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Rotate an image on top of another canvas image

Currently, I am making a game and in need of making the image rotate toward the cursor. I am using node but the image is in a js tag in the HTML file that uses ctx to draw the image.
If I put a ctx.rotate(angle); pretty much anywhere it will rotate everything; player, map, etc. I need help so that only the player is rotated
this is a simplified version of my code:
<canvas id="ctx" width="200" height="200"></canvas>
<script>
//game
var ctx = document.getElementById("ctx").getContext("2d");
var WIDTH = 200;
var HEIGHT = 200;
var Img = {};
//player
Img.player = new Image();
Img.player.src = '/client/img/player.png';
var Player = function(/*node*/){
ctx.drawImage(Img.player, ...);
}
//map
Img.map = new Image();
Img.map.src = '/client/img/map.png';
//display everything
setInterval(function(){
ctx.clearRect(0,0,200,200);
drawMap();
for(var i in Player.list)
Player.list[i].draw();
},1000/60);
//functions
//move map so that player is always in the middle
var drawMap= function(){
var x = WIDTH/2 - Player.list[/*node*/].x;
var y = HEIGHT/2 - Player.list[/*node*/].y;
ctx.drawImage(Img.map,x,y);
}
</script>

Here's an example of what you may be looking for
const ctx = document.getElementById("ctx").getContext("2d");
const WIDTH = 500,
HEIGHT = 500;
document.getElementById("ctx").height = HEIGHT;
document.getElementById("ctx").width = WIDTH;
var Player = {
x: 50,
y: 55,
angle: 0
}
document.addEventListener("mousemove", (event) => {
var x = event.clientX - Player.x,
y = event.clientY- Player.y,
angle = Math.atan2(y,x);
Player.angle = angle
})
function draw() {
window.requestAnimationFrame(draw);
ctx.clearRect(0, 0, WIDTH, HEIGHT);
ctx.save();
ctx.translate(Player.x, Player.y);
ctx.rotate(Player.angle);
ctx.translate(-Player.x, -Player.y);
ctx.fillRect(Player.x, Player.y, 20, 20);
ctx.restore();
ctx.fillRect(150, 50, 20, 20);
}
draw();
<canvas id="ctx"></canvas>
jsfiddle here
Hope this helps!

Changing Image Position drawn with canvas drawImage function [duplicate]

I am trying to move an image from the right to the center and I am not sure if this is the best way.
var imgTag = null;
var x = 0;
var y = 0;
var id;
function doCanvas()
{
var canvas = document.getElementById('icanvas');
var ctx = canvas.getContext("2d");
var imgBkg = document.getElementById('imgBkg');
imgTag = document.getElementById('imgTag');
ctx.drawImage(imgBkg, 0, 0);
x = canvas.width;
y = 40;
id = setInterval(moveImg, 0.25);
}
function moveImg()
{
if(x <= 250)
clearInterval(id);
var canvas = document.getElementById('icanvas');
var ctx = canvas.getContext("2d");
ctx.clearRect(0, 0, canvas.width, canvas.height);
var imgBkg = document.getElementById('imgBkg');
ctx.drawImage(imgBkg, 0, 0);
ctx.drawImage(imgTag, x, y);
x = x - 1;
}
Any advice?

This question is 5 years old, but since we now have requestAnimationFrame() method, here's an approach for that using vanilla JavaScript:
var imgTag = new Image(),
canvas = document.getElementById('icanvas'),
ctx = canvas.getContext("2d"),
x = canvas.width,
y = 0;
imgTag.onload = animate;
imgTag.src = "http://i.stack.imgur.com/Rk0DW.png"; // load image
function animate() {
ctx.clearRect(0, 0, canvas.width, canvas.height); // clear canvas
ctx.drawImage(imgTag, x, y); // draw image at current position
x -= 4;
if (x > 250) requestAnimationFrame(animate) // loop
}
<canvas id="icanvas" width=640 height=180></canvas>

drawImage() enables to define which part of the source image to draw on target canvas. I would suggest for each moveImg() calculate the previous image position, overwrite the previous image with that part of imgBkg, then draw the new image. Supposedly this will save some computing power.

