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canvas like framebuffer work on chrome but not in firefox

I try to use a canvas like framebuffer, in chrome work ok but in firefox not.
Any expert in firefox can see the code?
in
https://github.com/r3www/r3/blob/master/compiler.js
lines 445..
function r3init() {
canvas = document.getElementById('canvas');
ctx = canvas.getContext('2d',{alpha:false,preserveDrawingBuffer:true});
imageData=ctx.getImageData(0,0,canvas.width, canvas.height);
buf8=new Uint8ClampedArray(memdata,0,imageData.data.length);
meminidata=imageData.data.length;// dinamic???
}
function redraw() {
imageData.data.set(buf8);ctx.putImageData(imageData,0,0);
}
r3init set the canvas and redraw copy the memory of framebuffer to canvas.
for try go to
https://rawgit.com/r3www/r3/master/index.html
and click run.
Thank's

Your problem is that you are relying on a Chrome bug, which doesn't respect your alpha: false CanvasRenderingContext2DSetting, when you put a transparent ImageData.
When you do ctx.putImageData(ImageData, x, y) to such a context, the alpha channel should be ignored by the algorithm, and always fully opaque => 255.
From specs' note:
Thus, the bitmap of such a context starts off as opaque black instead of transparent black; clearRect() always results in opaque black pixels, every fourth byte from getImageData() is always 255, the putImageData() method effectively ignores every fourth byte in its input, and so on.
So, I didn't dig exactly what you do to this data, but it seems that you assume the alpha channel is initially 0, while it actually shouldn't be.
A simple fix, is to initialize your context with the default alpha set.
Also note that preserveDrawingBuffer is a webgl setting, there is no drawing buffer in 2D context.
// alpha for everyone
ctx = canvas.getContext('2d');
Simple test for currently broken Chrome (at least v69.0.3497)
const alpha = document.createElement('canvas')
.getContext('2d');
const opaque = document.createElement('canvas')
.getContext('2d', {
alpha: false
});
// a transparent ImageData
const transp = alpha.createImageData(300, 150);
// alpha channel should be ignored
opaque.putImageData(transp,0,0);
const opaque_c = opaque
.getImageData(0,0,4,4)
.data[3];
const alpha_c = alpha
.getImageData(0,0,4,4)
.data[3]
console.log('opaque', opaque_c); // should be 255
console.log('alpha', alpha_c); // should be 0

Canvas linear downscaling

im trying to do a downscale of an image using canvas to later use the data for a hash compare. however i noticed that the canvas (or at least the simple code i use) uses no mipmap filter resulting in very sharp result and makes the test against another existing hash fail (downscaling the image in gimp using linear works as expected). the code i use to downscale is
var canvas = document.createElement("canvas");
canvas.width = width; canvas.height = height;
var context = canvas.getContext('2d');
context.drawImage(image, 0, 0, width, height);
return context.getImageData(0, 0, width, height).data;
this results in this image (left) to the expected (right)
how can i get the canvas to downscale linear?

The new canvas draft specify a way to set re-sampling/interpolation for the canvas. The current method is always bi-linear, or nearest-neighbor if imageSmoothingEnabled = false (both methods are for both up-scaling and down-sampling). The new property is called imageSmoothingQuality:
context . imageSmoothingQuality [ = value ]
The value can be "low", "medium" and "high" (for example something like bi-cubic/Lanczos). However, no browsers has yet implemented this at the moment of writing this and the actual algorithms used for each value is not mandated.
The alternative approaches is to manually re-sample when you need changes above 50% using multiple steps, or to implement a re-sampling algorithm.
Here is an example of multiple steps to achieve bi-cubic quality level (and avoids initial CORS problems), as well as one showing the Lanczos algorithm (need CORS requirements to be met).
In addition to that you can apply sharpening convolution to compensate for some of the lost sharpness.

Resizing images using createjs / easeljs

I'd like to dynamically downsize some images on my canvas using createjs, and then store the smaller images to be displayed when zooming out of the canvas for performance reasons. Right now, I'm using the following code:
var bitmap = createjs.Bitmap('somefile.png');
// wait for bitmap to load (using preload.js etc.)
var oc = document.createElement('canvas');
var octx = oc.getContext('2d');
oc.width = bitmap.image.width*0.5;
oc.height = bitmap.image.height*0.5;
octx.drawImage(bitmap.image, 0, 0, oc.width, oc.height);
var dataUrl = oc.toDataURL('image/png'); // very expensive
var smallBitmap = new createjs.Bitmap(dataUrl);
This works, but:
The toDataURL operation is very expensive when converting to image/png and too slow to use in practice (and I can't convert to the faster image/jpeg due to the insufficient quality of the output for all settings I tried)
Surely there must be a way to downsize the image without having to resort to separate canvas code, and then do a conversion manually to draw onto the createjs Bitmap object??
I've also tried:
octx.drawImage(bitmap.image, 0, 0, oc.width, oc.height);
var smallBitmap = new createjs.Bitmap(oc);
But although very fast, this doesn't seem to actually work (and in any case I'm having to create a separate canvas element every time to facilitate this.)
I'm wondering if there is a way that I can use drawImage to draw a downsampled version of the bitmap into a createjs Bitmap instance directly without having to go via a separate canvas object or do a conversion to string?
If I understand correctly, internally this is how the createjs cache property works (i.e. uses drawImage internally to write into the DisplayObject) but I'm unable to figure out how use it myself.

