Building a multiplayer doodle using fabric js.
Trying to implement multiplayer doodle using fabric js, the idea is when U1 draws on canvas we push the points to RTDB and get those points on both the client and programmatically draw the stroke in both the clients.
You can save the canvas' data on path:created for example (or other event) using toJSON().Send it to the server and the other client will load it using loadFromJSON().
Update (4.3.1) (Thanks to #user8555937)
const pointer = canvas.getPointer(e);
const options = {pointer, e:{}} // required for Fabric 4.3.1
canvas2.freeDrawingBrush.onMouseDown(pointer, options);
var canvas = new fabric.Canvas(document.getElementById('canvasId'))
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.width = 5;
canvas.freeDrawingBrush.color = '#00aeff';
canvas.on('path:created', function(e) {
e.path.set();
canvas.renderAll();
drawOnCanvas(canvas.toJSON());
});
var canvas2 = new fabric.Canvas(document.getElementById('canvasId2'));
function drawOnCanvas(json) {
canvas2.loadFromJSON(json);
}
#app {
display: flex;
}
canvas {
border: 1px solid red;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.19/fabric.min.js"></script>
<div id="app">
<canvas id="canvasId" width="400" height="400"></canvas>
<canvas id="canvasId2" width="400" height="400"></canvas>
</div>
Probably you can optimize it by sending only the diffs and so on, but this is the start of the path
Sync on drawing (not only after path:created)
The idea is to "capture" the "original" canvas' events and trigger them on the second one.
So, you can send the pointer to the server and trigger the events in the other clients.
var canvas = new fabric.Canvas(document.getElementById('canvasId'))
canvas.isDrawingMode = true;
canvas.freeDrawingBrush.width = 5;
canvas.freeDrawingBrush.color = '#00aeff';
let isDrawing = false;
canvas.on('mouse:down', function({e}) {
isDrawing = true;
onMouseDown(e);
}).on('mouse:up', function({e}) {
isDrawing = false;
onMouseUp(e);
}).on('mouse:move', function({e}) {
if (isDrawing) {
const pointer = canvas.getPointer(e);
drawRealTime(e, pointer);
}
});
var canvas2 = new fabric.Canvas(document.getElementById('canvasId2'));
canvas2.isDrawingMode = true;
canvas2.freeDrawingBrush.width = 5;
canvas2.freeDrawingBrush.color = '#00aeff';
function onMouseDown(e) {
const pointer = canvas.getPointer(e);
canvas2.freeDrawingBrush.onMouseDown(pointer);
}
function onMouseUp(e) {
const pointer = canvas.getPointer(e);
canvas2.freeDrawingBrush.onMouseUp(pointer);
}
function drawRealTime(e, pointer) {
canvas2.freeDrawingBrush.onMouseMove(pointer);
}
#app {
display: flex;
}
canvas {
border: 1px solid red;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/fabric.js/1.7.19/fabric.min.js"></script>
<div id="app">
<canvas id="canvasId" width="400" height="400"></canvas>
<canvas id="canvasId2" width="400" height="400"></canvas>
</div>
https://codepen.io/moshfeu/pen/ZEGQEBO?editors=0010
Related
i am trying to create an image canvas where user can zoom into the image, the code which i got from here enter link description here, now i tried to add image inside it and i did the following code:
function draw(scale, translatePos) {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
make_base(context);
}
function make_base(context) {
var base_image = new Image();
base_image.src = 'https://www.gstatic.com/webp/gallery3/1.sm.png';
base_image.onload = function() {
context.drawImage(base_image, 0, 0);
}
}
window.onload = function() {
var canvas = document.getElementById("myCanvas");