Here's my answer.
var canvas = document.getElementById("canvas");
ctx = canvas.getContext("2d");
var myImg = new Image();
var myImgPos = {
x: 250,
y: 125,
width: 50,
height: 25
}
function draw() {
myImg.onload = function() {
ctx.drawImage(myImg, myImgPos.x, myImgPos.y, myImgPos.width, myImgPos.height);
}
myImg.src = "https://mario.wiki.gallery/images/thumb/c/cc/NSMBUD_Mariojump.png/1200px-NSMBUD_Mariojump.png";
}
function moveMyImg() {
ctx.clearRect(myImgPos.x, myImgPos.y, myImgPos.x + myImgPos.width, myImgPos.y +
myImgPos.height);
myImgPos.x -= 5;
}
setInterval(draw, 50);
setInterval(moveMyImg, 50);
<canvas id="canvas" class="canvas" width="250" height="150"></canvas>

For lag free animations,i generally use kinetic.js.
var stage = new Kinetic.Stage({
container: 'container',
width: 578,
height: 200
});
var layer = new Kinetic.Layer();
var hexagon = new Kinetic.RegularPolygon({
x: stage.width()/2,
y: stage.height()/2,
sides: 6,
radius: 70,
fill: 'red',
stroke: 'black',
strokeWidth: 4
});
layer.add(hexagon);
stage.add(layer);
var amplitude = 150;
var period = 2000;
// in ms
var centerX = stage.width()/2;
var anim = new Kinetic.Animation(function(frame) {
hexagon.setX(amplitude * Math.sin(frame.time * 2 * Math.PI / period) + centerX);
}, layer);
anim.start();
Here's the example,if you wanna take a look.
http://www.html5canvastutorials.com/kineticjs/html5-canvas-kineticjs-animate-position-tutorial/
Why i suggest this is because,setInterval or setTimeout a particular function causes issues when large amount of simultaneous animations take place,but kinetic.Animation deals with framerates more intelligently.

Explaining window.requestAnimationFrame() with an example
In the following snippet I'm using an image for the piece that is going to be animated.
I'll be honest... window.requestAnimationFrame() wasn't easy for me to understand, that is why I coded it as clear and intuitive as possible. So that you may struggle less than I did to get my head around it.
const
canvas = document.getElementById('root'),
btn = document.getElementById('btn'),
ctx = canvas.getContext('2d'),
brickImage = new Image(),
piece = {image: brickImage, x:400, y:70, width:70};
brickImage.src = "https://i.stack.imgur.com/YreH6.png";
// When btn is clicked execute start()
btn.addEventListener('click', start)
function start(){
btn.value = 'animation started'
// Start gameLoop()
brickImage.onload = window.requestAnimationFrame(gameLoop)
}
function gameLoop(){
// Clear canvas
ctx.clearRect(0, 0, canvas.width, canvas.height)
// Draw at coordinates x and y
ctx.drawImage(piece.image, piece.x, piece.y)
let pieceLeftSidePos = piece.x;
let middlePos = canvas.width/2 - piece.width/2;
// Brick stops when it gets to the middle of the canvas
if(pieceLeftSidePos > middlePos) piece.x -= 2;
window.requestAnimationFrame(gameLoop) // Needed to keep looping
}
<input id="btn" type="button" value="start" />
<p>
<canvas id="root" width="400" style="border:1px solid grey">
A key point
Inside the start() function we have:
brickImage.onload = window.requestAnimationFrame(gameLoop);
This could also be written like: window.requestAnimationFrame(gameLoop);
and it would probably work, but I'm adding the brickImage.onload to make sure that the image has loaded first. If not it could cause some issues.
Note: window.requestAnimationFrame() usually loops at 60 times per second.

