create the illusion that the thumbnail graphics are actually animating in the background we're going to need to set up a JavaScript timer, and then we're going to need to take those large thumbnails that we created and ship those back and forth. So in looking at our sketch here what we're going to be doing is taking those large graphics and moving them 200 pixels at a time which is going to match exactly the width of the thumbnail area we created in CSS and match those up with the width of the individual clipping areas we made inside of our Photoshop file. When we get to the very last item we'll do a check inside of jQuery to see what the negative position of that background graphic is.

When it equals the end of the item, we're going to switch it back to the beginning and just let them run in a loop. So now back in Dreamweaver what we're going to do inside of the index.html file, I first want to set up a debugging area so that we can send the value of the position to our HTML page and be able to see that the counter is working and tell where the thumbnails are being positioned. So inside of the index.html file we're going to click on Source Code, and then we're going to go to Code view. In inside of the HTML file before the comment that says Hidden DIV container goes here, let's hit a Return, I start by typing a paragraph tag and ending that.

Inside of there, we're going to type the word test. Inside of the p tag we're going to add a class = "debug" style = "color":#fff;. Let's switch back to Design view. So now this area here is what we're going to use to make sure the timer is working.

Let's come up to video_ gallery.js, the related file. Let's click on Code view. What we're going to do inside of here before the (document).ready, let's set up two items. First we're going to set up a variable. We're going to call this thumbnailPosition, we're going to set that = 0. Next we're going to type function.

We're going to name this animateThumbnail, that's going to be a new custom function we're creating, beginning and ending parenthesis, beginning and ending bracket. Let's put that open on the bracket. Inside of this function we're going to type var newPosition = window.thumbnailPosition. Then we're going to use an asterisk to multiply this * -1.

What that's going to do is give us a negative number, because what we need to do is set the X position of the CSS to a negative number so it moves to the left. On the next line we're going to update that debugging area we created. So we are going to type $('p.debug').html();. Let's come up here and copy the variable name newPosition and let's paste it inside of the parentheses inside of the HTML.

So whatever value comes out from thumbnailPosition, which is the variable set up here, *-1, that's going to be the new value in that paragraph tag with the debug class. So now we have this animateThumbnail function we've created inside of the (document).ready. So once jQuery loads the whole page and the document is ready for functions to begin we're going to set a standard JavaScript timer called setInterval(animateThumbnail,500);.

So what this is means is the setInterval is going to run the animateThumbnail function twice a second. So it's going to come up here, set the newPosition, and update the debug area two times for every second. Now that we have our thumbnail variable set and we have our animateThumbnail function set and we have a setInterval that's running that function twice every second, in the next movie we'll set up a conditional statement inside of the animateThumbnail that will make sure that the icon position never goes wider than the actual width we set inside of Photoshop.

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