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[Diego Alberti]

Hi:

I'm trying to use paper.js to draw on top of an already drawn canvas.

my problem is (no matter what) when I add any shape the paper.js view is fulfilled on black occluding the previously drawn image.

It's quite impossible to paste real code so I'll try pseudo:

+ there's a canvas tag id "myCanvas"

+ paper.setup(canvas);

+ paper.view.autoUpdate = false;

+ another library renders a raster image on "myCanvas"

+ paper.js -> new paper.Path.circle(blabla);

+ paper.view.update()

the image does not appears. 

I'm pretty sure paper.js is filling with black because paper.view is smaller than the whole canvas. so I can actually see portions of the background image around.

I'm working with cornerstone.js a library for medical imaging.

make sense?

any though will be kindly appreciated.

thanks !

dx

 

[Sean Johnson]

I would suggest layering two canvases on top of each other using absolute positioning. The bottom canvas being your existing canvas, and the top being the paper.is one.

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[Michael Sartore]

Hi,

I had the same issue and solved it by adjusting the  "globalAlpha" property to 0.

See here...

[Diego Alberti]

thanks ! that's what actually did.

I'm gonna leave this here for further reference:

// https://developer.mozilla.org/en-US/docs/Web/API/Node/insertBefore

const canvas = evt.detail.element.querySelector('canvas.cornerstone-canvas');

var otherCanvas = document.createElement('canvas');

otherCanvas.setAttribute('style', 'position: absolute');

canvas.parentNode.insertBefore(otherCanvas, canvas);

paper.setup(otherCanvas);

paper.view.autoUpdate = false;

dx

[Diego Alberti]

thank you. solved already. ! I'll try it later anyway.

thx

dx