Strange 700ms delay when using context.drawImage(); - javascript

I'm working on a small canvas animation that requires me to step through a large sprite sheet png so I'm getting a lot of mileage out of drawImage(). I've never had trouble in the past using it, but today I'm running into an odd blocking delay after firing drawImage.
My understanding is that drawImage is synchronous, but when I run this code drawImage fired! comes about 700ms before the image actually appears. It's worth noting it's 700ms in Chrome and 1100ms in Firefox.
window.addEventListener('load', e => {
console.log("page loaded");
let canvas = document.getElementById('pcb');
let context = canvas.getContext("2d");
let img = new Image();
img.onload = function() {
context.drawImage(
img,
800, 0,
800, 800,
0, 0,
800, 800
);
console.log("drawImage fired!");
};
img.src = "/i/sprite-comp.png";
});
In the larger context this code runs in a requestAnimationFrame loop and I only experience this delay during the first execution of drawImage.
I think this is related to the large size of my sprite sheet (28000 × 3200) # 600kb though the onload event seems to be firing correctly.
edit: Here's a printout of the time (ms) between rAF frames. I get this result consistently unless I remove the drawImage function.

That's because the load event only is a network event. It only tells that the browser has fetched the media, parsed the metadata, and has recognized it is a valid media file it can decode.
However, the rendering part may still not have been made when this event fires, and that's why you have a first rendering that takes so much time. (Though it used to be an FF only behavior..)
Because yes drawImage() is synchronous, It will thus make that decoding + rendering a synchrounous operation too. It's so true, that you can even use drawImage as a way to tell when an image really is ready..
Note that there is now a decode() method on the HTMLImageElement interface that will tell us exactly about this, in a non-blocking means, so it's better to use it when available, and to anyway perform warming rounds of all your functions off-screen before running an extensive graphic app.
But since your source image is a sprite-sheet, you might actually be more interested in the createImageBitmap() method, which will generate an ImageBitmap from your source image, optionally cut off. These ImageBitmaps are already decoded and can be drawn to the canvas with no delay. It should be your preferred way since it will also avoid that you draw the whole sprite-sheet every time. And for browsers that don't support this method, you can monkey patch it by returning an HTMLCanvasElement with the part of the image drawn on it:
if (typeof window.createImageBitmap !== "function") {
window.createImageBitmap = monkeyPatch;
}
var img = new Image();
img.crossOrigin = "anonymous";
img.src = "https://upload.wikimedia.org/wikipedia/commons/b/be/SpriteSheet.png";
img.onload = function() {
makeSprites()
.then(draw);
};
function makeSprites() {
var coords = [],
x, y;
for (y = 0; y < 3; y++) {
for (x = 0; x < 4; x++) {
coords.push([x * 132, y * 97, 132, 97]);
}
}
return Promise.all(coords.map(function(opts) {
return createImageBitmap.apply(window, [img].concat(opts));
})
);
}
function draw(sprites) {
var delay = 96;
var current = 0,
lastTime = performance.now(),
ctx = document.getElementById('canvas').getContext('2d');
anim();
function anim(t) {
requestAnimationFrame(anim);
if (t - lastTime < delay) return;
lastTime = t;
current = (current + 1) % sprites.length;
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height)
ctx.drawImage(sprites[current], 0, 0);
}
}
function monkeyPatch(source, sx, sy, sw, sh) {
return Promise.resolve()
.then(drawImage);
function drawImage() {
var canvas = document.createElement('canvas');
canvas.width = sw || source.naturalWidth || source.videoWidth || source.width;
canvas.height = sh || source.naturalHeight || source.videoHeight || source.height;
canvas.getContext('2d').drawImage(source,
sx || 0, sy || 0, canvas.width, canvas.height,
0, 0, canvas.width, canvas.height
);
return canvas;
}
}
<canvas id="canvas" width="132" height="97"></canvas>

Related

p5.js | Quality of image captured from camera feed, lower than actual camera feed?