Canvas background hide the rects that I added

I am new here, so please be consider.
I've created a new canvas and created a rects in the canvas , when I set a background to the canvas I have a terrible problem that The background is on the shapes
Here is the code:
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;
var background = new Image();
background.src = "url_to_image";
// Make sure the image is loaded first otherwise nothing will draw.
background.onload = function(){
ctx.drawImage(background,0,0);
}
<canvas id="canvas" width=450 height=700></canvas>
Thanks
Edit:
I found in my code a function of fillStyle that change my background,
so I delete it and instead of this I put this:
var w = canvas.width;
var h = canvas.height
var img = new Image();
img.src = "http://www.girija.info/wp-content/uploads/2015/08/Paznja-Sabranost-450x700.png";
img.onload = function () {
var pattern = ctx.createPattern(img, "repeat");
ctx.fillStyle = pattern;
ctx.fillRect(0, 0, w, h);
};
//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 = 'red';
rect(r.x, r.y, r.width, r.height);
}
But every drag of the rect (the rects loaded from stack and can be draggable) the background color of the rect change

You can set the background using the css property
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;
ctx.rect(10, 10, 100, 100);
ctx.fill();
canvas.style.backgroundImage = 'url(https://picsum.photos/450/700)';
<canvas id="canvas" width=450 height=700></canvas>

var canvas = document.getElementById('canvas'),
context = canvas.getContext('2d');
background_image();
function background_image()
{
background_image = new Image();
background_image.src = 'https://image.ibb.co/kmV8kz/photodune_2359510_smiles_l_22.png';
background_image.onload = function(){
context.drawImage(background_image, 0, 0);
}
}
<canvas id="canvas" width=450 height=700></canvas>

Drawing multiple offscreen canvases into onscreen canvas

I am having an issue when I'm trying to render multiple offscreen canvases into onscreen canvas. I do get one offscreen canvas rendered but the problem is that there should be two other rendered before. In other words, only last canvas is rendered. The expected result would be three overlapping rectangles (or squares :) in red, green and blue. Here's the code:
function rectangle(color) {
var offScreenCanvas = document.createElement('canvas');
var offScreenCtx = offScreenCanvas.getContext('2d');
var width = offScreenCanvas.width = 150;
var height = offScreenCanvas.height = 150;
switch(color) {
case 1:
offScreenCtx.fillStyle='rgb(255,0,0)';
break;
case 2:
offScreenCtx.fillStyle='rgb(0,255,0)';
break;
case 3:
offScreenCtx.fillStyle='rgb(0,0,255)';
break;
}
offScreenCtx.fillRect(0,0,width,height);
return offScreenCanvas;
}
function draw(offScreenCanvas, x , y) {
var canvas = document.getElementById('canvas')
var ctx = canvas.getContext('2d');
var width = canvas.width = window.innerWidth;
var height = canvas.height = window.innerHeight;
ctx.drawImage(offScreenCanvas, x, y);
}
var images = [];
var color = 1;
for (var i=0; i<3; i++) {
var img = new rectangle(color);
images.push(img);
color++;
}
var x = 0;
var y = 0;
for (var i = 0; i < images.length; i++) {
draw(images[i], x, y);
x += 100;
y += 100;
}
I did some searching and it seems that I'm not the first with this issue, but I could not get this working properly.