var translatePos = {
x: canvas.width / 2,
y: canvas.height / 2
};
var scale = 1.0;
var scaleMultiplier = 0.8;
var startDragOffset = {};
var mouseDown = false;
// add button event listeners
document.getElementById("plus").addEventListener("click", function() {
scale /= scaleMultiplier;
draw(scale, translatePos);
}, false);
document.getElementById("minus").addEventListener("click", function() {
scale *= scaleMultiplier;
draw(scale, translatePos);
}, false);
// add event listeners to handle screen drag
canvas.addEventListener("mousedown", function(evt) {
mouseDown = true;
startDragOffset.x = evt.clientX - translatePos.x;
startDragOffset.y = evt.clientY - translatePos.y;
});
canvas.addEventListener("mouseup", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mouseover", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mouseout", function(evt) {
mouseDown = false;
});
canvas.addEventListener("mousemove", function(evt) {
if (mouseDown) {
translatePos.x = evt.clientX - startDragOffset.x;
translatePos.y = evt.clientY - startDragOffset.y;
draw(scale, translatePos);
}
});
draw(scale, translatePos);
};
jQuery(document).ready(function() {
$("#wrapper").mouseover(function(e) {
$('#status').html(e.pageX + ', ' + e.pageY);
});
})
body {
margin: 0px;
padding: 0px;
}
#wrapper {
position: relative;
border: 1px solid #9C9898;
width: 578px;
height: 200px;
}
#buttonWrapper {
position: absolute;
width: 30px;
top: 2px;
right: 2px;
}
input[type="button"] {
padding: 5px;
width: 30px;
margin: 0px 0px 2px 0px;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<body onmousedown="return false;">
<div id="wrapper">
<canvas id="myCanvas" width="578" height="200">
</canvas>
<div id="buttonWrapper">
<input type="button" id="plus" value="+"><input type="button" id="minus" value="-">
</div>
</div>
<h2 id="status">
0, 0
</h2>
</body>
however the image is not getting displayed inside the canvas, can anyone please tell me what could be wrong in here, thanks in advance
Your draw function never actually draws to the canvas. You get the canvas and context in the first 2 lines, but you need to call drawImage with the image to actually add it to the canvas itself.
I suspect you want to be calling make_base inside it like so:
function draw(scale, translatePos) {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
make_base();
}
You also need to have the context in the same scope as you use it. At the moment, the variable context only exists inside the draw function and not the make_base function, so you can't access it from inside make_base.
You can pass it as a variable like so:
function draw(scale, translatePos) {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
make_base(context);
}
function make_base(context) {
var base_image = new Image();
base_image.src = 'a2.jpg';
base_image.onload = function() {
context.drawImage(base_image, 0, 0);
}
}
Every time you want to change anything on an HTML canvas you need to call draw functions to change what's there.
I've written a small javascript application that uses the mouse to draw lines on a canvas, captures that stream, and then creates a video. After that video is created, it attaches it to a <video> tag.
When I run this on Chrome, it runs completely fine.
When I run this on Firefox, it returns a completely black video. The time length of the video is correct though.
More bizarrely, when I save the video from Chrome (via right-click and "save video as..."), the file it saves to shows up as completely black.
