概述：
在WebGIS开发中，经常会有用户提需求，要实现卷帘功能，卷帘功能主要是实现两张图之间的对比。在前文中，讲到了openlayers3以及Arcgis for js中卷帘的实现，在本文讲述如何在openlayers2中实现卷帘功能。
结果展示：
实现代码：
在此，扩展了一个名为Swipe的Control，Swipe的代码如下：
/*
*
* @requires OpenLayers/Control.js
*/
/* The following globals are for JSLint */
/* jslint browser: true, vars: true */
/* global OpenLayers, escape */
/** api: (define)
* module = OpenLayers.Control
* class = Swipe
* base_link = `OpenLayers.Control <http://dev.openlayers.org/apidocs/files/OpenLayers/Control-js.html>`_
*/
/** api: example
* Sample code to add a swipe control
*
* .. code-block:: javascript
*
* var map = new new OpenLayers.Map("mymap");
* var Swipe = new OpenLayers.Control.Swipe({map: map});
* map.addControls([swipe]);
* Swipe.activate();
*
*/
/** api: constructor
* .. class:: Swipe(options)
*
* :param options: ``Object`` options
*
* :return: ``OpenLayers.Control.Swipe``
*
* Add a swipe control in the map
*/
OpenLayers.Control.Swipe = OpenLayers.Class(OpenLayers.Control, {
/** api: config[map]
* ``OpenLayers.Map``
* A `OpenLayers.Map <http://dev.openlayers.org/docs/files/OpenLayers/Map-js.html>`_ instance
*/
map: null,
32,
/** api: config[swipeRatio]
* ``Number``
* A number between 0 and 1 defining the position of the swipe relative to the map (from right to left)
*/
swipeRatio: null,
swipeLayer: null,
isTitleVisible: false,
isDragging: false,
mouseDragStart: null,
/**
* Property: divEvents
* {<OpenLayers.Events>}
*/
divEvents: null,
initialize: function (options) {
"use strict";
OpenLayers.Control.prototype.initialize.apply(
this,
arguments
);
// Manage position of swipe
if (this.map && this.map.swipeRatio) {
// Swipe ratio can be set in the map (in order to manage permalink)
this.setSwipeRatio(this.map.swipeRatio);
} else {
if (!this.swipeRatio) {
// Default swipe ratio is 0.5
this.setSwipeRatio(0.5);
} else {
// Swipe ratio can be set to the control
this.setSwipeRatio(this.swipeRatio);
}
}
},
/**
* Method: activate
* Activates the control.
*
* Returns:
* {Boolean} The control was effectively activated.
*/
activate: function () {
this.map.swipeActive = true;
this.map.events.triggerEvent("changelayer", {
layer: this.swipeLayer,
property: "name"
});
OpenLayers.Control.prototype.activate.apply(this, arguments);
this.map.events.on({
"addlayer": this.handleAddLayer,
"removelayer": this.handleRemoveLayer,
"changelayer": this.handleChangeLayer,
"updatesize": this.handleUpdateSize,
"move": this.handleMove,
"scope": this
});
if (this.isLayersInLayerSwitcher()) {
this.div.style.display = 'block';
this.viewBigArrow();
}
this.resize();
return true;
},
/**
* Method: deactivate
* Deactivates the control.
*
* Returns:
* {Boolean} The control was effectively deactivated.
*/
deactivate: function () {
this.map.swipeActive = false;
this.map.events.triggerEvent("changelayer", {
layer: this.swipeLayer,
property: "name"
});
this.map.events.un({
"addlayer": this.handleAddLayer,
"removelayer": this.handleRemoveLayer,
"changelayer": this.handleChangeLayer,
"updatesize": this.handleUpdateSize,
"move": this.handleMove,
"scope": this
});
this.hideBigArrow();
this.hideLayerTitle();
this.div.style.display = 'none';
if (this.swipeLayer) {
if (this.swipeLayer.layers) {
for (var i = this.swipeLayer.layers.length - 1; i >= 0; i--) {
var layer = this.swipeLayer.layers[i];
if (layer.div) {
layer.div.style.clip = 'auto';
}
}
} else {
this.swipeLayer.div.style.clip = 'auto';
}
this.swipeLayer = null;
}
return OpenLayers.Control.prototype.deactivate.apply(
this, arguments
);
},
/**
* Method: destroy
* Destroy control.
