Javascript image effects, fade-in

It's been a long while since my last post, but recently I found some time to write some new scripts. These are object oriented, so they are easier to use and have very little (or no) issues with scope collisions and the like. From now on, I will try to write all examples using OOP and 'classes'. This script is used to apply effects on pictures in a page. The effect shown in it is "Fade-in" - the image starts fully transparent and smoothly appears till it's fully visible. This is just the first effect of the series, and that is all I will show for today, but there will be additional effects added constantly :) Here's what I've made:

//THE object constructor (class, etc.)
function imageEffects(elmnt, pics, effectId, steps, time)
{
 //If the required parameters are not passed, show an error and stop.
 if(!elmnt || !pics)
 {
  alert('ERROR: imageEffects object not initialized properly!');
  
  return;
 } 
 
 //Assigning default values of the optional parameters
 if(!effectId)
  var effectId = 1;
 
 if(!steps)
  var steps = 50;
 
 if(!time)
  var time = 1000;
 
 
 this.elmnt = document.getElementById(elmnt); //html element (img) that will be manipulated
 this.pics = pics;          //an array with the pictures that will be shown
 this.steps = steps;         //number of steps for changing pictures
 this.effectId = effectId;       //id of the effect that will be applied. this is for future use
 this.effectTime = time;        //time that will be needed to change between pictures
 this.step = this.steps;        //used to control the smooth changing of the pictures
 this.pic = 0;           //current picture that is being shown
}


//Changes the opacity of any given element. cross browser.
imageEffects.prototype.setOpacity = function(opacity) 
{
   this.elmnt.opacity = (opacity / 100);
   this.elmnt.filter = "alpha(opacity="+opacity+")";
   this.elmnt.MozOpacity = (opacity / 100);
 this.elmnt.KhtmlOpacity = (opacity / 100);
}

//This prototype changes the pictures, handles steps, etc.
imageEffects.prototype.changePic = function(reverse)
{
 //If the previous picture hasn't finished showing, we need to wait
 if(this.step < this.steps)
  return;
 
 //If we got here, the previous picture has finished showing and the user now wants to change it. 
 //Set the step to 0 to start the effect again
 this.step = 0;
 
 if(reverse) //Show previous picture (or if this is the first one - show last)
 {
  if(this.pic == 0)
  {
   this.pic = this.pics.length-1;
  }
  else
   this.pic--;
 }
 else //Show next picture (or if this is the last one - show first)
 {
  if(this.pic == this.pics.length-1)
  {
   this.pic = 0;
  }
  else
   this.pic++;
 }
 
 
 //Change the image
 this.elmnt.src = this.pics[this.pic];
 
 //Determine the time interval that will be used based on the overal time and number of steps 
 var interval = this.effectTime/this.steps;
 
 for(i = 1; i < this.steps+1; i++)
 {
  //call the prototype that visualizes the effect
  setTimeout(methodize(this.setOpacity, this), i*interval);
 }
}


//The fade-in effect. Smoothly changes opacity of the picture from 0 to 100
imageEffects.prototype.setOpacity = function()
{
 //if we've reached the last step - stop the effect. Generally, this soudn't happen, cause it's 
 //controlled by the code that calls the effect, but it's an extra insurance. 
 if(this.step == this.steps)
    return;

 //Determine the opacity that the picture will have at this step.. 
 var opacity = this.step*(100/this.steps);

 //..and apply it to the image. 
 var element = this.elmnt.style; 
 
 element.opacity = (opacity / 100);
   element.filter = "alpha(opacity="+opacity+")";
   element.MozOpacity = (opacity / 100);
   element.KhtmlOpacity = (opacity / 100);
   
   //Go to the next step
   this.step++;
}

//This is a very simple, yet very powerful function that basically allows us to call objects from another 
//scope,in fact, any scope we want, which is not possible with a language construct or anything of the like..   
//There are still a lot of limitations in javascript and this is breaking one of them :)
//This is where I heard of it the first time I think - 
//http://www.tapper-ware.net/2006/12/object-oriented-programming-and-event.html. There are some additional 
//features in the example and I recomend you read it, but we just don't need them here. 
function methodize(methodize_func,methodize_scope)
{
    return (function() { methodize_func.call(methodize_scope); });
}

The html we need to use to get this working is just an image element and some kind of event trigger. We can use any of the event triggers that exist, but I think it's most appropriate to use either onclick or onmouseover. I've set an example page that shows three pictures. The first one is changed onclick. The second one is changed by clicking on the two arrows beneath it. The first arrow shows previous picture and the second one shows next. The last picture is changed onmouseover, and it changes in reverse/descending order. I've used a div and some other elements to position the elements on the page, but the code itself doesn't require anything else except an image. Here is the html:

<div style="width: 1024px; position: absolute; left:50%; margin-left: -512px; text-align: center">
<img id="img" src="1.jpg" style="width: 512px" onclick="test2.changePic(1);">
<br /><hr />
<img id="img2" src="2.jpg" style="width: 1024px"><br /><br />
<img id="l_arrow" class="arrow" src="lArrow.gif" onclick="test.changePic(1);">
     