I attempted to stream the video as I drew to see if the issue had to do with the .captureStream() function. That works fine however. My gut tells me the issue is from the MediaRecorder format but I'm not 100% certain as I confirmed that firefox supports this video format with MediaRecorder.isTypeSupported(`video/webm;codecs=vp8`)
I'm running Firefox 78.0.2 under Ubuntu 18.04. Code is below:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<title>Document</title>
</head>
<style>
canvas {
border: 1px solid black;
cursor: crosshair;
}
.canvas-holder {
width: 40%;
float: left;
display: inline-block;
}
.video-holder {
width: 40%;
float: left;
display: inline-block;
}
</style>
<body>
<div class="canvas-holder">
<canvas id="mycanvas" width="300" height="300"></canvas>
<button id="save-button">Save Canvas</button>
<button id="start-button">Start Recording</button>
<button id="stop-button">Stop Recording</button>
</div>
<div class="video-holder">
<video id="stream-video" width="300" height="300"></video>
<video id="myvideo" width="300" height="300"></video>
</div>
</body>
<script>
var canvas = document.querySelector("canvas#mycanvas");
var ctx = canvas.getContext("2d");
ctx.lineWidth = 5;
ctx.lineCap = "round";
ctx.shadowBlur = 1; // helps with jagged edges
ctx.shadowColor = "black";
// drawing logic
mouse = { x: 0, y: 0, moveflag: false };
canvas.addEventListener("mousedown", e => draw("mousedown", e), false);
canvas.addEventListener("mousemove", e => draw("mousemove", e), false);
canvas.addEventListener("mouseup", e => draw("mouseup", e), false);
function draw(res, e) {
if (res == "mousedown") {
// begin drawing
mouse.moveflag = true;
} else if (res == "mousemove" && mouse.moveflag) {
mouse.x = e.offsetX; // this compensates for the canvas being slightly off
mouse.y = e.offsetY;
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();
} else if (res == "mouseup" && mouse) {
mouse.moveflag = false;
ctx.beginPath();
} else {
return;
}
}
// saving logic
saveButton = document.querySelector("#save-button");
saveButton.onclick = e => {
e.preventDefault();
console.log("saved!");
var image = canvas.toDataURL("image/png");
// window.location.href = image; // redirect to saved image
console.log("Image, base64 encoded => ", image);
};
// video logic
const videoTag = document.querySelector("video#myvideo");
const streamVideo = document.querySelector("video#stream-video");
const startButton = document.querySelector("button#start-button");
const stopButton = document.querySelector("button#stop-button");
const stream = canvas.captureStream();
streamVideo.srcObject = stream;
var mediaRecorder = new MediaRecorder(stream, {
mimeType: `video/webm;codecs=vp8`
});
let chunks = [];
mediaRecorder.ondataavailable = e => {
console.log("chunking data");
chunks.push(e.data);
};
mediaRecorder.onstop = e => {
console.log("stopping mediaRecorder");
var blob = new Blob(chunks, {
type: `video/webm;codecs=vp8`
});
// create a local URL and set the video to that
// its all black!
const videoURL = window.URL.createObjectURL(blob);
videoTag.src = videoURL;
videoTag.play();
};
startButton.onclick = e => {
e.preventDefault();
mediaRecorder.start();
console.log("start recording");
};
stopButton.onclick = e => {
e.preventDefault();
mediaRecorder.stop();
console.log("stop recording");
};
</script>
</html>
I am trying to creat a minesweeper board in Javascript, but first i tried to creat only one cell. this is my code. It was suppose to draw a cell from the 30px width and 30px height picture that i created ( cell.png ) but when i run the code i only see the canvas. What am i doing wrong?
<!DOCTYPE html>
<html>
<head>
<script>
var s = {
rows: 10,
col: 10,
width: 30,
height: 30,
};
var c;
window.onload = function(){
var canvas = document.getElementById("myCanvas");
c = canvas.getContext("2d");
// c.fillRect(50,50,300,300);
init();
}
var box;
function init(){
box = new Image();
box.src = "cell.png";
draw();
}
function draw(){
c.clearRect(0,0,400,400);
c.drawImage(box,10,10);
}
</script>
</head>
<body>
<div id="controls">
</div>
<div id="game">
<canvas id="myCanvas" width="400" height="400" style="border:1px solid #c3c3c3;">
</canvas>
</div>
</body>
</html>
The problem you are experiencing is because your code is not waiting for the image to load before trying to draw it. You need to wait till it is loaded then call the drawing code, this can be done from the image's onload event
var s = {
rows: 10,
col: 10,
width: 30,
height: 30,
};
var c;
window.onload = function(){
var canvas = document.getElementById("myCanvas");
c = canvas.getContext("2d");
init();
}
var box;
function init(){
box = new Image();
//onload will be called once the image has loaded
box.onload = function(){
//Here you call draw.
draw();
};
box.src = "http://placehold.it/30x30"; //"cell.png";
}
function draw(){
c.clearRect(0,0,400,400);
c.drawImage(box,10,10);
}
<canvas width="200" height="200" id="myCanvas"></canvas>
I want to be able to spawn a new image to the canvas at the click of a button, rather than having to manually edit the code.