You have tagged this post with createjs and easeljs, but your examples show plain Canvas context usage for scaling.
You can use the scale parameter on Bitmap.cache() to get the result you want, then reuse the cacheCanvas as necessary.
// This will create a half-size cache (50%)
// But scale it back up for you when it displays on the stage
var bmp = new createjs.Bitmap(img);
bmp.cache(0, 0, img.width, img.height, 0.5);
// Pull out the generated cache and use it in a new Bitmap
// This will display at the new scaled size.
var bmp2 = new createjs.Bitmap(bmp.cacheCanvas);
// Un-cache the first one to reset it if you want
bmp.uncache();
Here is a fiddle to see it in action: http://jsfiddle.net/lannymcnie/ofdsyn7g/
Note that caching just uses another canvas with a drawImage to scale it down. I definitely would stay away from toDataURL, as it not performant at all.

Hand-create images in javascript and draw with respect to the alpha channel?

I'm currently trying to create a page with dynamically generated images, which are not shapes, drawn into a canvas to create an animation.
The first thing I tried was the following:
//create plenty of those:
var imageArray = ctx.createImageData(0,0,16,8);
//fill them with RGBA values...
//then draw them
ctx.putImageData(imageArray,x,y);
The problem is that the images are overlapping and that putImageData simply... puts the data in the context, with no respect to the alpha channel as specified in the w3c:
pixels in the canvas are replaced wholesale, with no composition, alpha blending, no shadows, etc.
So I thought, well how can I use Images and not ImageDatas?
I tried to find a way to actually put the ImageData object back into an image but it appears it can only be put in a canvas context. So, as a last resort, I tried to use the toDataURL() method of a 16x8 canvas(the size of my images) and to stick the result as src of my ~600 images.
The result was beautiful, but was eating up 100% of my CPU...(which it did not with putImageData, ~5% cpu) My guess is that for some unknown reason the image is re-loaded from the image/png data URI each time it is drawn... but that would be plain weird... no? It also seems to take a lot more RAM than my previous technique.
So, as a result, I have no idea how to achieve my goal.
How can I dynamically create alpha-channelled images in javascript and then draw them at an appreciable speed on a canvas?
Is the only real alternative using a Java applet?
Thanks for your time.

Not knowing, what you really want to accomplish:
Did you have a look at the drawImage-method of the rendering-context?
Basically, it does the composition (as specified by the globalCompositeOperation-property) for you -- and it allows you to pass in a canvas element as the source.
So could probably do something along the lines of:
var offScreenContext = document.getCSSCanvasContext( "2d", "synthImage", width, height);
var pixelBuffer = offScreenContext.createImageData( tileWidth, tileHeight );
// do your image synthesis and put the updated buffer back into the context:
offScreenContext.putImageData( pixelBuffer, 0, 0, tileOriginX, tileOriginY, tileWidth, tileHeight );
// assuming 'ctx' is the context of the canvas that actually gets drawn on screen
ctx.drawImage(
offScreenContext.canvas, // => the synthesized image
tileOriginX, tileOriginY, tileWidth, tileHeight, // => frame of offScreenContext that get's drawn
originX, originY, tileWidth, tileHeight // => frame of ctx to draw in
);
Assuming that you have an animation you want to loop over, this has the added benefit of only having to generate the frames once into some kind of sprite-map so that in subsequent iterations you'll only ever need to call ctx.drawImage() -- at the expense of an increased memory footprint of course...

Why don't you use SVG?
If you have to use canvas, maybe you could implement drawing an image on a canvas yourself?
var red = oldred*(1-alpha)+imagered*alpha
...and so on...

getCSSCanvasContext seems to be WebKit only, but you could also create an offscreen canvas like this:
var canvas = document.createElement('canvas')
canvas.setAttribute('width',300);//use whatever you like for width and height
canvas.setAttribute('height',200);
Which you can then draw to and draw onto another canvas with the drawImage method.

Get image line co-ordinates for canvas

I just started to work with canvas.
I need to simulate some image in pure canvas.
image => tool => [1, 20, 80, 45.....] => canvas => canvas render image
some picuture coordinates this picture but rendered(created) via canvas
Are there any tools that help to get image lines coordinates (to map)?
So, next, I could just use them, and get a pure canvas image.

If I understood your comment correctly, you either want to draw an image onto a canvas, or convert it to vector data and then draw that on the canvas.
Drawing an image on a canvas
This is by far the simplest solution. Converting raster images to vector data is a complicated process involving advanced algorithms, and still it's not perfect.
Rendering an image on a canvas is actually very simple:
// Get the canvas element on the page (<canvas id="canvas"> in the HTML)
var ctx = document.getElementById('canvas').getContext('2d');
// Create a new image object which will hold the image data that you want to
// render.
var img = new Image();
// Use the onload event to make the code in the function execute when the image
// has finished loading.
img.onload = function () {
// You can use all standard canvas operations, of course. In this case, the
// rotate function to rotate the image 45 degrees.
ctx.rotate(Math.PI / 4);
// Draw image at (0, 0)
ctx.drawImage(img, 0, 0);
}
// Tell the image object to load an image.
img.src = 'my_image.png';
Converting a raster image to vector data
This is a complicated process, so I won't give you the whole walkthrough. First of all, you can give up on trying to implement this yourself right now, because it requires a lot of work. However, there are applications and services that do this for you:
http://vectormagic.com/home
Works great, but you will have to pay for most of the functionality
How to convert SVG files to other image formats
A good list of applications that can do this for you
After this, you can store the vector data as SVG and use the SVG rendering that some browsers have, or a library such as SVGCanvas to render SVG onto a canvas. You can probably use that library to convert the resulting image to a list of context operations instead of converting from SVG every time.