<html>
<script type="text/javascript">
var canvas, ctx, flag = false,
prevX = 0,
currX = 0,
prevY = 0,
currY = 0,
dot_flag = false;
var x = "black",
y = 2;
function init() {
canvas = document.getElementById('can');
ctx = canvas.getContext("2d");
w = canvas.width;
h = canvas.height;
canvas.addEventListener("mousemove", function (e) {
findxy('move', e)
}, false);
canvas.addEventListener("mousedown", function (e) {
findxy('down', e)
}, false);
canvas.addEventListener("mouseup", function (e) {
findxy('up', e)
}, false);
canvas.addEventListener("mouseout", function (e) {
findxy('out', e)
}, false);
}
function color(obj) {
switch (obj.id) {
case "green":
x = "green";
break;
case "blue":
x = "blue";
break;
case "red":
x = "red";
break;
case "yellow":
x = "yellow";
break;
case "orange":
x = "orange";
break;
case "black":
x = "black";
break;
case "white":
x = "white";
break;
}
if (x == "white") y = 14;
else y = 2;
}
function draw() {
ctx.beginPath();
ctx.moveTo(prevX, prevY);
ctx.lineTo(currX, currY);
ctx.strokeStyle = x;
ctx.lineWidth = y;
ctx.stroke();
ctx.closePath();
}
function erase() {
var m = confirm("Want to clear");
if (m) {
ctx.clearRect(0, 0, w, h);
document.getElementById("canvasimg").style.display = "none";
}
}
function save() {
document.getElementById("canvasimg").style.border = "2px solid";
var dataURL = canvas.toDataURL();
document.getElementById("canvasimg").src = dataURL;
document.getElementById("canvasimg").style.display = "inline";
}
function findxy(res, e) {
if (res == 'down') {
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
flag = true;
dot_flag = true;
if (dot_flag) {
ctx.beginPath();
ctx.fillStyle = x;
ctx.fillRect(currX, currY, 2, 2);
ctx.closePath();
dot_flag = false;
}
}
if (res == 'up' || res == "out") {
flag = false;
}
if (res == 'move') {
if (flag) {
prevX = currX;
prevY = currY;
currX = e.clientX - canvas.offsetLeft;
currY = e.clientY - canvas.offsetTop;
draw();
}
}
}
</script>
<body onload="init()">
<canvas id="can" width="400" height="400" style="position:absolute;top:10%;left:10%;border:2px solid;"></canvas>
<div style="position:absolute;top:12%;left:43%;">Choose Color</div>
<div style="position:absolute;top:15%;left:45%;width:10px;height:10px;background:green;" id="green" onclick="color(this)"></div>
<div style="position:absolute;top:15%;left:46%;width:10px;height:10px;background:blue;" id="blue" onclick="color(this)"></div>
<div style="position:absolute;top:15%;left:47%;width:10px;height:10px;background:red;" id="red" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:45%;width:10px;height:10px;background:yellow;" id="yellow" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:46%;width:10px;height:10px;background:orange;" id="orange" onclick="color(this)"></div>
<div style="position:absolute;top:17%;left:47%;width:10px;height:10px;background:black;" id="black" onclick="color(this)"></div>
<div style="position:absolute;top:20%;left:43%;">Eraser</div>
<div style="position:absolute;top:22%;left:45%;width:15px;height:15px;background:white;border:2px solid;" id="white" onclick="color(this)"></div>
<img id="canvasimg" style="position:absolute;top:10%;left:52%;" style="display:none;">
<input type="button" value="save" id="btn" size="30" onclick="save()" style="position:absolute;top:55%;left:10%;">
<input type="button" value="clear" id="clr" size="23" onclick="erase()" style="position:absolute;top:55%;left:15%;">
</body>
</html>
I am developing a drawing app where two users can draw together. I am able to draw on one side, but i am not able how to draw the same line on other's pc with same pixel co-ordinates. This is the code which i am using on client side or say 1 pc
You question appears to be:
"How can I draw the same lines from the first computer on a different computer?"
First: Save
Save each new line segment into a format that can be transmitted over the internet--like JSON.
JSON.stringify takes a javascript object and converts it into a string format that can be transmitted through the internet. On the receiving side, JSON.parse converts the string back into a javascript object that you can use in your code.
var segment = {
startX:prevX,
startY:prevY,
endX:currX,
endY:currY,
color:x,
linewidth:y
};
var segmentJSON = JSON.stringify(segment);
Second: Send
Send your JSON string to the other computer. You give no information about how your 2 computers are connected, but one suggestion would be to use websockets for commumication. Websockets allow a continuous communication between 2+ computers using an intermediate server. One program (among many) implementing websockets is SocketIO:
Third: Receive and Replay
After receiving the JSON on the second computer, "replay" the drawing command.
var segment = JSON.parse(segmentJSON);
drawFromOtherComputer(segment);
function drawFromOtherComputer(segment) {
ctx.beginPath();
ctx.moveTo(segment.startingX, segment.startingY);
ctx.lineTo(segment.endingX, segment.endingY);
ctx.strokeStyle = segment.color;
ctx.lineWidth = segment.linewidth;
ctx.stroke();
}