*/
destroy: function() {
this.map.events.un({
"addlayer": this.handleAddLayer,
"removelayer": this.handleRemoveLayer,
"changelayer": this.handleChangeLayer,
"updatesize": this.handleUpdateSize,
"scope": this
});
OpenLayers.Control.prototype.destroy.apply(this, arguments);
},
/**
* Method: draw
* Initialize control.
*
* Returns:
* {DOMElement} A reference to the DIV DOMElement containing the control
*/
draw: function() {
OpenLayers.Control.prototype.draw.apply(this, arguments);
this.elementLayer = document.createElement("div");
this.div.appendChild(this.elementLayer);
OpenLayers.Element.addClass(
this.elementLayer,
'olControlSwipeLayerHide'
);
this.elementLayerSpan = document.createElement("span");
this.div.appendChild(this.elementLayerSpan);
OpenLayers.Element.addClass(
this.elementLayerSpan,
'olControlSwipeLayerSpan'
);
this.elementLeft = document.createElement("div");
this.div.appendChild(this.elementLeft);
OpenLayers.Element.addClass(
this.elementLeft,
'olControlArrowLeft'
);
this.elementRight = document.createElement("div");
this.div.appendChild(this.elementRight);
OpenLayers.Element.addClass(
this.elementRight,
'olControlArrowRight'
);
OpenLayers.Control.prototype.draw.apply(this, arguments);
this.divEvents = new OpenLayers.Events(this, this.div, null, true, {includeXY: true});
this.divEvents.on({
"touchstart": this.divDown,
"touchmove": this.divDrag,
"touchend": this.divUp,
"mousedown": this.divDown,
"mousemove": this.divDrag,
"mouseup": this.divUp,
"mouseover": this.divMouseOver,
"mouseout": this.divMouseOut,
scope: this
});
return this.div;
},
/*
* Method: divMouseOver
* event listener for onmouseover event
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
divMouseOver: function(ev) {
OpenLayers.Element.addClass(
this.div,
'olControlSwipeHover'
);
//this.viewLayerTitle();
},
hideBigArrow: function() {
if (!this.isDragging) {
this.elementLeft.style.display = "none";
this.elementRight.style.display = "none";
}
},
viewBigArrow: function() {
if (!this.isDragging) {
this.elementLeft.style.display = "block";
this.elementRight.style.display = "block";
}
},
/*
* Method: divMouseOut
* event listener for onmouseout event
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
divMouseOut: function(ev) {
OpenLayers.Element.removeClass(
this.div,
'olControlSwipeHover'
);
this.hideLayerTitle();
this.viewBigArrow();
},
/**
* Method: passEventToDiv
* This function is used to pass events that happen on the map,
* through to the div, which then does its moving thing.
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
passEventToDiv:function(evt) {
this.divEvents.handleBrowserEvent(evt);
},
/*
* Method: divDown
* event listener for clicks on the div
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
divDown:function(evt) {
if (!OpenLayers.Event.isLeftClick(evt) && !OpenLayers.Event.isSingleTouch(evt)) {
return;
}
this.map.events.on({
"touchmove": this.passEventToDiv,
"mousemove": this.passEventToDiv,
"mouseup": this.passEventToDiv,
scope: this
});
this.mouseDragStart = evt.xy.clone();
OpenLayers.Event.stop(evt);
//this.viewLayerTitle();
this.hideBigArrow();
this.isDragging = true;
return false;
},
/*
* Method: divDrag
* This is what happens when a click has occurred, and the client is
* dragging. Here we must ensure that the div doesn't go beyond the
* bottom/top of the zoombar div, as well as moving the div to its new
* visual location
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
divDrag:function(evt) {
if (this.mouseDragStart && this.isDragging) {
var deltaX = this.mouseDragStart.x - evt.xy.x;
var left = parseInt(this.div.style.left, 10);
if ((left - deltaX) >= 0 &&
(left - deltaX) <= (this.map.size.w - this.width)) {
var delta = 0;
if (OpenLayers.BROWSER_NAME === "msie" || OpenLayers.BROWSER_NAME === "safari") {
delta = -1;
}
this.setSwipeRatio((left - deltaX) / (this.map.size.w - this.width + delta));
this.moveTo(this.computePosition());
this.clipFirstLayer();
this.mouseDragStart = evt.xy.clone();
}
OpenLayers.Event.stop(evt);
}