With the code below, the quality of the video coming from my Mac's camera and shown inside <video> is great.
However the quality of the frame I capture and show in p5's canvas is pretty low, dark and grainy. Why is that and can I fix it ?
function setup() {
let canvas = createCanvas(canvasSize, canvasSize)
canvas.elt.width = canvasSize
canvas.elt.height = canvasSize
video = createCapture(VIDEO)
}
let PAUSE = false
async function draw() {
if (video && video.loadedmetadata) {
if (!PAUSE) {
// the quality of this image is much lower than what is shown inside p5's <video>
image(video.get(), 0, 0, canvasSize, canvasSize, x, y, canvasSize, canvasSize)
PAUSE = true
}
}
}
I found what the problem was.
It was not due to me setting the canvas.elt.width and canvas.elt.height, even though setting them is indeed redundant.
It's because in the code shown in the OP I was capturing the very first frame and this is too soon so the very first frame is still dark and blurry. Apparently the first few frames coming from the camera are like that.
If I give my code a delay of e.g. 5 seconds the frame it captures is then the exact same quality as the one coming from the video feed.
let video
let canvasWidth = 400
// set this to 10 on https://editor.p5js.org/ and you'll see the problem
const DELAY = 5000
function setup() {
let canvas = createCanvas(canvasWidth, canvasWidth)
canvas.elt.width = canvasWidth // redundant
canvas.elt.height = canvasWidth // redundant
video = createCapture(VIDEO)
}
let PAUSE = false
let start = Date.now()
async function draw() {
let delay = Date.now() - start
if (video && video.loadedmetadata) {
if (delay > DELAY && !PAUSE) {
PAUSE = true
let x = Math.round((video.width / 2) - (canvasWidth / 2))
let y = Math.round((video.height / 2) - (canvasWidth / 2))
// the quality of this image is now perfect
image(video.get(), 0, 0, canvasWidth, canvasWidth, x, y, canvasWidth, canvasWidth)
}
}
}
You should not be setting width/height this way. That will mess up the sizing on high DPI displays and cause your image to appear stretched and blurry.
const canvasSize = 500;
function setup() {
let canvas = createCanvas(canvasSize, canvasSize)
// Don't do this, it will mess up the sizing on high DPI displays:
// canvas.elt.width = canvasSize
// canvas.elt.height = canvasSize
video = createCapture(VIDEO)
}
let PAUSE = false;
function draw() {
if (video && video.loadedmetadata) {
if (!PAUSE) {
// the quality of this image is much lower than what is shown inside p5's <video>
image(video.get(), 0, 0, canvasSize, canvasSize, 0, 0, canvasSize, canvasSize)
}
}
}
function keyPressed() {
if (key === 'p') {
PAUSE = !PAUSE;
}
}
With this code I paused the video that was being rendered to p5.js and then took a screenshot. The version of the video displayed on the p5.js canvas wash indistinguishable from the live video.

Recording speed javascript

I am currently creating a project that supports video recording through my website.
I create a canvas and then push the recorded frames to it. The problem is, when I play the video after its recorded, it plays too fast. A 10 second long video plays in like 2 seconds. I have checked the playbackRate is set to 1. I save the recording to a database and its speeded up there aswell, so it has nothing to do with the browsers videoplayer.
I am relative new to AngularJS and javascript so im sorry if I left something important out.
I have tried changing alot of the values back and forth but I cant seem to find the cause for the problem. Any ideas?
Here is the code for the video recording:
scope.startRecording = function () {
if (mediaStream) {
var video = $('.video-capture')[0];
var canvas = document.createElement('canvas');
canvas.height = video.videoHeight;
canvas.width = video.videoWidth;
ctx = canvas.getContext('2d');
var CANVAS_WIDTH = canvas.width;
var CANVAS_HEIGHT = canvas.height;
function drawVideoFrame(time) {
videoRecorder = requestAnimationFrame(drawVideoFrame);
ctx.drawImage(video, 0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
recordedFrames.push(canvas.toDataURL('image/webp', 1));
}
videoRecorder = requestAnimationFrame(drawVideoFrame); // Note: not using vendor prefixes!
scope.recording = true;
}
};
scope.stopRecording = function () {
cancelAnimationFrame(videoRecorder); // Note: not using vendor prefixes!
// 2nd param: framerate for the video file.
scope.video.files = Whammy.fromImageArray(recordedFrames, 1000 / 30);
recordedVideoBlob = Whammy.fromImageArray(recordedFrames, 1000 / 30);
scope.videoMode = 'viewRecording';
scope.recording = false;
};
I am guess the culprit is requestAnimationFrame, left on it's own, you cannot tell at what intervals it keeps calling the callback, it can be as high as 60fps.
also looking at your code, I cannot tell how you came to the conclusion that frame rate = 1000/30
my advice( at least for your case) would be to go with $interval,
you can do something like:
scope.frameRate = 10, videoInterval; // the amount I consider ideal for client-side video recording.
scope.startRecording = function () {
if (mediaStream) {
var video = $('.video-capture')[0];
var canvas = document.createElement('canvas');
canvas.height = video.videoHeight;
canvas.width = video.videoWidth;
ctx = canvas.getContext('2d');
var CANVAS_WIDTH = canvas.width;
var CANVAS_HEIGHT = canvas.height;
function drawVideoFrame() {
ctx.drawImage(video, 0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
recordedFrames.push(canvas.toDataURL('image/webp', 1));
}
videoInterval = $interval(drawVideoFrame, 1000/scope.frameRate);
scope.recording = true;
}
};
scope.stopRecording = function () {
$interval.cancel(videoInterval);
// 2nd param: framerate for the video file.
scope.video.files = Whammy.fromImageArray(recordedFrames, scope.frameRate);
recordedVideoBlob = Whammy.fromImageArray(recordedFrames, scope.frameRate); // you can chage this to some file copy method, so leave out the duplicate processing of images into video.
scope.videoMode = 'viewRecording';
scope.recording = false;
};

