My goal is to create a plugin that enables zooming & panning operations on a page area, just like how Google Maps currently works (meaning: scrolling with the mouse = zooming in/out of the area, click & hold & move & release = panning).
When scrolling, I wish to have a zoom operation centered on the mouse cursor.
For this, I use on-the-fly CSS3 matrix transformations. The only, yet mandatory, constraint is that I cannot use anything else than CSS3 translate & scale transformations, with a transform origin of 0px 0px.
Panning is out of the scope of my question, since I have it working already.
When it comes to zooming, I am struggling to figure out where the glitch is in my Javascript code.
The problem must be somewhere in the MouseZoom.prototype.zoom function, in the calculation of the translation on the x axis and y axis.
First, here is my HTML code:
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width = device-width, initial-scale = 1.0, user-scalable = no" />
<meta name="apple-mobile-web-app-capable" content="yes">
<meta name="apple-mobile-web-app-status-bar-style" content="black" />
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script src="jquery.mousewheel.min.js"></script>
<script src="StackOverflow.js"></script>
<style type="text/css" media="all">
#drawing {
position: absolute;
top: 0px;
left: 0px;
right:0;
bottom:0;
z-index: 0;
background: url(http://catmacros.files.wordpress.com/2009/09/cats_banzai.jpg) no-repeat;
background-position: 50% 50%;
}
</style>
<title>Test</title>
</head>
<body>
<div id="drawing"></div>
<script>
var renderer = new ZoomPanRenderer("drawing");
</script>
</body>
</html>
As you can see, I am using Jquery and the jquery mouse wheel plugin from Brandon Aaron, which can be found here:
https://github.com/brandonaaron/jquery-mousewheel/
Here is the content of the StackOverflow.js file:
/*****************************************************
* Transformations
****************************************************/
function Transformations(translateX, translateY, scale){
this.translateX = translateX;
this.translateY = translateY;
this.scale = scale;
}
/* Getters */
Transformations.prototype.getScale = function(){ return this.scale; }
Transformations.prototype.getTranslateX = function(){ return this.translateX; }
Transformations.prototype.getTranslateY = function(){ return this.translateY; }
/*****************************************************
* Zoom Pan Renderer
****************************************************/
function ZoomPanRenderer(elementId){
this.zooming = undefined;
this.elementId = elementId;
this.current = new Transformations(0, 0, 1);
this.last = new Transformations(0, 0, 1);
new ZoomPanEventHandlers(this);
}
/* setters */
ZoomPanRenderer.prototype.setCurrentTransformations = function(t){ this.current = t; }
ZoomPanRenderer.prototype.setZooming = function(z){ this.zooming = z; }
/* getters */
ZoomPanRenderer.prototype.getCurrentTransformations = function(){ return this.current; }
ZoomPanRenderer.prototype.getZooming = function(){ return this.zooming; }
ZoomPanRenderer.prototype.getLastTransformations = function(){ return this.last; }
ZoomPanRenderer.prototype.getElementId = function(){ return this.elementId; }
/* Rendering */
ZoomPanRenderer.prototype.getTransform3d = function(t){
var transform3d = "matrix3d(";
transform3d+= t.getScale().toFixed(10) + ",0,0,0,";
transform3d+= "0," + t.getScale().toFixed(10) + ",0,0,";
transform3d+= "0,0,1,0,";
transform3d+= t.getTranslateX().toFixed(10) + "," + t.getTranslateY().toFixed(10) + ",0,1)";
return transform3d;
}
ZoomPanRenderer.prototype.getTransform2d = function(t){
var transform3d = "matrix(";
transform3d+= t.getScale().toFixed(10) + ",0,0," + t.getScale().toFixed(10) + "," + t.getTranslateX().toFixed(10) + "," + t.getTranslateY().toFixed(10) + ")";
return transform3d;
}
ZoomPanRenderer.prototype.applyTransformations = function(t){
var elem = $("#" + this.getElementId());
elem.css("transform-origin", "0px 0px");
elem.css("-ms-transform-origin", "0px 0px");
elem.css("-o-transform-origin", "0px 0px");
elem.css("-moz-transform-origin", "0px 0px");
elem.css("-webkit-transform-origin", "0px 0px");
var transform2d = this.getTransform2d(t);
elem.css("transform", transform2d);
elem.css("-ms-transform", transform2d);
elem.css("-o-transform", transform2d);
elem.css("-moz-transform", transform2d);
elem.css("-webkit-transform", this.getTransform3d(t));
}
/*****************************************************
* Event handler
****************************************************/
function ZoomPanEventHandlers(renderer){
this.renderer = renderer;
/* Disable scroll overflow - safari */
document.addEventListener('touchmove', function(e) { e.preventDefault(); }, false);
/* Disable default drag opeartions on the element (FF makes it ready for save)*/
$("#" + renderer.getElementId()).bind('dragstart', function(e) { e.preventDefault(); });
/* Add mouse wheel handler */
$("#" + renderer.getElementId()).bind("mousewheel", function(event, delta) {
if(renderer.getZooming()==undefined){
var offsetLeft = $("#" + renderer.getElementId()).offset().left;
var offsetTop = $("#" + renderer.getElementId()).offset().top;
var zooming = new MouseZoom(renderer.getCurrentTransformations(), event.pageX, event.pageY, offsetLeft, offsetTop, delta);
renderer.setZooming(zooming);
var newTransformation = zooming.zoom();
renderer.applyTransformations(newTransformation);
renderer.setCurrentTransformations(newTransformation);
renderer.setZooming(undefined);
}
return false;
});
}
/*****************************************************
* Mouse zoom
****************************************************/
function MouseZoom(t, mouseX, mouseY, offsetLeft, offsetTop, delta){
this.current = t;
this.offsetLeft = offsetLeft;
this.offsetTop = offsetTop;
this.mouseX = mouseX;
this.mouseY = mouseY;
this.delta = delta;
}
MouseZoom.prototype.zoom = function(){
var previousScale = this.current.getScale();
var newScale = previousScale + this.delta/5;
if(newScale<1){
newScale = 1;
}
var ratio = newScale / previousScale;
var imageX = this.mouseX - this.offsetLeft;
var imageY = this.mouseY - this.offsetTop;
var previousTx = - this.current.getTranslateX() * previousScale;
var previousTy = - this.current.getTranslateY() * previousScale;
var previousDx = imageX * previousScale;
var previousDy = imageY * previousScale;
var newTx = (previousTx * ratio + previousDx * (ratio - 1)) / newScale;
var newTy = (previousTy * ratio + previousDy * (ratio - 1)) / newScale;
return new Transformations(-newTx, -newTy, newScale);
}
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