I have the following HTML5/JavaScript code that allows images to be dragged and dropped between multiple canvases and it works perfectly for what I require.
What I am doing:
<canvas style="float: left" height="125" width="400" id="cvs1">[No canvas support]</canvas>
<canvas style="float: left; margin-left: 100px" height="125" width="400" id="cvs2">[No canvas support]</canvas>
<script src="http://www.rgraph.net/libraries/RGraph.common.core.js" ></script>
<script>
window.onload = function ()
{
var canvas1 = document.getElementById("cvs1");
var canvas2 = document.getElementById("cvs2");
var context1 = canvas1.getContext('2d');
var context2 = canvas2.getContext('2d');
var imageXY = {x: 5, y: 5};
/**
* This draws the image to the canvas
*/
function Draw ()
{
//Clear both canvas first
canvas1.width = canvas1.width
canvas2.width = canvas2.width
//Draw a red rectangle around the image
if (state && state.dragging) {
state.canvas.getContext('2d').strokeStyle = 'red';
state.canvas.getContext('2d').strokeRect(imageXY.x - 2.5,
imageXY.y - 2.5,
state.image.width + 5,
state.image.height + 5);
}
// Now draw the image
state.canvas.getContext('2d').drawImage(state.image, imageXY.x, imageXY.y);
}
canvas2.onclick =
canvas1.onclick = function (e)
{
if (state && state.dragging) {
state.dragging = false;
Draw();
return;
}
var mouseXY = RGraph.getMouseXY(e);
state.canvas = e.target;
if ( mouseXY[0] > imageXY.x
&& mouseXY[0] < (imageXY.x + state.image.width)
&& mouseXY[1] > imageXY.y
&& mouseXY[1] < (imageXY.y + state.image.height)) {
state.dragging = true;
state.originalMouseX = mouseXY[0];
state.originalMouseY = mouseXY[1];
state.offsetX = mouseXY[0] - imageXY.x;
state.offsetY = mouseXY[1] - imageXY.y;
}
}
canvas1.onmousemove =
canvas2.onmousemove = function (e)
{
if (state.dragging) {
state.canvas = e.target;
var mouseXY = RGraph.getMouseXY(e);
// Work how far the mouse has moved since the mousedon event was triggered
var diffX = mouseXY[0] - state.originalMouseX;
var diffY = mouseXY[1] - state.originalMouseY;
imageXY.x = state.originalMouseX + diffX - state.offsetX;
imageXY.y = state.originalMouseY + diffY - state.offsetY;
Draw();
e.stopPropagation();
}
}
/**
* Load the image on canvas1 initially and set the state up with some defaults
*/
state = {}
state.dragging = false;
state.canvas = document.getElementById("cvs1");
state.image = new Image();
state.image.src = 'http://www.rgraph.net/images/logo.png';
state.offsetX = 0;
state.offsetY = 0;
state.image.onload = function ()
{
Draw();
}
}
</script>
This can also be seen on this JS Fiddle (Note: you have to click the image before you can drag it)
The problem I am having:
I would like to add more images to the canvases so that any of the images can then be dragged and dropped between however many canvases I choose to create.
I can quite easily add more canvases to the page to drag and drop between, however when it comes to adding/spawning more images to the canvases I cannot get it to work.
The only way I can think of being able to do this is by repeating the Draw() function for every single image that gets added. That would mean if I wanted 30 images to be able to drag and drop between 10 different canvases for example, I would need to repeat the Draw() function 30 times. Surely that cannot be the best way to do this?
Unless I am missing something very obvious I cannot see another way of doing this?
Here’s how to configure your code to create multiple objects and click-drag between canvases.
Demo: http://jsfiddle.net/m1erickson/Bnb6A/
Code an object factory function that creates new draggable objects and put all new objects in an array.
