Image cutting plug-in based on jQuery_jquery

Step 1: Establish a workspace

First, we need to create a workspace for our tutorial, establish the file hierarchy as shown in the figure, and create a corresponding empty file.

< ;title>




< ;/head>

Jquery Image Croping plug-in

width="480" />

[/code]
style.css

Copy code The code is as follows:

* {
margin : 0;
outline : 0;
padding : 0;
}
/*Initialize web page style*/
body {
background-color : #ededed;
color : #646464;
font-family : 'Verdana', 'Geneva', sans-serif;
font-size : 12px;
text-shadow : 0 1px 0 #ffffff;
}
h1 {
font-size : 24px;
font-weight : normal;
margin : 0 0 10px 0;
}
div#wrapper {
margin : 25px 25px 25px 25px;
}
/*Select the div with the id of wrapper*/
div.image-decorator {
-moz-border-radius : 5px 5px 5px 5px;/*Sharpening of boxes for Firefox browsers* /
-moz-box-shadow : 0 0 6px #c8c8c8;/*Border shadow processing of the box for Firefox browser*/
-webkit-border-radius : 5px 5px 5px 5px;/*WebKit Is an open source browser engine*/
-webkit-box-shadow : 0 0 6px #c8c8c8;
background-color : #ffffff;
border : 1px solid #c8c8c8;
border- radius : 5px 5px 5px 5px;
box-shadow : 0 0 6px #c8c8c8;
display : inline-block; /* Render the object as an inline object, but render the object's content as a block object. Adjacent inline objects will be rendered on the same line, allowing spaces. Supported browsers are: Opera, Safari*/
height : 360px;
padding : 5px 5px 5px 5px;
width : 480px;
}

The above we By changing the background color and setting some basic styles, we can make our page more readable.
Step 3: Write a basic jQuery plug-in
Let’s start writing a basic jQuery plug-in. Before writing, if you, the reader, have never had the experience of writing a jQuery plug-in, it is recommended to read the official instructions first. Plug-in tutorial (http://docs.jquery.com/Plugins/Authoring), this is the English version, the Chinese version is not found, the author plans to translate it, so stay tuned.
Open /resources/js/imageCrop/jquery.imagecrop.js and add the js code as shown below

Copy the code The code is as follows:

//Generally, please include the plug-in code you write in '(function($) { // Plug-in code here}) (jQuery);'
(function($) {
$.imageCrop = function(object, customOptions) {};
$.fn.imageCrop = function (customOptions) {
//Iterate over each object
/ /Iterate over each object
this.each(function () {
var currentObject = this,
image = new Image();
//When the object is loaded, append ImageCrop cutting function
image.onload = function () {
$.imageCrop(currentObject, customOptions);
};
//Reset the address of the image because sometimes the image is cached Cannot be loaded quickly
image.src = currentObject.src;
});
//Unless your plug-in returns a certain value, the function is usually required to return the 'this' keyword
//This is used to keep programming chained
return this;
};
}) (jQuery);

We have just extended jQuery by adding a new method attribute on the jQuery.fn object. Now we have a basic plugin that iterates over each object and attaches the imageCrop function to it when it's loaded. Noticed that the cached image might not be downloaded quickly, so reset its image address.

Step 4: Add customizable options

With customizable options, users will have more choices and the plug-in will be more flexible. (Note: The following codes are in order)

Copy the code The code is as follows:

/ / Encapsulating the plugin's options in a constant object is far better than passing a long list of parameters to pass.
//This allows expansion by default in the plug-in
var defaultOptions = {
allowMove: true,
allowResize: true,
allowSelect: true,
minSelect: [ 0, 0],
outlineOpacity: 0.5,
overlayOpacity: 0.5,
selectionPosition: [0, 0],
selectionWidth: 0,
selectionHeight: 0
};

// Set the options as default options
var options = defaultOptions;

// Then merge it with the customer-customized options
setOptions(customOptions);

Above we define an array containing default options, and then use the setOption function to merge the default options and customized options. Now let us write the merge function body

Copy the code The code is as follows:

// Will Default options and customer-customized options are merged
function setOptions(customOptions) {
options = $.extend(options, customOptions);
};

$.extend() The function implements the function of merging two or more objects into the first object.

