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javascript ImageData copy or move performance

I am writing a "waterfall" diagram for an SDR receiver which is displayed in a canvas on a web page.
The canvas has a size of w=1000 h=800 pixels.
The top line is delivered every 50ms from a server.
The browser (using javascript) must move all lines down one line and then insert the new line at the top. This gives the look of a waterfall where all pixels are moving from top to bottom.
It is working fine, but the CPU load for the pixel moving is very high, too high for i.e. a raspberry.
What I am doing is:
var imagedata = context.getImageData(0,0,pixwidth,height-1);
var dataCopy = new Uint8ClampedArray(imagedata.data);
for(i=(dataCopy.length - (2*pixwidth*4)); i>= 0; i--) {
dataCopy[i+ pixwidth*4] = dataCopy[i];
}
imagedata.data.set(dataCopy);
// insert new top line
// ....
context.putImageData(imagedata, 0, 0);
I also tried to directly copy the pixel data in imagedata[some index],
which gives almost the same bad performance.
In another C-Program I did the same thing with a simple memcpy operation which is very fast. But what to do in Javascript ?
There are 800.000 pixels, which are 3.200.000 bytes. How can I copy or move them with the best possible performance in Javascript ?

var cv = document.getElementById('cv');
var ctx = cv.getContext('2d');
function draw() {
ctx.fillStyle = `hsla(${360 * Math.random()}, 100%, 50%, 1)`;
ctx.fillRect(0, 0, cv.width, 10);
ctx.drawImage(cv, 0, 10);
}
setInterval(function() { draw() }, 200)
<canvas id="cv" width="800" height="400"></canvas>
After drawing a line, take a snapshot of the entire canvas and redraw it with an offset of 10 px on the y scale. Repeat the process and you will get an waterfall like effect.

How to make the effect of moving the image in the window canvas?

For example I have a limited canvas, smaller width/height than the uploaded image in it.
Guys how to make the effect of moving the image in the canvas window? In other words, the canvas window does not change, and the picture we "run". thanks

