Develop Reference

How do I calculate and determine the area at which the div must be dropped?

I am building a drag and drop application purely in Javascript. I have coded the drag part where the element can be dragged and dropped randomly in the page. Now, I have built a drop zone that contains 9 boxes(divs) wherein 9 divs must be dropped. I can't think of an approach that will help me accomplish this task. I am thinking of making those divs 'absolute' and re-build them use top & left attributes. But how should I proceed further? How will the div that I drag i.e onmousedown will come to know that onmouseup it should drop at the specified location. Example: If I select a div numbered 1, it should drop at target numbered 1.
Here's the Javascript I am using for selecting and dragging:
window.onload = function() {
var el = document.getElementById('block1');
var mover = false, x, y, posx, posy, first = true;
el.onmousedown = function() {
mover = true;
};
el.onmouseup = function() {
mover = false;
first = true;
};
el.onmousemove = function(e) {
if (mover) {
if (first) {
x = e.offsetX;
y = e.offsetY;
first = false;
}
posx = e.pageX - x;
posy = e.pageY - y;
this.style.left = posx + 'px';
this.style.top = posy + 'px';
}
};
};

I would have the targets recognize a "onmouseenter" and set a Boolean to be true for that target, then set it to false "onmouseleave". then "onmouseup" check all of the booleans and if div1 has been dropped and target1 is true then div1 position = target position.
I know this is a pseudo code answer but its just my thought process on ho to solve the problem.

Detect container, while moving an element over it

I making a simple drag'n'drop interface. I have a bunch of containers ("wrapper") and some dynamically added items ("dragElement") in one of them. So I need, when I move item over another container, JS detect it and move the item there when the drag is finished.
I tried to detect container with "onmouseover" and "mouseup" when dragging item, but had no success, because, actually, mouse always was over the dragged element.
So how can I detect container when drag item? In pure JS please...
document.onmousedown = function(e) {
var dragElement = e.target;
if (!dragElement.classList.contains('draggable')) return;
var coords, shiftX, shiftY, detectPage;
startDrag(e.clientX, e.clientY);
document.onmousemove = function(e) {
moveAt(e.clientX, e.clientY);
};
wrapper.onmouseover = function(e) {
detectPage = e.target;
console.log(detectPage);
};
dragElement.onmouseup = function() {
finishDrag();
};
function startDrag(clientX, clientY) {
shiftX = clientX - dragElement.getBoundingClientRect().left;
shiftY = clientY - dragElement.getBoundingClientRect().top;
dragElement.style.position = 'fixed';
document.body.appendChild(dragElement);
moveAt(clientX, clientY);
};
function finishDrag() {
dragElement.style.top = parseInt(dragElement.style.top) - wrapper.getBoundingClientRect().top + 'px';
dragElement.style.position = 'absolute';
wrapper.onmouseup = function(e) {
var selectPage = e.target;
}
wrapper.appendChild(dragElement);
document.onmousemove = null;
dragElement.onmouseup = null;
};
function moveAt(clientX, clientY) {
var newX = clientX - shiftX;
var newY = clientY - shiftY;
if (newX < 0) newX = 0;
if (newX > wrapper.offsetWidth - dragElement.offsetWidth) {
newX = wrapper.offsetWidth - dragElement.offsetWidth;
}
dragElement.style.left = newX + 'px';
dragElement.style.top = newY + 'px';
};
return false;
};

Well, no one help. So one free day gone to find the solution. All I can found is to delete function finishDrag() from dragElement.onmouseup and change it to the code below.
If in shorter, when onmouseup comes, dragElement must go to display:none and now we can get access to the object near the mouse cursor through elementFromPoint. When we done with it, we can easily detects container, bring an element back to display:block and put it to that container...
Hope, it helps to someone...
dragElement.onmouseup = function(e) {
dragElement.style.display = 'none';
var selectPage = document.elementFromPoint(e.clientX, e.clientY);
dragElement.style.display = 'block';
dragElement.style.top = parseInt(dragElement.style.top) - selectPage.getBoundingClientRect().top + 'px';
dragElement.style.position = 'absolute';
selectPage.appendChild(dragElement);
document.onmousemove = null;
dragElement.onmouseup = null;
};

jQuery Volume Slider

seems like I cannot find a solution for this. Please Help me out.
What I want to do is to have a simple volume slider.
SO, as you can see the orange part is my volume slider.
This is my jQuery:
var mouseDown = false;
$("#volSlider").mousedown(function() { mouseDown = true; });
$("#volSlider").mouseup(function() { mouseDown = false; });
$("#volSlider").mouseleave(function() { mouseDown = false; });
$("#controlVolume").mousemove(function(e)
{
if (mouseDown == true)
{
var caretFromTop = $("#volCaret").position().top;
var areaHeight = $("#volSlider").height();
var volume = (caretFromTop / areaHeight) * 100;
volume = Math.round(volume);
$("#volCaret").css("bottom", volume);
$("#volText").text(volume);
if (volume <= 100 && volume >= 0)
{
//To be added.
}
}
});
EDIT: For those who want to see my HTML:
<div id="controlVolume">
<div id="volSlider">
<div id="volCaret"></div>
</div>
<div id="volText"></div>
</div>
When i try to drag the caret to the top, it just goes to "1" and not further. Anything I am missing? Thanks in advance.