Keep this information about each draggable object:
dragging (true/false) indicating if this object is currently being dragged
image: the image for this object
x,y: the current top,left position of this object
width,height: the size of this object
offsetX,offsetY: indicates where the mouse clicked relative to top,left of this object
draw: (a function) that allows this object to draw itself (surrounded by a red rect if it’s being dragged)
On click:
Get the mouse position
Clear both canvases
Iterate through the object array
If an object is being dragged, unset the dragging flag
If an object is now selected, set the dragging flag and set the offsetX,offsetY for the starting mouse position relative to this object.
Redraw all objects
On mousemove:
Get the mouse position
Clear both canvases
Iterate through the object array
If an object is being dragged, move it to the mouse position (setting x,y adjusted for the offset)
Redraw all objects
Code:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:20px; }
canvas{ border: 1px solid #808080; }
</style>
<script>
$(function(){
var canvas1 = document.getElementById("cvs1");
var canvas2 = document.getElementById("cvs2");
var contexts=[];
contexts.push(canvas1.getContext('2d'));
contexts.push(canvas2.getContext('2d'));
function clearAll(){
//Clear both canvas first
canvas1.width = canvas1.width
canvas2.width = canvas2.width
}
canvas1.onclick=function(e){ handleClick(e,1); };
canvas2.onclick=function(e){ handleClick(e,2); };
//
function handleClick(e,contextIndex){
e.stopPropagation();
var mouseX=parseInt(e.clientX-e.target.offsetLeft);
var mouseY=parseInt(e.clientY-e.target.offsetTop);
clearAll();
for(var i=0;i<states.length;i++){
var state=states[i];
if(state.dragging){
state.dragging=false;
state.draw();
continue;
}
if ( state.contextIndex==contextIndex
&& mouseX>state.x && mouseX<state.x+state.width
&& mouseY>state.y && mouseY<state.y+state.height)
{
state.dragging=true;
state.offsetX=mouseX-state.x;
state.offsetY=mouseY-state.y;
state.contextIndex=contextIndex;
}
state.draw();
}
}
canvas1.onmousemove = function(e){ handleMousemove(e,1); }
canvas2.onmousemove = function(e){ handleMousemove(e,2); }
//
function handleMousemove(e,contextIndex){
e.stopPropagation();
var mouseX=parseInt(e.clientX-e.target.offsetLeft);
var mouseY=parseInt(e.clientY-e.target.offsetTop);
clearAll();
for(var i=0;i<states.length;i++){
var state=states[i];
if (state.dragging) {
state.x = mouseX-state.offsetX;
state.y = mouseY-state.offsetY;
state.contextIndex=contextIndex;
}
state.draw();
}
}
var states=[];
var img=new Image();
img.onload=function(){
states.push(addState(0,0,img));
}
img.src="http://www.rgraph.net/images/logo.png";
function addState(x,y,image){
state = {}
state.dragging=false;
state.contextIndex=1;
state.image=image;
state.x=x;
state.y=y;
state.width=image.width;
state.height=image.height;
state.offsetX=0;
state.offsetY=0;
state.draw=function(){
var context=contexts[this.contextIndex-1];
if (this.dragging) {
context.strokeStyle = 'red';
context.strokeRect(this.x,this.y,this.width+5,this.height+5)
}
context.drawImage(this.image,this.x,this.y);
}
state.draw();
return(state);
}
$("#more").click(function(){
states.push(addState(states.length*100,0,img));
});
}); // end $(function(){});
</script>
</head>
<body>
<button id="more">Add Image</button><br>
<canvas height="125" width="300" id="cvs1">[No canvas support]</canvas><br>
<canvas height="125" width="300" id="cvs2">[No canvas support]</canvas>
</body>
</html>
I have have a problem I am hoping someone will be able to help with...
On my application I require the facility to be able to drag and drop images between multiple canvases.