Animation basic movement
Like all animation to make something appear as if it moves is to draw a sequence of still images (a frame), each image slightly different. If the rate of frames are high enough (over about 20 per second) the human eye and mind see the sequence of still images as a continuous movement. From the first movies to today's high end games this is how animation is done.
So for the canvas the process of drawing a frame is simple. Create a function that clears the canvas, draws what you need, exit the function so that the browser can move the completed frame to the display. (Note that while in the function anything draw on the canvas is not seen on the display, you must exit the function to see what is drawn)
To animate you must do the above at at least more than 20 times a seconds. For the best results you should do it at the same rate as the display hardware shows frames. For the browser that is always 60 frames per second (fps).
Animation in the browser
To help sync with the display you use the function requestAnimationFrame(myDrawFunction) it tells the browser that you are animating, and that the results of the rendering should be displayed only when the display hardware is ready to show a new complete frame, not when the draw function has exited (which may be halfway through a hardware frame).
Animation Object
So as a simple example let's create a animation object.
const imageSrc = "https://i.stack.imgur.com/C7qq2.png?s=328&g=1";
const myImage = {
posX: 0, // current position of object
posY: 0,
speed: 3, // speed in pixels per frame (1/60th second)
direction: 0, // direction of movement in radians 0 is at 3oclock
image: (() => { // create and load an image (Image will take time to load
// and may not be ready until after the code has run.
const image = new Image;
image.src = imageSrc;
})(),
Draw function
Then a draw function that draws the object on the canvas
draw(ctx) {
ctx.drawImage(this.image, this.posX, this.posY);
},
Update function
As we are animating we need to move the object once per frame, to do this we create a update function.
update() {
this.posX += (mx = Math.cos(this.direction)) * this.speed;
this.posY += (my = Math.sin(this.direction)) * this.speed;
}
} // end of object
Many times a second
To do the animation we create a main loop that is call for every hardware display frame via requestAnimationFrame.
function mainLoop() {
// clear the canvas
ctx.clearRect(0, 0, canvas.width, canvas.height);
// update the obj
myImage.update();
// draw the object
myImage.draw(ctx);
// request the next frame
requestAnimationFrame(mainLoop);
// note all of the above code is not seen by the use until the
// next hardwares display frame. If you used setTimeout or setInterval
// then it would be displayed when this function exits (which may be
// halfway through a frame resulting in the animation being cut in two)
}
// request the first frame
requestAnimationFrame(mainLoop);
Some extras
And that is the most basic animation. of course you need to get the canvas context and wait for the image to load. Also because the image moves of the canvas you would need to check when it does and either stop the animation.
Eg to stop animation is image is off screen
if(myImage.posX < canvas.width){ // only render while image is on the canvas
requestAnimationFrame(mainLoop);
} else {
console.log("Animation has ended");
}
Now to put it together as a demo.
The demo
The demo has some extra smarts to make the image wrap around, ensure that the image has loaded before starting and make it start off screen, but is basicly the same as outlined above.
// get the 2D context from the canvas id
const ctx = canvas.getContext("2d");
// setup the font and text rendering
ctx.font = "32px arial";
ctx.textAlign = "center";
ctx.textBaseline = "middle";
// create the image object and load the image
const imageSrc = "https://i.stack.imgur.com/C7qq2.png?s=328&g=1";
const myImage = {
posX: 0, // current position of object
posY: 0,
speed: 3, // speed in pixels per frame (1/60th second)
direction: 0, // direction of movement in radians 0 is at 3oclock
image: (() => { // create and load an image (Image will take time to load
// and may not be ready until after the code has run.
const image = new Image;
image.src = imageSrc;
// to start move the image of the display
image.onload = function(){
const imageDiagonalSize = Math.sqrt(
image.width * image.width + image.height * image.height
)
myImage.posX = (canvas.width / 2) - imageDiagonalSize - Math.cos(myImage.direction) * imageDiagonalSize;
myImage.posX = (canvas.height / 2) - imageDiagonalSize - Math.sin(myImage.direction) * imageDiagonalSize;
}
return image;
})(),
draw(ctx) {
ctx.drawImage(this.image, this.posX, this.posY);
},
update() {
var mx,my; // get movement x and y
this.posX += (mx = Math.cos(this.direction)) * this.speed;
this.posY += (my = Math.sin(this.direction)) * this.speed;
// if the image moves of the screen move it to the other side
if(mx > 0) { // if moving right
if(this.posX > canvas.width){
this.posX = 0-this.image.width;
}
}else if(mx < 0) { // if moving left
if(this.posX + this.image.width < 0){
this.posX = canvas.width;
}
}
if(my > 0) { // if moving down
if(this.posY > canvas.height){
this.posY = 0-this.image.height;
}
}else if(my < 0) { // if moving up
if(this.posY + this.image.height < 0){
this.posY = canvas.height;
}
}
}
}
function mainLoop() {
// clear the canvas
ctx.clearRect(0, 0, canvas.width, canvas.height);
if(myImage.image.complete) { // wait for image to load
myImage.update();
myImage.draw(ctx);
}else{ // some feedback to say the image is loading
ctx.fillText("Loading image..",canvas.width / 2, canvas.height / 2);
}
// request the next frame
requestAnimationFrame(mainLoop);
}
// request the first frame
requestAnimationFrame(mainLoop);
canvas {
border: 2px solid black;
}
<!-- id's must be unique to the page -->
<canvas id="canvas"></canvas>
Please note that the above code uses ES6 and will need a code pre processor like Babel to run on legacy browsers.

Check out this answer: https://stackoverflow.com/a/30739547/3200577
Basically, the way that html canvas works is very different from how html elements are rendered and painted. Whereas you can select and move an html element on the page, you cannot select and move something that you have added to a canvas because all you can do on a canvas is add and clear pixels. So, when you add an image to a canvas, you are adding the pixels of the image to the canvas. If you were to add the image again but a little to the left, then it would look like you've added two images, where the second one overlaps the first, which is not what you want.
So, to animate the motion of an image on the canvas, you need to:
choose an x and y as the position of the image on the canvas
draw the image on the canvas at x and y
increment the values of x and y to the new position that you want
clear the canvas
redraw the image at the new x and y
A more abstract description of this flow: basically, you need to create, store, and manage your own model of what your canvas looks like; when you want to add, remove of change things that you've painted on the canvas, you actually aren't going to be adding, removing, or changing anything directly on the canvas. You would add, remove and change things in your own model, clear the canvas, and then redraw the canvas on the basis of your model.
For instance, your model might be a JS object such as
myModel = {
images: [
{ url: "my/picture.png", position: [123,556] },
{ url: "another/picture.jpg", position: [95,111] }
]
}
and you would write functions for 1) incrementing the values of the positions of the images in the model, 2) clearing the canvas, and 3) drawing your model onto the canvas. Then, you would create a loop (using requestAnimationFrame or setInterval) that would repeatedly execute those three functions.
For large or complex projects, I strongly recommend using a canvas library such as paperjs, which implements that flow for you (so that you don't have to think about creating a model and clearing and redrawing the canvas). It provides high-level functionality such as animation right out of the box.