JavaScript - how to draw on the canvas and get an image to follow the mouse

I've gotten a lot of help from this site, but I seem to be having a problem putting all of it together. Specifically, in JS, I know how to
a) draw an image onto canvas
b) make a rectangle follow the cursor (Drawing on a canvas) and (http://billmill.org/static/canvastutorial/ball.html)
c) draw a rectangle to use as a background
What I can't figure out is how to use a rectangle as the background, and then draw an image (png) on the canvas and get it to follow the cursor.
What I have so far looks like this:
var canvas = document.getElementByID('canvas');
var ctx = canvas.getContext('2d');
var WIDTH = canvas.width;
var HEIGHT = canvas.height;
var bgColor = '#FFFFFF';
var cirColor = '#000000';
clear = function() {
ctx.clearRect(0, 0, WIDTH, HEIGHT);
}
drawIMG = function(x,y,r) {
ctx.fillStyle = cirColor;
ctx.beginPath();
ctx.arc(x, y, r, 0, Math.PI*2, true);
ctx.closePath();
ctx.fill();
}
draw = function() {
ctx.fillStyle = bgColor;
clear();
ctx.fillRect(0, 0, WIDTH, HEIGHT);
drawIMG(150, 150, 30);
drawIMG(300, 500, 12);
};
draw();
This will draw in the HTML5 canvas element, the height and width of which are specified in the HTML and so are variable, with a white rectangle the size of the canvas beneath two black circles at (150,150) and (300,500). It does that perfectly well.
However, I don't know how to also make JS draw a .png on top of that that follows the cursor. Like I said, I've been able to do most of the steps individually, but I have no idea how to combine them. I know, for instance, that I have to do
img = new Image();
and then
img.src = 'myPic.png';
at some point. They need to be combined with position modifiers like
var xPos = pos.clientX;
var yPos = pos.clientY;
ctx.drawImage(img, xPos, yPos);
But I have no idea how to do that while maintaining any of the other things I've written above (specifically the background).
Thanks for your patience if you read through all of that. I have been up for a while and I'm afraid my brain is so fried I wouldn't recognize the answer if it stripped naked and did the Macarena. I would appreciate any help you could possibly send my way, but I think a working example would be best. I am an initiate in the religion of programming and still learn best by shamelessly copying and then modifying.
Either way, you have my optimistic thanks in advance.
First off, I've made an animated purple fire follow the mouse. Click (edit doesn't exist anymore)here to check it out.
Before you continue, I recommend you check out these websites:
http://www.williammalone.com/articles/create-html5-canvas-javascript-sprite-animation/
William talks about the basic techniques of canvas animations
http://www.paulirish.com/2011/requestanimationframe-for-smart-animating/
Paul Irish talks about a recursive animation function that turns at 60 fps.
Using both of their tutorials is pretty a good start for animation.
Now from my understanding you want one 'background' and one animation that follows the cursor. The first thing you should keep in mind is once you draw on your canvas, whatever you draw on, gets replaced. So the first thing I notice that will cause performance issues is the fact you clear your whole canvas, and not what needs to be cleared.
What you need to do is memorize the position and size of your moving element. It doesn't matter what form it takes because your clearRect() should completely remove it.
Now you're probably asking, what if I draw on the rectangle in the background. Well that will cause a problem. You have two solutions. Either, (a) Clear the background and clear your moving animation and draw them back again in the same order or (b) since you know your background will never move, create a second canvas with position = absolute , z-index = -1 , and it's location the same as the first canvas.
This way you never have to worry about the background and can focus on the animation currently going on.
Now getting back to coding part, the first thing you'll want to do is copy Paul Irish's recursive function:
(function() {
var lastTime = 0;
var vendors = ['webkit', 'moz'];
for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
window.requestAnimationFrame = window[vendors[x]+'RequestAnimationFrame'];
window.cancelAnimationFrame =
window[vendors[x]+'CancelAnimationFrame'] || window[vendors[x]+'CancelRequestAnimationFrame'];
}
if (!window.requestAnimationFrame)
window.requestAnimationFrame = function(callback, element) {
var currTime = new Date().getTime();
var timeToCall = Math.max(0, 16 - (currTime - lastTime));
var id = window.setTimeout(function() { callback(currTime + timeToCall); },
timeToCall);
lastTime = currTime + timeToCall;
return id;
};
if (!window.cancelAnimationFrame)
window.cancelAnimationFrame = function(id) {
clearTimeout(id);
};
}());
Question then is, how to use it? If you go here you can check out how it was done:
function fireLoop()
{
window.requestAnimationFrame(fireLoop);
fire.update();
fire.render();
console.log('you spin me right round baby right round');
follow();
}
This is the loop I use. Every second Paul Irish's function will call the main loop. In this loop. I update the information choose the right animation that needs to be drawn and then I draw on the canvas (after having removed the previous element).
The follow function is the one that chooses the next coordinates for the animation. You'll have to change this part since, you don't want to move the canvas but move the animation. You can use the same code, but you need to apply location to where you want to draw on the canvas.
function follow()
{
$(fireCanvas).offset({
top: getTop(),
left: getLeft()
});
}
function getTop()
{
var off = $(fireCanvas).offset();
if(off.top != currentMousePos.y - $(fireCanvas).height() + 10)
{
if(off.top > currentMousePos.y - $(fireCanvas).height() + 10)
{
return off.top - 1;
}
else
{
return off.top + 1;
}
}
}
function getLeft()
{
var off = $(fireCanvas).offset();
if(off.left != currentMousePos.x - $(fireCanvas).width()/2)
{
if(off.left > currentMousePos.x - $(fireCanvas).width()/2)
{
return off.left - 1;
}
else
{
return off.left + 1;
}
}
}
var currentMousePos = { x: -1, y: -1 };
$(document).mousemove(function(event) {
currentMousePos.x = event.pageX;
currentMousePos.y = event.pageY;
});
If you want me to go into depth about anything specific let me know.