What you actually want to do is track the Y vertex of the mouse, not the height of the caret (well, technically yes - the height of the caret that changes between the mouse moves). You're currently tracking the position of the volume bar, which doesn't change.
As such your code should be something like this:
var mousePos = 0;
var mouseDown = false;
var height = 0;
$("#volSlider").mousedown(function(e) { mouseDown = true; mousePos = e.pageY; height = $("#volCaret").height(); });
$("#volSlider").mouseup(function() { mouseDown = false; mousePos = 0 });
$("#volSlider").mouseleave(function() { mouseDown = false; mousePos = 0 });
$("#controlVolume").mousemove(function(e)
{
if (mouseDown == true)
{
var areaHeight = $("#volSlider").height();
var caretHeight = height + (e.pageY - mousePos);
$("#volCaret").height(caretHeight );
var volume = caretHeight / areaHeight * 100;
console.log(volume);
}
});
It would be great if you'd put your code on jsfiddle, as probably there's something I've not thought of and this code fails horribly.

Clicakble planets

Im trying to make planets that give an alert message when clicked.
Problem is, onmousedown only works on canvas, as far I tested.
Code for planets:
var planets = [];
for (var b=0;b<3;b++) {
planets.push(planet(0,360,Math.random()*600,Math.random()*600));
}
function planet(I,shiips,xpos,ypos){
I = I||{};
I.ships = shiips;
I.x=xpos;
I.y=ypos;
return I;
}
code for click detection; tests both for planet object and the image
update = function(){
planetImage.onmousedown=function(){alert("works!")};
planets[0].onmousedown=function(){alert("works!")};
}
setInterval(update,100);
Im using canvas to draw the images, if that hhelps.
I found the following code that gives mouse position, but it doesnt work for me:
(function() {
var mousePos;
window.onmousemove = handleMouseMove;
setInterval(getMousePosition, 100); // setInterval repeats every X ms
function handleMouseMove(event) {
event = event || window.event; // IE-ism
mousePos = {
x: event.clientX,
y: event.clientY
};
}
function getMousePosition() {
var pos = mousePos;
if (!pos) {
// We haven't seen any movement yet
}
else {
// Use pos.x and pox.y
}
}
})();
Im trying to keep it simple, I don't really like jquery or anything complicated.
Once again: the problem is onmousedown only works on the canvas object, i.e.
canvas.onmousedown=function(){alert("works!")};

I got it working now with this code:
update = function(){
canvas.onmousedown=function(){
var e = window.event;
var posX = e.clientX;
var posY = e.clientY;
alert("X position: "+ posX + " Y position: " + posY);
};
setInterval(update,100);

Implement dragging an image within a canvas

I want to implement dragging of an image within a canvas. I want simplest code for that. So far I have seen a lot of examples but they have used complex ways of implementation. I want an example that is easy to learn and implement.

It's pretty difficult. You'll first need to write a function that can detect when you click a particular element. However, before we can do that, we must define what we mean by "element". Is it the product of a single draw instruction (e.g. a rectangle or arc), or something complex? (Imagine I wanted to draw a cat and make the entire cat draggable as a unit.)
A canvas is nothing but a collection of pixels. If you want your program to have an idea of "shapes" or even "collections of shapes treated as a unit" you'll need to implement them yourself as data structures external to the canvas itself. Once you have that, you can write an onmousedown handler that takes the x/y point clicked and determine what shape (if any) the click falls inside of (and if it falls inside of multiple shapes, check which has the foremost z-index). Then add an onmousemove handler that erases and redraws the shape on the canvas based on the information in the shape data object.
This is a moderately difficult problem with very difficult prerequisite problems (creating data structures that can describe a wide range of shapes as well as collections of shapes). I highly recommend you use a canvas drawing library that has already solved these problems. I use cake.js but there are loads of options available.

If you don't have to use the HTML5 canvas, jQuery UI is a lot simpler:
HTML:
<img class="drag-me" src="http://www.google.com/images/srpr/logo3w.png">​
JavaScript:
$(function() {
$('.drag-me').draggable();
});
​
See it in action:
http://jsfiddle.net/flackend/TQzSe/
The jQuery UI API has a lot of options too to make it act how you want:
http://jqueryui.com/demos/draggable/
Plus, if it doesn't do what you need, it's easy to implement yourself. Post here if you need help with that.

jsfiddle.net/Zevan/QZejF/5 This may help you.
<html>
<head>
<title>Test Page</title>
<script type="text/javascript" src="jquery.js"></script>
</head>
<body>
<canvas id="c" width = "500" height = "500" ></canvas>
<script type="text/javascript">
var canvas = $("#c");
var c = canvas[0].getContext("2d");
//var path = "http://wonderfl.net/images/icon/e/ec/ec3c/ec3c37ba9594a7b47f1126b2561efd35df2251bfm";
var path = "blue.jpg";
var path2 = "purple.jpg";
var image1 = new DragImage(path, 200, 100);
var image2 = new DragImage(path2, 300, 100);
var loop = setInterval(function() {
c.fillStyle = "gray";
c.fillRect(0, 0, 500, 500);
image1.update();
image2.update();
}, 30);
var mouseX = 0,
mouseY = 0;
var mousePressed = false;
var dragging = false;
canvas.mousemove(function(e) {
mouseX = e.offsetX;
mouseY = e.offsetY;
})
$(document).mousedown(function() {
mousePressed = true;
}).mouseup(function() {
mousePressed = false;
dragging = false;
});
function DragImage(src, x, y) {
var that = this;
var startX = 0,
startY = 0;
var drag = false;
this.x = x;
this.y = y;
var img = new Image();
img.src = src;
this.update = function() {
if (mousePressed ) {
var left = that.x;
var right = that.x + img.width;
var top = that.y;
var bottom = that.y + img.height;
if (!drag) {
startX = mouseX - that.x;
startY = mouseY - that.y;
}
if (mouseX < right && mouseX > left && mouseY < bottom && mouseY > top) {
if (!dragging){
dragging = true;
drag = true;
}
}
} else {
drag = false;
}
if (drag) {
that.x = mouseX - startX;
that.y = mouseY - startY;
}
c.drawImage(img, that.x, that.y);
}
}
</script>
</body>
</html>