Why wont my sprite appear on top of my background?

I have been practicing using sprites for a game I am going to make and have watched and read a few tutorials, I thought I was close to getting my sprite to appear so I could finally start my game but while practicing I cant get it to work, I have dont 2 seperate tutorials where I can get the sprite and the background to appear by themselfs but cannot get them to work together, I have been using EaselJS too. some of the sprite animation code has been copied from tutorials too.
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8">
<title>sprite prac<title>
<!-- EaselJS library -->
<script src="lib/easel.js"></script>
<script>
// Initialize on start up so game runs smoothly
function init() {
canvas = document.getElementById("canvas");
stage = new Stage(canvas);
bg = new Image();
bg.src = "img/grassbg.jpg";
bg.onload = setBG;
stage.addChild(background);
imgMonsterARun = new Image();
imgMonsterARun.onload = handleImageLoad;
imgMonsterARun.onerror = handleImageError;
imgMonsterARun.src = "img/MonsterARun.png";
stage.update();
}
function handleImageLoad(e) {
startGame();
}
// Simple function for setting up the background
function setBG(event){
var bgrnd = new Bitmap(bg);
stage.addChild(bgrnd);
stage.update();
}
function startGame() {
// create a new stage and point it at our canvas:
stage = new createjs.Stage(canvas);
// grab canvas width and height for later calculations:
screen_width = canvas.width;
screen_height = canvas.height;
// create spritesheet and assign the associated data.
var spriteSheet = new createjs.SpriteSheet({
// image to use
images: [imgMonsterARun],
// width, height & registration point of each sprite
frames: {width: 64, height: 64, regX: 32, regY: 32},
animations: {
walk: [0, 9, "walk"]
}
});
// create a BitmapAnimation instance to display and play back the sprite sheet:
bmpAnimation = new createjs.BitmapAnimation(spriteSheet);
// start playing the first sequence:
bmpAnimation.gotoAndPlay("walk"); //animate
// set up a shadow. Note that shadows are ridiculously expensive. You could display hundreds
// of animated rats if you disabled the shadow.
bmpAnimation.shadow = new createjs.Shadow("#454", 0, 5, 4);
bmpAnimation.name = "monster1";
bmpAnimation.direction = 90;
bmpAnimation.vX = 4;
bmpAnimation.x = 16;
bmpAnimation.y = 32;
// have each monster start at a specific frame
bmpAnimation.currentFrame = 0;
stage.addChild(bmpAnimation);
// we want to do some work before we update the canvas,
// otherwise we could use Ticker.addListener(stage);
createjs.Ticker.addListener(window);
createjs.Ticker.useRAF = true;
createjs.Ticker.setFPS(60);
}
//called if there is an error loading the image (usually due to a 404)
function handleImageError(e) {
console.log("Error Loading Image : " + e.target.src);
}
function tick() {
// Hit testing the screen width, otherwise our sprite would disappear
if (bmpAnimation.x >= screen_width - 16) {
// We've reached the right side of our screen
// We need to walk left now to go back to our initial position
bmpAnimation.direction = -90;
}
if (bmpAnimation.x < 16) {
// We've reached the left side of our screen
// We need to walk right now
bmpAnimation.direction = 90;
}
// Moving the sprite based on the direction & the speed
if (bmpAnimation.direction == 90) {
bmpAnimation.x += bmpAnimation.vX;
}
else {
bmpAnimation.x -= bmpAnimation.vX;
}
// update the stage:
stage.update();
}
</script>
</head>
<body onload="init();">
<canvas id="canvas" width="500" height="500" style="border: thin black solid;" ></canvas>
</body>
</html>

There are a few places where you are using some really old APIs, which may or may not be supported depending on your version of EaselJS. Where did you get the easel.js script you reference?
Assuming you have a version of EaselJS that matches the APIs you are using, there are a few issues:
You add background to the stage. There is no background, so you are probably getting an error when you add it. You already add bgrnd in the setBackground method, which should be fine. If you get an error here, then this could be your main issue.
You don't need to update the stage any time you add something, just when you want the stage to "refresh". In your code, you update after setting the background, and again immediately at the end of your init(). These will fire one after the other.
Are you getting errors in your console? That would be a good place to start debugging. I would also recommend posting code if you can to show an actual demo if you continue to have issues, which will help identify what is happening.
If you have a newer version of EaselJS:
BitmapAnimation is now Sprite, and doesn't support direction. To flip Sprites, use scaleX=-1
Ticker no longer uses addListener. Instead it uses the EventDispatcher. createjs.Ticker.addEventListener("tick", tickFunction);
You can get new versions of the CreateJS libraries at http://code.createjs.com, and you can get updated examples and code on the website and GitHub.