There are a few pre-made examples of dragging and dropping between multiple canvases avaliable online, and I have found the perfect example for my needs courtesy of 'Richard Heyes' of RGraph which you can see here (NOTE: you must click the image before you can start dragging it).
As you can see, on his website this drag and drop feature works perfectly, however when I transfer the javascript, html and css to my application the ability to drag and drop the image does not work.
What I am doing:
<!DOCTYPE html>
<html>
<body>
<h1>My First Heading</h1>
<p>My first paragraph.</p>
<style type="text/css">
canvas {
border: 1px solid #808080;
}
</style>
<canvas style="float: left" height="125" width="400" id="cvs1">[No canvas support]</canvas>
<canvas style="float: left; margin-left: 100px" height="125" width="400" id="cvs2">[No canvas support]</canvas>
<script>
window.onload = function ()
{
var canvas1 = document.getElementById("cvs1");
var canvas2 = document.getElementById("cvs2");
var context1 = canvas1.getContext('2d');
var context2 = canvas2.getContext('2d');
var imageXY = {x: 5, y: 5};
/**
* This draws the image to the canvas
*/
function Draw ()
{
//Clear both canvas first
canvas1.width = canvas1.width
canvas2.width = canvas2.width
//Draw a red rectangle around the image
if (state && state.dragging) {
state.canvas.getContext('2d').strokeStyle = 'red';
state.canvas.getContext('2d').strokeRect(imageXY.x - 2.5,
imageXY.y - 2.5,
state.image.width + 5,
state.image.height + 5);
}
// Now draw the image
state.canvas.getContext('2d').drawImage(state.image, imageXY.x, imageXY.y);
}
canvas2.onclick =
canvas1.onclick = function (e)
{
if (state && state.dragging) {
state.dragging = false;
Draw();
return;
}
var mouseXY = RGraph.getMouseXY(e);
state.canvas = e.target;
if ( mouseXY[0] > imageXY.x
&& mouseXY[0] < (imageXY.x + state.image.width)
&& mouseXY[1] > imageXY.y
&& mouseXY[1] < (imageXY.y + state.image.height)) {
state.dragging = true;
state.originalMouseX = mouseXY[0];
state.originalMouseY = mouseXY[1];
state.offsetX = mouseXY[0] - imageXY.x;
state.offsetY = mouseXY[1] - imageXY.y;
}
}
canvas1.onmousemove =
canvas2.onmousemove = function (e)
{
if (state.dragging) {
state.canvas = e.target;
var mouseXY = RGraph.getMouseXY(e);
// Work how far the mouse has moved since the mousedon event was triggered
var diffX = mouseXY[0] - state.originalMouseX;
var diffY = mouseXY[1] - state.originalMouseY;
imageXY.x = state.originalMouseX + diffX - state.offsetX;
imageXY.y = state.originalMouseY + diffY - state.offsetY;
Draw();
e.stopPropagation();
}
}
/**
* Load the image on canvas1 initially and set the state up with some defaults
*/
state = {}
state.dragging = false;
state.canvas = document.getElementById("cvs1");
state.image = new Image();
state.image.src = 'http://www.rgraph.net/images/logo.png';
state.offsetX = 0;
state.offsetY = 0;
state.image.onload = function ()
{
Draw();
}
}
</script>
</body>
</html>
<!-- CODE COURTESY OF RICHARD HEYES OF RGRAPH
http://www.rgraph.net/blog/2013/january/an-example-of-html5-canvas-drag-n-drop.html -->
I have created the same thing on this JSFiddle but the dragging and dropping still does not work.
I am new to html5 and javascript so I am sure it must be something very simple I am overlooking, but I cannot work out what it is.
Your help with this would be much appreciated, thank you very much.
I have inserted your JavaScript code between tags <script> and </script> and move it from JavaScript to HTML and I have added new script link from the example page:
<script src="http://www.rgraph.net/libraries/RGraph.common.core.js" ></script>
JSFiddle - working example
So I think, that you must download and insert core files of RGraph to your code from this page.