Move (drag/pan) and zoom object (image or div) in pure js
I'm working on a little script that makes an object (div or img) moveable and zoomable within a given frame.
However I came across a few problems I'm not really sure of, because I'm a javascript beginner - so explanation of why those problems occure would be appreciated.
Problems:
- Calling the functions
start_drag(),while_drag()andstop_drag()returnsundefined- why is that? What should be returned? - The dragging and moving of the image does not work correctly - instead of clicking the mousebutton down and starting to move the image around, I have to click once and then start moving. Although I bound the
mousedownevent to the image. What did I do wrong? - Why is the moving part not working on mobile (the zooming works!)?
Please see my fiddle: https://jsfiddle.net/pow4ngbw/15/
Answer
Working fine now, was mainly the image css but found several errors (see the new img attribute), also added a few tweaks to make the dragging smoother.
<!DOCTYPE html>
<html>
<body>
<div id="container">
<img ondragstart="return false" id="drag-img" src="http://www.patsoy.com/p/2015/09/geometric-patterns-f03phtdx.jpg" />
</div>
<input type="button" id="zoomout" class="button" value="Zoom out">
<input type="button" id="zoomin" class="button" value="Zoom in">
</body>
</html>
<script>
var img_ele = null,
x_cursor = 0,
y_cursor = 0,
x_img_ele = 0,
y_img_ele = 0;
function zoom(zoomincrement) {
img_ele = document.getElementById('drag-img');
var pre_width = img_ele.getBoundingClientRect().width, pre_height = img_ele.getBoundingClientRect().height;
img_ele.style.width = (pre_width * zoomincrement) + 'px';
img_ele.style.height = (pre_height * zoomincrement) + 'px';
img_ele = null;
}
document.getElementById('zoomout').addEventListener('click', function() {
zoom(0.5);
});
document.getElementById('zoomin').addEventListener('click', function() {
zoom(1.5);
});
function start_drag() {
img_ele = this;
x_img_ele = window.event.clientX - document.getElementById('drag-img').offsetLeft;
y_img_ele = window.event.clientY - document.getElementById('drag-img').offsetTop;
}
function stop_drag() {
img_ele = null;
}
function while_drag() {
var x_cursor = window.event.clientX;
var y_cursor = window.event.clientY;
if (img_ele !== null) {
img_ele.style.left = (x_cursor - x_img_ele) + 'px';
img_ele.style.top = ( window.event.clientY - y_img_ele) + 'px';
console.log(img_ele.style.left+' - '+img_ele.style.top);
}
}
document.getElementById('drag-img').addEventListener('mousedown', start_drag);
document.getElementById('container').addEventListener('mousemove', while_drag);
document.getElementById('container').addEventListener('mouseup', stop_drag);
</script>
<style>
#drag-img {
cursor: move;
position: relative;
width: 500px;
height: 500px;
}
#container {
overflow: hidden;
background: red;
height: 500px;
width: 500px;
}
.button {
width: 200px;
height: 50px;
}
</style>