Canvas generated by canvg is blurry on retina screen

I'm using Raphael to draw an object, then transferring it to an HTML canvas element with canvg so that I can use toDataURL to save it as a PNG. But when I use canvg, the resulting image is blurry. The code below, for example, produces this (raphael on top, canvg on bottom):
<html>
<head>
<script src="lib/raphael-min.js"></script>
<script type="text/javascript" src="http://canvg.googlecode.com/svn/trunk/rgbcolor.js"></script>
<script type="text/javascript" src="http://canvg.googlecode.com/svn/trunk/StackBlur.js"></script>
<script type="text/javascript" src="http://canvg.googlecode.com/svn/trunk/canvg.js"></script>
<script src="lib/raphael.export.js"></script>
</head>
<body>
<div id="raph_canvas"></div><br>
<canvas id="html_canvas" width="50px" height="50px"></canvas>
<script language="JavaScript">
var test=Raphael("raph_canvas",50,50);
var rect=test.rect(0,0,50,50);
rect.attr({fill: '#fff000', 'fill-opacity':1, 'stroke-width':1})
window.onload = function() {
var canvas_svg = test.toSVG();
canvg('html_canvas',canvas_svg);
var canvas_html = document.getElementById("html_canvas");
}
</script>
</body>
</html>
The blurriness is evident in the png created by toDataURL as well. Any idea what is going on here? I don't think this has anything to do with re-sizing. I've tried setting ignoreDimensions: True and some other things.
Another datapoint. If I use raphael to output some text and then use canvg, it is not only blurry but the wrong font!
And here is the test.rect(0.5,0.5,50,50) suggested. Still blurry:

So it took me a while, but then it dawned on me. All your example images are twice the size the code claims they should be. So you're most likely on some sort of HDPI device (Retina MacBook Pro ect...) SVG is great because its resolution independent, canvas on the other hand is not. The issue you're seeing has to do with how canvas renders. To fix this, you need to prep the canvas so that your drawing will be done at the resolution of your screen.
http://jsbin.com/liquxiyi/3/edit?html,js,output
This jsbin example should look great on any screen.
The trick:
var cv = document.getElementById('box');
var ctx = cv.getContext("2d");
// SVG is resolution independent. Canvas is not. We need to make our canvas
// High Resolution.
// lets get the resolution of our device.
var pixelRatio = window.devicePixelRatio || 1;
// lets scale the canvas and change its CSS width/height to make it high res.
cv.style.width = cv.width +'px';
cv.style.height = cv.height +'px';
cv.width *= pixelRatio;
cv.height *= pixelRatio;
// Now that its high res we need to compensate so our images can be drawn as
//normal, by scaling everything up by the pixelRatio.
ctx.setTransform(pixelRatio,0,0,pixelRatio,0,0);
// lets draw a box
// or in your case some parsed SVG
ctx.strokeRect(20.5,20.5,80,80);
// lets convert that into a dataURL
var ur = cv.toDataURL();
// result should look exactly like the canvas when using PNG (default)
var result = document.getElementById('result');
result.src=ur;
// we need our image to match the resolution of the canvas
result.style.width = cv.style.width;
result.style.height = cv.style.height;
This should explain the issue you're having, and hopefully point you in a good direction to fix it.

Another solution described in this article, similar to the one posted here, except it's using scale() and it's taking into account the pixel ratio of the backing store (browser underlying storage of the canvas):
var devicePixelRatio = window.devicePixelRatio || 1,
backingStoreRatio = context.webkitBackingStorePixelRatio ||
context.mozBackingStorePixelRatio ||
context.msBackingStorePixelRatio ||
context.oBackingStorePixelRatio ||
context.backingStorePixelRatio || 1,
ratio = devicePixelRatio / backingStoreRatio;
// upscale the canvas if the two ratios don't match
if(devicePixelRatio !== backingStoreRatio){
// adjust the original width and height of the canvas
canvas.width = originalWidth * ratio;
canvas.height = originalHeight * ratio;
// scale the context to reflect the changes above
context.scale(ratio, ratio);
}
// ...do the drawing here...
// use CSS to bring the entire thing back to the original size
canvas.style.width = originalWidth + 'px';
canvas.style.height = originalHeight + 'px';