<img id="r_arrow" class="arrow" src="rArrow.gif" onclick="test.changePic();">
<br /><hr />
<img id="img3" src="3.jpg" style="width: 1024px" onmouseover="test3.changePic();">
</div>

Now that we have the html, we need to create the imageEffects objects for every picture we want to manipulate. These are already used in the html and are named test, test2 and test3. Lets create the objects now:

//The first one will change the pictures for two seconds (2000 miliseconds)
//and will do it in 40 steps
var test = new imageEffects('img', new Array('1.jpg', '2.jpg', '3.jpg'), 1, 40,
2000);

//The second will use the default values for steps and time, which are -
//change the pictures for a second, in 50 steps.
//This one uses the same pictures, but in slightly different order.
var test2 = new imageEffects('img2', new Array('2.jpg', '3.jpg', '1.jpg'));

//The third one will change the pictures for 3 seconds in 100 steps
//This one uses the pictures in completely different order.
var test3 = new imageEffects('img3', new Array('3.jpg', '1.jpg', '2.jpg'), 1,
100, 3000);

This is pretty much it. I've put the code on one of my pages, so you can use it on your page using this code:

<script type="text/javascript" src="http://enikoloff.info/scripts/imageEffects.js"></script>

This will create the imageEffects class on your page. Then all you need to do is create some instances of that object (just as I did with test, test1 and test2) and call them with some event trigger. Don't forget to visit my site where you can find other examples on using this class and other free scripts :) P.S You can see the example from above here.

Javascript image magnifier

A friend of mine has asked me if she can put a script on her image gallery that magnifies the pictures the way that desktop software does when you zoom in. The main reason for this was that some of the people, browsing the gallery, have found it difficult to read some funny stuff like a road sign in the background of the picture. She needed something to work on the page itself, so the users won't need to save the picture on their pc and then zoom in to read this funny road sign. So, here it is, a javascript image magnifier:

I've made some settings for the the script to be more easily adjustable to what you need. The code starts with the declaration of the magnifier_settings array:

var magnifier_settings = new Array();
magnifier_settings['widht'] = 100;
magnifier_settings['height'] = 100;
magnifier_settings['zoom_level'] = 2;

The width and height indexes of the array are used to manage how big the magnifier should be. The zoom_level is, well, a zoom level :) The value in this var will be used to determine how much times the magnified image will be biger than the original one.

What fallows is a function that I've already posted about, which gets the offset coordinates of the cursor, according to the image on which it is called. This offsets will be used to determine where should the magnifier be displayed.

function get_image_offset(e, id)
{
 offset_x = e.offsetX ? e.offsetX : e.pageX-document.getElementById(id).offsetLeft;
 offset_y = e.offsetY ? e.offsetY : e.pageY-document.getElementById(id).offsetTop;
 
 magnify(document.getElementById(id));
}

The new addition to the code in this function is the call to magnify(), which is the function that does the magnification.

function magnify(elmnt)
{
 //check if the element exists; if it does not - create it
 if(!document.getElementById('magnifier'))
 {
  //create the div that will hold the magnifier
  var magnifier = document.createElement('div');
  magnifier.id = 'magnifier';
  magnifier.style.width = magnifier_settings['widht'];
  magnifier.style.height = magnifier_settings['height'];
  magnifier.style.overflow = 'hidden';
  magnifier.style.border = '2px solid #000';
  magnifier.style.position = 'relative';
  
  //magnified image. The original image is used to create the new one, which means that this function 
  //will work on any number of images on the same page, without the need to declare them or anything else..
  var magnifier_img = document.createElement('img');
  magnifier_img.id = 'magnifier_img';
  magnifier_img.src = elmnt.src;
  magnifier_img.width = parseInt(elmnt.width)*magnifier_settings['zoom_level'];
  magnifier_img.height = parseInt(elmnt.height)*magnifier_settings['zoom_level'];
 }
 else 
 {
  //if the element already existst we don't need to recreate it. Just declare the same variables, as used when creating the elements. 
  //This saves a lot of work for the browser and makes the script run smoother even on older PCs
  var magnifier = document.getElementById('magnifier');
  var magnifier_img = document.getElementById('magnifier_img');
 }
 
 //Adjust the magnifier position. Basically, it is set to the offset of the cursor plus a random value(i use 25) 
 //that will move the magnifier a little bit to the right  bottom of the page. This is used with two purposes: 
 //1. the magnifier will not pop over the cursor, so the user will actually see what will be magnified :)
 //2. this resolves an issue with the onmouseover trigger of the original image. If the value is not altered by 25, 
 //the instant when the magnifier is displayed, a onmouseout event is triggered on the original image, cause 
 //the mouse is now over the magnifier and not the original image. This causes the magnifier to be destoyed 
 //and in general is quite the oposite of what we want, cause this adds a big load to the client machine.
 //The top value is altered by the elements height, cause if the image is not at the top of the page,  
 //the magnifier will be misplaced somewhere above the image
 magnifier.style.left = offset_x+25;
 magnifier.style.top = offset_y+25-elmnt.height; 
 