FlashCanvas drawImage NotWorking

I'm on Windows7 IE9 running in IE8. This works in IE9 only because I can use canvas however in IE8 it's suppose to fall back to flash canvas. Here is my source http://blog.jackadam.net/2010/alpha-jpegs/ NOW it seems im having a problem in IE with the context.drawImage not drawing the image? I've posted on the flashcanvas google group but they seem to take some time to repsond so was hoping there maybe a flashcanvas guru here.
;(function() {
var create_alpha_jpeg = function(img) {
var alpha_path = img.getAttribute('data-alpha-src')
if(!alpha_path) return
// Hide the original un-alpha'd
img.style.visiblity = 'hidden'
// Preload the un-alpha'd image
var image = document.createElement('img')
image.src = img.src + '?' + Math.random()
console.log(image.src);
image.onload = function () {
console.log('image.onload');
// Then preload alpha mask
var alpha = document.createElement('img')
alpha.src = alpha_path + '?' + Math.random()
alpha.onload = function () {
console.log('alpha.onload');
var canvas = document.createElement('canvas')
canvas.width = image.width
canvas.height = image.height
img.parentNode.replaceChild(canvas, img)
// For IE7/8
if(typeof FlashCanvas != 'undefined') FlashCanvas.initElement(canvas)
// Canvas compositing code
var context = canvas.getContext('2d')
context.clearRect(0, 0, image.width, image.height)
context.drawImage(image, 0, 0, image.width, image.height)
//context.globalCompositeOperation = 'xor'
//context.drawImage(alpha, 0, 0, image.width, image.height)
}
}
}
// Apply this technique to every image on the page once DOM is ready
// (I just placed it at the bottom of the page for brevity)
var imgs = document.getElementsByTagName('img')
for(var i = 0; i < imgs.length; i++)
create_alpha_jpeg(imgs[i])
})();
The solution to this was it only works with the older version of flashcanvas AND it only works with flashcanvas pro... as noted in the second footer of the website
This technique uses the globalCompositeOperation operation, which
requires FlashCanvas Pro. Free for non-profit use or just $31 for a
commercial license.
I got it working with flashcanvaspro. Depending which flash player it targets the max image size varies.
Flash Player 10 increased the maximum size of a bitmap to a maximum pixel count of 16,777,215.
Flash Player 9 limits (2880 x 2880 pixels).
https://helpx.adobe.com/flash-player/kb/size-limits-swf-bitmap-files.html
Need someone to update flashcanvas to the latest flash player