Error in JavaScript on Canvas(HTML5)- can't figure it out

I have JavaScript code in my site.
The code is using 2 identical photos-same size, same resolution - only different colors.
First photo is black and white photo - this is what the canvas presents.
Second photo is the same only with the original colors.
I have a button that triggers JS code - which generally removes a pixel from the black and white -and paints color pixel on the canvas. At first I used Math.random for the pixel locations.
And than I decided to use it by order. No matter where it starts or begging.. as long it will go
in this order (x,y)..(x+1,y).. until maximum x.. and than (x,y+1).. until maximum x.. and so on until all the black and white photo "transformed" into the colorful photo..
for some reason I just cant make it happen.. i tried a lot of techniques..
here is demo for global understanding:
demo is working sorry - they deactivated my free host :\ hope you still understand..
here is the original code- i just changed the last function : **removeDrawRandomPixel** ..it's just playing the function there and it should be fixed..
///////////////////////global variables///////////////////
var gray_url="bwcat.jpg"; //black and white image URI
var regular_url="cat.jpg"; //regular image URI
var n=100; //number of pixels changed per click
/////////////////////////////////////
document.addEventListener("DOMContentLoaded", function(){
var c=new EditableCanvas(document.getElementById('cnvs'));
grayScaleImage=new Image();
grayScaleImage.src=gray_url;
grayScaleImage.onload=function()
{
c.drawImage(this);
}
regularImage=new Image();
regularImage.src=regular_url;
regularImage.onload=function()
{
var p=getPixelArray(this);
btn.onclick=function(){
for(var i=1;i<=n&&p.length>0;i++){
removeDrawRandomPixel(p,c);
}
}
}
},false);
//create a Pixel object
function ImagePixel(x,y,r,g,b,a)
{
this.x=x;
this.y=y;
this.r=r;
this.g=g;
this.b=b;
this.a=a;
}
//object that allows custom methods
function EditableCanvas(canvas)
{
this.canvas=canvas;
this.context=canvas.getContext('2d');
this.width=canvas.width;
this.height=canvas.height;
this.pixelImage=this.context.createImageData(1,1);
//draw an entire picture and adjust the canvas for it
this.drawImage=function(image)
{
this.width=image.width;
this.height=image.height;
this.canvas.height=image.height;
this.canvas.width=image.width;
this.context.drawImage(image,0,0);
}
//draw a single pixel, ImagePixel pixel
this.drawPixel=function(pixel)
{
this.pixelImage.data[0]=pixel.r;
this.pixelImage.data[1]=pixel.g;
this.pixelImage.data[2]=pixel.b;
this.pixelImage.data[3]=pixel.a;
this.context.putImageData(this.pixelImage,pixel.x,pixel.y);//,pixel.x,pixel.y);
}
}
//the function returns an ordered array of Pixel pixels of the image at `src`.
function getPixelArray(img)
{
var pixelArray=[];
var cnvs=document.createElement('canvas');
cnvs.width=img.width;
cnvs.height=img.width;
var context=cnvs.getContext('2d');
context.drawImage(img,0,0);
var originalData = context.getImageData(0,0,img.width,img.height).data;
for(var i=0,pixelId=0,px;i<originalData.length;i+=4)
{
px=new ImagePixel(pixelId%img.width,Math.floor(pixelId/img.width),originalData[i],originalData[i+1],originalData[i+2],originalData[i+3]);
pixelArray.push(px);
pixelId++;
}
return pixelArray;
}
//the function remove a random pixel from pixelArray and draws it on editableCnvs
function removeDrawRandomPixel(pixelArray,editableCnvs)
{
var place=Math.floor(Math.random()*pixelArray.length);
var px=pixelArray.splice(place,1)[0];
editableCnvs.drawPixel(px);
}
html :
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>canvas rules</title>
<script src="pixel.js"></script>
</head>
<body>
<canvas id="cnvs">
oh goddmamit no support
</canvas>
<button id="btn">click to convert</button>
</body>
</html>
I tried playing the last function.. because i know the answer is in the function,how to choose the pixels..

This is untested however this is what I would change the removeDrawRandomPixel function to. You are grabbing a random point in the array currently and passing it, so it could be starting on the blue component of one pixel and ending on the g component of another pixel.
//the function remove a random pixel from pixelArray and draws it on editableCnvs
function removeDrawRandomPixel(pixelArray,editableCnvs)
{
// width and height need to be the width and height of the canvas.
var width = canvas.width,
height = canvas.height,
x = Math.floor(Math.random()*width),
y = Math.floo(Math.random()*height);
var px = (y * width + x) * 4;
editableCnvs.drawPixel(px);
}