Drag and Drop Multiple Objects in HTML5 Canvas
I'm trying to implement an application in which the user can drag and drop multiple objects inside a given area..I'm using html5 canvas tag to implement this..When there is only one object to drag and drop inside the canvas then the code is working fine, but when i try to drag multiple objects independently inside the canvas then i'm not getting the desired output..
Here is the working example of drag and drop of only one object with the draw function
http://jsfiddle.net/KZ99q/
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
ctx.fillStyle = "#444444";
rect(x - 15, y - 15, 30, 30);
}
I thought adding more objects in draw() function will do so i added code for new objects in the draw() function like shown in this link
http://jsfiddle.net/KZ99q/1/
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
ctx.fillStyle = "#444444";
rect(x - 15, y - 15, 30, 30);
ctx.fillStyle = "#ff550d";
rect(x - 25, y - 25, 30, 30);
ctx.fillStyle = "#800080";
rect(x - 35, y - 35, 30, 30);
ctx.fillStyle = "#0c64e8";
rect(x - 45, y - 45, 30, 30);
}
I can't seem to understand what changes do i need to make in the MyMove(), MyUp() and MyDown() functions to make the objects move independently of one another.. Please Help
When moving 1 (or more) shapes, the procedure is:
Create objects that define each shape:
// an array of objects that define different rectangles
var rects=[];
rects.push({x:75-15,y:50-15,width:30,height:30,fill:"#444444",isDragging:false});
rects.push({x:75-25,y:50-25,width:30,height:30,fill:"#ff550d",isDragging:false});
rects.push({x:75-35,y:50-35,width:30,height:30,fill:"#800080",isDragging:false});
rects.push({x:75-45,y:50-45,width:30,height:30,fill:"#0c64e8",isDragging:false});
In mousedown:
isDragging flag on any shape that is under the mouse In mousemove:
In mouseup:
isDragging flags Here's annotated code and a Demo: http://jsfiddle.net/m1erickson/qm9Eb/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
window.onload=function(){
// get canvas related references
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var BB=canvas.getBoundingClientRect();
var offsetX=BB.left;
var offsetY=BB.top;
var WIDTH = canvas.width;
var HEIGHT = canvas.height;
// drag related variables
var dragok = false;
var startX;
var startY;
// an array of objects that define different rectangles
var rects=[];
rects.push({x:75-15,y:50-15,width:30,height:30,fill:"#444444",isDragging:false});
rects.push({x:75-25,y:50-25,width:30,height:30,fill:"#ff550d",isDragging:false});
rects.push({x:75-35,y:50-35,width:30,height:30,fill:"#800080",isDragging:false});
rects.push({x:75-45,y:50-45,width:30,height:30,fill:"#0c64e8",isDragging:false});
// listen for mouse events
canvas.onmousedown = myDown;
canvas.onmouseup = myUp;
canvas.onmousemove = myMove;
// call to draw the scene
draw();
// draw a single rect
function rect(x,y,w,h) {
ctx.beginPath();
ctx.rect(x,y,w,h);
ctx.closePath();
ctx.fill();
}
// clear the canvas
function clear() {
ctx.clearRect(0, 0, WIDTH, HEIGHT);
}
// redraw the scene
function draw() {
clear();
ctx.fillStyle = "#FAF7F8";
rect(0,0,WIDTH,HEIGHT);
// redraw each rect in the rects[] array
for(var i=0;i<rects.length;i++){
var r=rects[i];
ctx.fillStyle=r.fill;
rect(r.x,r.y,r.width,r.height);
}
}
// handle mousedown events
function myDown(e){
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// get the current mouse position
var mx=parseInt(e.clientX-offsetX);
var my=parseInt(e.clientY-offsetY);
// test each rect to see if mouse is inside
dragok=false;
for(var i=0;i<rects.length;i++){
var r=rects[i];
if(mx>r.x && mx<r.x+r.width && my>r.y && my<r.y+r.height){
// if yes, set that rects isDragging=true
dragok=true;
r.isDragging=true;
}
}
// save the current mouse position
startX=mx;
startY=my;
}
// handle mouseup events
function myUp(e){
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// clear all the dragging flags
dragok = false;
for(var i=0;i<rects.length;i++){
rects[i].isDragging=false;
}
}
// handle mouse moves
function myMove(e){
// if we're dragging anything...
if (dragok){
// tell the browser we're handling this mouse event
e.preventDefault();
e.stopPropagation();
// get the current mouse position
var mx=parseInt(e.clientX-offsetX);
var my=parseInt(e.clientY-offsetY);
// calculate the distance the mouse has moved
// since the last mousemove
var dx=mx-startX;
var dy=my-startY;
// move each rect that isDragging
// by the distance the mouse has moved
// since the last mousemove
for(var i=0;i<rects.length;i++){
var r=rects[i];
if(r.isDragging){
r.x+=dx;
r.y+=dy;
}
}
// redraw the scene with the new rect positions
draw();
// reset the starting mouse position for the next mousemove
startX=mx;
startY=my;
}
}
}; // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
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