 //Put negative margins to the magnified image, so the will show at the right place in the magnifier div
 magnifier_img.style.marginLeft = '-'+offset_x*magnifier_settings['zoom_level']+'px';
 magnifier_img.style.marginTop = '-'+offset_y*magnifier_settings['zoom_level']+'px';
 
 
 //Check again, if the magnifier is not created, cause if it's not we need to append it to the page elements
 if(!document.getElementById('magnifier'))
 {
  magnifier.appendChild(magnifier_img);
  
  //The only way I figured this magnification thing would work is using an image 'holder', which is a div 
  //with the same id as the  element plus the part '_holder'.
  var id = elmnt.id+'_holder';
  
  document.getElementById(id).appendChild(magnifier);
 }
}

//Removes the magnifier from tha page. This can be changed to just alter the magnifier's display property to 'none'
//or visibility to 'hidden', but i figured removing it is the most appropriate way
function hide_magnifier(id)
{
 id += '_holder';
 
 if(document.getElementById('magnifier'))
  document.getElementById(id).removeChild(document.getElementById('magnifier'));

}

And now, the HTML code that will display the images on the page:

<div id='test_holder'>
<img id='test' src='test.jpg' onmousemove='get_image_offset(event, this.id);' onmouseout='hide_magnifier(this.id)'>
</div>
<div id='test2_holder'>
<img id='test2' src='test2.jpg' onmousemove='get_image_offset(event, this.id);' onmouseout='hide_magnifier(this.id)'>
</div>
<div id='test3_holder'>
<img id='test3' src='test.jpg' onmousemove='get_image_offset(event, this.id);' onmouseout='hide_magnifier(this.id)'>
</div>

You can put as many images as you wish, they will be handled by the same function automatically. I've used 3 images to show how the script works on more that one image. You can put the code on you entire gallery or just a single image, it's your call :)

The two things required for this script to work are as fallows:

• You need to have an id on each image. This is very important, cause otherwise the script won't work and a handful of javascript errors will occur when the user mouseover's an image that doesn't have an 'id' property. You can use whatever id you want, just use one :)
• The second thing is a div that holds the images. This is also very important, cause the script again won't work, and again there will be many many javascript errors when you mouseover the images. The requirement here is that the id for the div is the same as the id of the image it holds, plus the text '_holder'. You can use whatever styles you want on that div. If you want to, you can also put some other stuff in it, not just the image. Again - just put the images in divs and use the same ids with the text '_holder' added to them.

I made two demos for this script with different settings. The first one is here and it uses a 100x100 pixels magnifier, with a zoom level of 2. You can download the code from here. The second one can be seen here and it uses 200x200 pixels magnifier with the zoom level of 4. You can download this code from here.

Javascript image map

Have you ever needed to know exactly where the user has pointed or clicked on an image? Well, this is easily done with HTML image maps, they are quite useful. But they do have some disadvantages. Using an HTML/XHTML image map requires form submission or page redirection to be used. What if you need to display appropriate content somewhere on the page, depending on where the user has pointed? Here is a way to get the offset coordinates of the pointer, inside an image.

function get_image_offset(e, id)
{
offset_x = e.offsetX ? e.offsetX : e.pageX-document.getElementById(id).offsetLeft;
offset_y = e.offsetY ? e.offsetY : e.pageY-document.getElementById(id).offsetTop;
 
document.getElementById('x').innerHTML = offset_x;
document.getElementById('y').innerHTML = offset_y;
}

This function takes two parameters - the event (mouseover, click, mousemove), and the id of the element (image) that we wan't to use. It saves the offset in offset_x and offset_y. If client's browser is IE, the offsetX and offsetY values will be used, but since this is not supported by the other browsers, we can use the pageX and pageY values and the elements offsetLeft and offsetTop values to determine the cursor offset.

After the two lines of code have been executed we have the offset in the variables offset_x and offset_y and we can use them for any purpose. I have added two span elements to the HTML, which show the offset as the user moves the mouse over the image. Here is the rest of the code you need to get this working:

<img id='my_image_map' src='test.jpg' onmousemove='get_image_offset(event, this.id)'>
<br />
X: <span id='x'>0</span>; Y: <span id='y'>0</span>

Now, presuming you have a 'test.jpg' file inside the folder of your page, you will see that when you move the mouse over it, the values of the two spans change width the coordinates of the cursor offset. You can change the code that alters the innerHTML of the two spans and do whatever you need to do with this offset coordinates. You can also change the event that triggers the function. I use onmousemove to update the coordinates every time the cursor moves over the image, but you can use other triggers like onclick, ondblclick, etc.

P.S. You can see a demo of this code here and you can get the example code from here