Is it possible to create an HTML canvas without a

问题:

I'd like to have an HTML canvas context that I can paint to and read off-screen (in this example, writing text and reading the shape that is created, but it's a general question). I may also want to use a canvas as an off-screen frame-buffer.

I suppose I could create a hidden DOM element but I'd rather create it from JavaScript (I may want to create and destroy a number of canvas at runtime).

Possible?

回答1:

You can create a new canvas element with document.createElement:

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

and then get the context from it. Just make sure you set the width and height. You don't have to add the canvas to the tree in order to make it work:

DEMO

But you definitely have to create that node. You could create a function for that though:

function createContext(width, height) {
    var canvas = document.createElement('canvas');
    canvas.width = width;
    canvas.height = height;
    return canvas.getContext("2d");
}

But that is where my competency ends... whether you can somehow transfer a context to another context or canvas, I don't know...

回答2:

Its old but what about saving one canvas with toDataURL and copying to the other with drawImage. you could also use save and restore to make a frame buffer

    function createCanvas(width, height) {
    var c = document.createElement('canvas');
    c.setAttribute('width', width);
    c.setAttribute('height', height);
    return c;
}

function canvasImg(canvas) {
    var ctx = canvas.getContext('2d');
    ctx.fillRect(0,0,canvas.width, canvas.height);
    var img = canvas.toDataURL('image/png');

    return img;
}

function placeImage(canvas, img) {
    var ctx = canvas.getContext('2d');
    ctx.drawImage(img, 0,0);
}

window.onload = function(){
    var canvas = createCanvas(400, 400);
    var hiddenCanvas = createCanvas(400,400);
    var i = canvasImg(hiddenCanvas);
    var img = new Image();
    img.src = i;
    placeImage(canvas, img);
    document.body.appendChild(canvas);
}