Setting canvas height or width clears the canvas.
The problem with your code is that you are causing the onscreen canvas to be cleared when you set it size in the function draw
Setting the canvas size, even if that size is the same, will cause the canvas context to reset and clear the canvas. All the other canvases are rendered, but erased when you set the onscreen canvas size.
Your draw function
function draw(offScreenCanvas, x , y) {
var canvas = document.getElementById('canvas')
var ctx = canvas.getContext('2d');
// The cause of the problem ===================================
// Either one of the following lines will clear the canvas
var width = canvas.width = window.innerWidth;
var height = canvas.height = window.innerHeight;
//=============================================================
ctx.drawImage(offScreenCanvas, x, y);
}
To avoid this just set the canvas size once. If you need to resize the canvas and keep its content you first need to create a copy of the canvas, then resize it, then render the copy back to the original.
Demo shows 5 offscreen canvases being rendered onto one onscreen canvas.
const colours = ['#f00', '#ff0', '#0f0', '#0ff', '#00f'];
const ctx = can.getContext('2d');
can.width = innerWidth - 4; // sub 4 px for border
can.height = innerHeight - 4;
function createCanvas(color, i) {
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
canvas.width = 150;
canvas.height = 150;
ctx.font = "24px arial";
ctx.fillStyle = color;
ctx.fillRect(0, i * 30, canvas.width, 30);
ctx.fillStyle = "black";
ctx.fillText("Canvas "+i,10,(i + 0.75) * 30);
return canvas;
}
colours.forEach((c, i) => {
ctx.drawImage(createCanvas(c, i), 0, 0);
})
canvas {
border: 2px solid black;
position : absolute;
top : 0px;
left : 0px;
}
<canvas id="can"></canvas>

How to select a polygonal area of an image using JavaScript / jQuery?

I'd like to be able to let my users select a specific polygonal (6-8 vertices with curved lines between points) area of an image they upload - how do I go about doing this using HTML5 & JS? The only library I found allows purely rectangular selection: http://odyniec.net/projects/imgareaselect/

There's already a library that does part of what you need: polyclip.js, by Zoltan Dulac You can build a UI that allows the user to select points, then feed the data to the library and you're done.
EDIT: Here is a jsFiddle demonstration. Click to select points on the original image and press the Generate button to generate a cropped version.
HTML:
<div id="mainContent">
<div id="canvasDiv">
<br/>
<button id="generate" type="button">Generate
</button>
</div>
<h1>Result:</h1>
<div class="clipParent" style="float:left;">
</div>
</div>
JS:
var canvasDiv = document.getElementById('canvasDiv');
canvas = document.createElement('canvas');
canvas.setAttribute('width', 500);
canvas.setAttribute('height', 500);
canvas.setAttribute('id', 'canvas');
$(canvasDiv).prepend(canvas);
if(typeof G_vmlCanvasManager != 'undefined') {
canvas = G_vmlCanvasManager.initElement(canvas);
}
var context = canvas.getContext('2d');
var imageObj = new Image();
imageObj.onload = function() {
$(canvas).attr({width : this.width, height: this.height});
context.drawImage(imageObj,0,0);
};
imageObj.src = 'http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg';
var clickX = new Array();
var clickY = new Array();
var clickDrag = new Array();
var paint;
function addClick(x, y, dragging)
{
clickX.push(x);
clickY.push(y);
clickDrag.push(dragging);
}
function redraw(){
canvas.width = canvas.width; // Clears the canvas
context.drawImage(imageObj,0,0);
context.strokeStyle = "#df4b26";
context.lineJoin = "round";
context.lineWidth = 5;
for(var i=0; i < clickX.length; i++)
{
context.beginPath();
context.arc(clickX[i], clickY[i], 3, 0, 2 * Math.PI, false);
context.fillStyle = '#ffffff';
context.fill();
context.lineWidth = 5;
context.stroke();
}
}
$('#canvas').click(function(e){
var mouseX = e.pageX - this.offsetLeft;
var mouseY = e.pageY - this.offsetTop;
addClick(e.pageX - this.offsetLeft, e.pageY - this.offsetTop);
redraw();
});
$('#generate').click(function(){
$(".clipParent").empty();
$(".clipParent").prepend('<img src="http://www.html5canvastutorials.com/demos/assets/darth-vader.jpg" id="genimg" />');
var arr = [];
for(var i=0; i < clickX.length; i++){
arr.push(clickX[i]);
arr.push(clickY[i]);
}
$("#genimg")[0].setAttribute("data-polyclip",arr.join(", "));
clickX=[];
clickY=[];
redraw();
polyClip.init();
});

You could load the image on to a canvas tag and then you can do all the drawing you like on that canvas.