Options

The following list explains each option in the plugin

allowMove – Specifies whether the selection can be moved (the default value is true.)
allowResize – Specifies whether the selection area can be resized (the default value is true)
allowSelect – Specifies whether the user can resize the selection area (the default value is true)
minSelect – The minimum size of a new selection area (The default size is [0, 0])
outlineOpacity – the transparency of the outline (the default value is 0.5)
overlayOpacity – the transparency of the overlay (the default value is 0.5)
selectionPosition – the selection area Position (default is [0, 0])
selectionWidth – the width of the selection area (the default value is 0)
selectionHeight – the length of the selection area (the default value is 0)
Step 5: Create an image layer

In this step we will change the structure of the document to prepare for the next step: the surface of the plug-in

First we need to initialize the image layer, and then initialize the image containing layer

Copy code The code is as follows :

// Initialize the image layer
var $image = $(object);

// Initialize an image support layer
var $holder = $('

')
.css({
position: 'relative'
})
.width($image.width())
.height($image. height());

// imag is included in the holder layer. wrap() function

$image.wrap($holder)
.css({
position: 'absolute'
});

As you can see, the containing layer and the image have the same size and are positioned relative to each other. Then we use the .wrap function to make the image contained within it

On top of the image is the overlay:

Copy code The code is as follows:

//Initialize an overlay and place it on top of the image
var $overlay = $('

')
.css({
opacity: options.overlayOpacity,
position: 'absolute'
})
.width($image.width())
.height($image.height())
.insertAfter($image);

This layer is also the same size as the image, but is absolutely positioned. We get transparency from options.outlineOpacity. This element has an Id, so we can change its style by changing the css via the plugin. At the end we use the .insertAfter($image) method to place the overlay just below the image layer.

The lower layer is the trigger layer

Copy the code The code is as follows:

//Initialize a trigger layer and place it on top of the overlay
var $trigger = $('

')
.css({
backgroundColor: '#000000',
opacity: 0,
position: 'absolute'
})
.width($image.width())
.height($image. height())
.insertAfter($overlay);

This time it will not be visible to the user, but it will handle some events.

Next is the border layer and selection layer

Copy the code The code is as follows:

//Initialize a border layer and place it on top of the trigger layer
var $outline = $('

')
.css ({
opacity: options.outlineOpacity,
position: 'absolute'
})
.insertAfter($trigger);

// Initialize a selection layer and set it Above the border layer
var $selection = $('

')
.css({
background: 'url(' $image.attr('src') ') no-repeat',
position: 'absolute'
})
.insertAfter($outline);

　.attr() method is used to return a specific The value of the attribute, we use it to get the address of the image and use it as the background of the selection layer

Absolute positioning inside relative positioning

A relatively positioned element can control an absolutely positioned element , so that the absolutely positioned element is inside the relatively positioned element. This is also why the containing layer is relatively positioned, and all its child elements are absolutely positioned

Step 6: Update the interface

　　　First we need to initialize some global variables

Copy code The code is as follows:

//Initialize global variables
var selectionExists,
selectionOffset = [0, 0],
selectionOrigin = [0, 0];

selectionExists will tell us whether there is a selection area, selectionOffset will contain the offset relative to the starting point, selectionOrigin Will contain the starting point of the selection area

The following condition is used for the selection area to exist when the plugin is loaded

Copy code The code is as follows:

//Indicates whether the size of the selection area is larger than the smallest, and then sets whether the selection area exists based on it
if (options.selectionWidth > options. minSelect[0] &&
options.selectionHeight > options.minSelect[1])
selectionExists = true;
else
selectionExists = false;
Now we will call updateInterface to initialize the plug-in. Interface

//Call the 'uploadInterface' function for the first time to initialize the plug-in interface
updateInterface();