return false;
},
/*
* Method: divUp
* Perform cleanup when a mouseup event is received
*
* Parameters:
* evt - {<OpenLayers.Event>}
*/
divUp:function(evt) {
this.map.events.un({
"touchmove": this.passEventToDiv,
"mousemove": this.passEventToDiv,
"mouseup": this.passEventToDiv,
scope: this
});
if (!OpenLayers.Event.isLeftClick(evt) && evt.type !== "touchend") {
return;
}
if (this.mouseDragStart) {
this.mouseDragStart = null;
}
this.isDragging = false;
this.viewBigArrow();
if (evt.type === "touchend") {
this.hideLayerTitle();
}
OpenLayers.Event.stop(evt);
return false;
},
/*
* Method: clipFirstLayer
* Clip the first layer present in the layer switcher
*/
clipFirstLayer: function() {
var newFirstLayer = this.getFirstLayerInLayerSwitcher();
if (this.swipeLayer) {
if (newFirstLayer.id !== this.swipeLayer.id) {
if (this.swipeLayer.layers) {
for (var i = this.swipeLayer.layers.length - 1; i >= 0; i--) {
var layer = this.swipeLayer.layers[i];
if (layer.div) {
layer.div.style.clip = 'auto';
}
}
} else {
this.swipeLayer.div.style.clip = 'auto';
}
}
}
if (newFirstLayer) {
var width = this.map.getCurrentSize().w;
var height = this.map.getCurrentSize().h;
// slider position in pixels
var s = parseInt(width * this.getSwipeRatio() * ((this.map.getCurrentSize().w - this.width) / this.map.getCurrentSize().w), 10);
// cliping rectangle
var top = -this.map.layerContainerOriginPx.y;
var bottom = top + height;
var left = -this.map.layerContainerOriginPx.x;
var right = left + s + Math.ceil((this.width - 1) / 2);
//Syntax for clip "rect(top,right,bottom,left)"
var clip = "rect(" + top + "px " + right + "px " + bottom + "px " + left + "px)";
this.swipeLayer = newFirstLayer;
if (this.swipeLayer.layers) {
for (var i = this.swipeLayer.layers.length - 1; i >= 0; i--) {
var layer = this.swipeLayer.layers[i];
if (layer.div) {
layer.div.style.clip = clip;
}
}
} else {
this.swipeLayer.div.style.clip = clip;
}
}
},
/*
* Method: handleAddLayer
* Triggered when a new layer is added
*
* Parameters:
* object - {<OpenLayers.Event>}
*/
handleAddLayer: function (object) {
if (this.isLayersInLayerSwitcher()) {
this.div.style.display = 'block';
this.moveTo(this.computePosition());
this.clipFirstLayer();
} else {
this.div.style.display = 'none';
this.swipeLayer = null;
}
},
viewLayerTitle: function() {
if (!this.isTitleVisible && !this.isDragging) {
if (this.swipeLayer) {
var content = " " + this.swipeLayer.name;
this.elementLayer.innerHTML = content;
this.elementLayerSpan.innerHTML = content;
OpenLayers.Element.addClass(
this.elementLayer,
'olControlSwipeLayerView'
);
OpenLayers.Element.removeClass(
this.elementLayer,
'olControlSwipeLayerHide'
);
var width = parseInt(this.elementLayerSpan.offsetWidth) + 5;
this.elementLayer.style.width = width + "px";
this.elementLayer.style.marginLeft = "-" + width + "px";
}
}
this.isTitleVisible = true;
},
hideLayerTitle: function() {
if (!this.isDragging) {
this.elementLayer.innerHTML = '';
this.isTitleVisible = false;
OpenLayers.Element.addClass(
this.elementLayer,
'olControlSwipeLayerHide'
);
OpenLayers.Element.removeClass(
this.elementLayer,
'olControlSwipeLayerView'
);
}
},
/*
* Method: handleRemoveLayer
* Triggered when a new layer is removed
*
* Parameters:
* object - {<OpenLayers.Event>}
*/
handleRemoveLayer: function (object) {
if (this.isLayersInLayerSwitcher()) {
this.div.style.display = 'block';
this.moveTo(this.computePosition());
this.clipFirstLayer();
} else {
this.div.style.display = 'none';
this.swipeLayer = null;
}
},
/*
* Method: handleChangeLayer
* Triggered when the layer order is changed
*
* Parameters:
* object - {<OpenLayers.Event>}
*/
handleChangeLayer: function (object) {
if (object.property === 'order') {
if (this.isLayersInLayerSwitcher()) {
this.div.style.display = 'block';
this.moveTo(this.computePosition());
this.clipFirstLayer();
} else {
this.div.style.display = 'none';
this.swipeLayer = null;
}
}
},
/*
* Method: handleUpdateSize
* Triggered when the map size changed. In this case the swipe control is updated accordingly.
