How to use x2 canvas elements and rendering paper.js on img capture of html5 video to base64 - html5-canvas

Question

Still very much a newbie to coding, so please be gentle :)
I'm hoping someone might be able to help how to use Paper.js on a second canvas after the first one has been executed?
I'm trying to use x2 canvas elements:
Canvas 1 - to capture a html5 video image still and convert to base64 (tick :-) = done)
Canvas 2 - Use the base64 image and perform the 'Working with Rasters to find the colors of pixels' and convert to circle paths (boo = fail :-( )
Something like this:
The code:
<script src="https://cdn.jsdelivr.net/npm/hls.js#latest"></script>
<video id="video" preload="auto" muted="" playsinline="" width="580" src="blob:https://www.georgefisher.co.uk/78e3a45c-ae07-4ea5-af56-45a5ed9cf1b0"></video>
<script>
var video = document.getElementById('video');
var videoSrc = 'https://camsecure.co/HLS/georgefisher.m3u8';
if (Hls.isSupported()) {
var hls = new Hls();
hls.loadSource(videoSrc);
hls.attachMedia(video);
}
else if (video.canPlayType('application/vnd.apple.mpegurl')) {
video.src = videoSrc;
}
video.play()
</script>
<br>
<button onclick="capture()">Capture</button>
<br>
<canvas id="canvas" style="overflow:auto">
</canvas>
<canvas id="canvas2" resize>
<img src="" id="myImg"/></canvas>
var resultb64="";
function capture() {
var canvas = document.getElementById('canvas');
var video = document.getElementById('video');
canvas.width = video.videoWidth/4;
canvas.height = video.videoHeight/4;
canvas.getContext('2d').drawImage(video, 0, 0, video.videoWidth/4, video.videoHeight/4);
resultb64=canvas.toDataURL();
document.querySelector("#myImg").src = canvas.toDataURL();
}
/*Paper JS Setup for working in CodePen */
/* ====================== *
* 0. Initiate Canvas *
* ====================== */
// expose paperjs classes into global scope
paper.install(window);
// Only executed our code once the DOM is ready.
window.onload = function() {
// bind paper to the canvas
paper.setup('canvas2');
// paper.activate();
// Get a reference to the canvas object
var canvas = document.getElementById('canvas2');
var ctx = canvas.getContext('2d');
// console.log(ctx, image);
// ctx.drawImage(image, 0, 0);
// return;
// }
// Create a raster item using the image id='' tag
var image = document.querySelector('img');
var raster = new Raster(image);
// Hide the raster:
raster.visible = false;
// The size of our grid cells:
var gridSize = 15;
// Space the cells by 120%:
var spacing = 1
;
// As the web is asynchronous, we need to wait for the raster to load before we can perform any operation on its pixels.
raster.onLoad = function() {
// Since the example image we're using is much too large, and therefore has way too many pixels, lets downsize it to 40 pixels wide and 30 pixels high:
raster.size = new Size(40, 30);
for (var y = 0; y < raster.height; y++) {
for(var x = 0; x < raster.width; x++) {
// Get the color of the pixel:
var color = raster.getPixel(x, y);
// Create a circle shaped path:
var path = new Path.Circle({
center: new Point(x, y).multiply(gridSize),
radius: gridSize / 2 / spacing,
});
// Set the fill color of the path to the color
// of the pixel:
path.fillColor = color;
}
}
// Move the active layer to the center of the view, so all the created paths in it appear centered.
project.activeLayer.position = view.center;
}
}
I've tried giving the second canvas a different Id="canvas2" and referencing that, which I can see in the console. However, nothing appears in the second canvas and the paper.js script doesn't seem to execute, can someone help me understand why?
Please see also see link to the fiddle below:
https://jsfiddle.net/jmnes/o4Lpkfs6/1/

Answer 1

Alternatives method.
You don't need to capture the video, you don't need to capture the pixels using paper.js and raster. You don't need to find the color of each circle and draw it.
All these methods are slow, complex, and power hungry.
You can create a mask and mask out the circles, with the colors drawn from a smaller canvas with a res that matches the number off circles.
How to
Add one (main canvas) canvas to the DOM. This will display the result
Create 2 offscreen canvas.
One (color canvas) has the same resolution as the circles you want to display. Eg if you have 30 by 40 circle the canvas res should be 30 by 40
One (mask canvas) is the circle mask. It is the same resolution as the main canvas. Draw the circles all in one color on this canvas.
Then rendering once a frame
Draw the video on the color canvas to fit.
Turn off smoothing on the main canvas eg ctxMain.imageSmoothingEnabled = false
Draw the color canvas onto the main canvas to fit.
This will draw a color square at each circle position. ctx.drawImage(colorCanvas, 0, 0, mainCanvas.width, mainCanvas.height)
Set composite operation "destination-in" eg ctxMain.globalCompositeOperation = "destination-in"
Draw the mask canvas (canvas with circles on it) onto the main canvas. This will remove pixels outside each circle.
Restore default composite operation for the main canvas ctxMain.globalCompositeOperation = "source-over"
All done for a real-time FX on almost any device.
The above methods is the fastest way to render the effect you are after using the 2D API