Rotating and Caching in canvas bug

I am making a game and in it I would like to have the ability to use cached canvas's instead of rotating the image every frame. I think I made a function for adding images that makes sense to me, but I am getting an error every frame that tells me that the canvas object is no longer available.
INVALID_STATE_ERR: DOM Exception 11: An attempt was made to use an
object that is not, or is no longer, usable.
You might also need to know that I am using object.set(); to go ahead and add that image to a renderArray. That may be affecting whether the canvas object is still avaliable?
Here is the function that returns a cached canvas, (I took it from a post on this website :D)
rotateAndCache = function(image, angle){
var offscreenCanvas = document.createElement('canvas');
var offscreenCtx = offscreenCanvas.getContext('2d');
var size = Math.max(image.width, image.height);
offscreenCanvas.width = size;
offscreenCanvas.height = size;
offscreenCtx.translate(size/2, size/2);
offscreenCtx.rotate(angle + Math.PI/2);
offscreenCtx.drawImage(image, -(image.width/2), -(image.height/2));
return offscreenCanvas;
}
And here is some more marked up code:
var game = {
render:function(){
//gets called every frame
context.clearRect(0, 0, canvas.width, canvas.height);
for(i = 0; i < game.renderArray.length; i++){
switch(game.renderArray[i].type){
case "image":
context.save();
context.translate(game.renderArray[i].x, game.renderArray[i].y);
context.rotate(Math.PI*game.renderArray[i].rotation/180);
context.translate(-game.renderArray[i].x, -game.renderArray[i].y);
context.drawImage(game.renderArray[i].image, game.renderArray[i].x, game.renderArray[i].y);
context.restore();
break;
}
if(game.renderArray[i].remove == true){
game.renderArray.splice(i,1);
if(i > 1){
i--;
}else{
break;
}
}
}
},
size:function(width, height){
canvas.height = height;
canvas.width = width;
return height + "," + width;
},
renderArray:new Array(),
//initialize the renderArray
image:function(src, angle){
if(angle != undefined){
//if the argument 'angle' was given
this.tmp = new Image();
this.tmp.src = src;
//sets 'this.image' (peach.image) to the canvas. It then should get rendered in the next frame, but apparently it doesn't work...
this.image = rotateAndCache(this.tmp, angle);
}else{
this.image = new Image();
this.image.src = src;
}
this.x = 0;
this.y = 0;
this.rotation = 0;
this.destroy = function(){
this.remove = true;
return "destroyed";
};
this.remove = false;
this.type = "image";
this.set = function(){
game.renderArray.push(this);
}
}
};
var canvas, context, peach;
$(document).ready(function(){
canvas = document.getElementById("canvas");
context = canvas.getContext("2d");
//make the variable peach a new game.image with src of meme.jpg and an angle of 20.
peach = new game.image('meme.jpg', 20);
peach.set();
game.size(700,500);
animLoop();
});
If you want, here is this project hosted on my site:
http://keirp.com/zap
There are no errors on your page, at least not anymore or not that I can see.
It's quite possible that the problem is an image that is not done loading. For instance that error will happen if you try to make a canvas pattern out of a not-yet-finished-loading image. Use something like pxloader or your own image loading function to make sure all the images are complete before you start drawing.
Anyway, it's nigh impossible to figure out what was or is happening since your code isn't actually giving any errors (anymore).

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