*
* Parameters:
* object - {<OpenLayers.Event>}
*/
handleUpdateSize: function (object) {
//we have to delay this on Android devices
if (navigator.userAgent.toLowerCase().indexOf("android") > 0) {
var self = this;
setTimeout(function() {
self.resize();
}, 10);
} else {
this.resize();
}
},
/*
* Method: handleMove
* Triggered when the map is moved. In this case, the clip ares has to be updated
*
* Parameters:
* object - {<OpenLayers.Event>}
*/
handleMove: function (object) {
this.clipFirstLayer();
},
/*
* Method: resize
* Resize the swipe and update the first layer clipping
*/
resize: function() {
this.div.style.height = this.map.getCurrentSize().h + 'px';
this.div.style.width = this.width + 'px';
this.moveTo(this.computePosition());
this.clipFirstLayer();
var topPosition = (this.map.getCurrentSize().h / 2) - 32;
this.elementLeft.style.marginTop = topPosition + 'px';
this.elementRight.style.marginTop = topPosition + 'px';
},
/*
* Method: computePosition
* Recompute the position of the swipe acording to swipeRatio and the size of the map
*/
computePosition: function() {
var y = 0;
var x = this.getSwipeRatio() * (this.map.size.w - this.width);
return new OpenLayers.Pixel(x, y);
},
/*
* Method: getFirstLayerInLayerSwitcher
* Get the first layer visible in the layer switcher
*/
getFirstLayerInLayerSwitcher: function() {
for (var i = this.map.layers.length - 1; i >= 0; i--) {
var layer = this.map.layers[i];
if (layer.displayInLayerSwitcher) {
return layer;
}
}
return null;
},
/*
* Method: isLayersInLayerSwitcher
* Check the presence of a layer in the layer switcher
*/
isLayersInLayerSwitcher: function() {
for (var i = 0, len = this.map.layers.length; i < len; i++) {
var layer = this.map.layers[i];
if (layer.displayInLayerSwitcher) {
return true;
}
}
return false;
},
setSwipeRatio: function(ratio) {
this.map.events.triggerEvent("changelayer", {
layer: this.swipeLayer,
property: "name"
});
this.map.swipeRatio = ratio;
this.map.swipeActive = this.active;
},
getSwipeRatio: function() {
return this.map.swipeRatio;
},
/*
* Method: updateRatio
* Update the swipeRatio and update the swipe control accordingly
*/
updateRatio: function(ratio) {
this.setSwipeRatio(ratio);
if (this.isLayersInLayerSwitcher()) {
this.div.style.display = 'block';
this.moveTo(this.computePosition());
this.clipFirstLayer();
} else {
this.div.style.display = 'none';
this.swipeLayer = null;
}
},
CLASS_NAME: "OpenLayers.Control.Swipe"
});这个js文件里面引用到了一些样式，样式文件的内容如下：.olControlSwipe {
background:url("../img/line.png") repeat;
display: none;
}
.olControlSwipeHover {
cursor: w-resize;
}
.olControlSwipeLayerView {
background-color: white;
height: 16px;
220px;
margin-top: 23px;
margin-left: -230px;
display: block;
font-size: 11px;
font-family: Tahoma, Arial;
font-weight: 700;
padding-top: 2px;
background-image: url("../img/bigarrow_left.png");
background-repeat: no-repeat;
position: absolute;
}
.olControlSwipeLayerSpan {
visibility: hidden;
font-size: 11px;
font-family: Tahoma, Arial;
font-weight: 700;
white-space: pre;
position: absolute;
}
.olControlSwipeLayerHide {
display: none;
}
.olControlArrowLeft {
16px;
height: 32px;
margin-left: -1px;
background-image: url("../img/bigarrow_left.png");
background-repeat: no-repeat;
position: absolute;
}
.olControlArrowRight {
16px;
height: 32px;
margin-left: 19px;
background-image: url("../img/bigarrow_right.png");
background-repeat: no-repeat;
position: absolute;
}最后，调用展示，代用代码如下：
$("#swipebutton").on("click",function(){
if(flag){
swipe.deactivate();
flag=false;
}
else{
swipe.activate();
flag=true;
}
});