I'm working with a canvas element with a height of 开发者_Go百科600 to 1000 pixels and a width of several tens or hundreds of thousands of pixels. However, after a certain number of pixels (obviously unknown), the canvas no longer display shapes I draw with JS.

Does anyone know if there's a limit?

Tested both in Chrome 12 and Firefox 4.

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Updated 10/13/2014

All tested browsers have limits to the height/width of canvas elements, but many browsers also limit the total area of the canvas element. The limits are as follows for the browsers I'm able to test:

Chrome:

Maximum height/width: 32,767 pixels
Maximum area: 268,435,456 pixels (e.g., 16,384 x 16,384)

Firefox:

Maximum height/width: 32,767 pixels
Maximum area: 472,907,776 pixels (e.g., 22,528 x 20,992)

IE:

Maximum height/width: 8,192 pixels
Maximum area: N/A

IE Mobile:

Maximum height/width: 4,096 pixels
Maximum area: N/A

Other:

I'm not able to test other browsers at this time. Refer to the other answers on this page for additional limits.

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Exceeding the maximum length/width/area on most browsers renders the canvas unusable. (It will ignore any draw commands, even in the usable area.) IE and IE Mobile will honor all draw commands within the usable space.

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The accepted answer is outdated and incomplete.

Browsers impose different canvas size limitations, but these limitations often change based on the platform and hardware available. This makes it difficult to make statements like "the maximum canvas [area/height/width] of [browser] is [value]" because [value] can change based the operating system, available RAM, or GPU type.

There are two approaches to working with large HTML <canvas> elements:

1. Limit canvas dimensions to those known to work on all supported platforms.
2. Programmatically determine canvas limitations on the client before rendering.

Those looking to programmatically determine canvas limitations on the client should consider using canvas-size.

• GitHub: https://github.com/jhildenbiddle/canvas-size
• NPM: https://www.npmjs.com/package/canvas-size

From the docs:

The HTML canvas element is widely supported by modern and legacy browsers, but each browser and platform combination imposes unique size limitations that will render a canvas unusable when exceeded. Unfortunately, browsers do not provide a way to determine what their limitations are, nor do they provide any kind of feedback after an unusable canvas has been created. This makes working with large canvas elements a challenge, especially for applications that support a variety of browsers and platforms.

This micro-library provides the maximum area, height, and width of an HTML canvas element supported by the browser as well as the ability to test custom canvas dimensions. By collecting this information before a new canvas element is created, applications are able to reliably set canvas dimensions within the size limitations of each browser/platform.

Test results for a variety of platform and browser combinations are available here:

• Test Results: https://github.com/jhildenbiddle/canvas-size#test-results

Full disclosure, I am the author of the library. I created it back in 2014 and recently revisited the code for a new canvas-related project. I was surprised to find the same lack of available tools for detecting canvas size limitations in 2018 so I updated code, released it, and hope it helps others running into similar issues.

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I've ran into out of memory errors on Firefox with canvas heights greater than 8000, chrome seems to handle much higher, at least to 32000.

EDIT: After running some more tests, I've found some very strange errors with Firefox 16.0.2.

First, I seem to get different behavior from in memory (created in javascript) canvas as opposed to html declared canvas.

Second, if you don't have the proper html tag and meta charset, the canvas might be restricted to 8196, otherwise you can go up to 32767.

Third, if you get the 2d context of the canvas and then change the canvas size, you might be restricted to 8196 as well. Simply setting the canvas size before grabbing the 2d context allows you to have up to 32767 without getting memory errors.

I haven't been able to consistently get the memory errors, sometimes it's only on the first page load, and then subsequent height changes work. This is the html file I was testing with http://pastebin.com/zK8nZxdE.

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iOS max canvas size (width x height):

 iPod Touch 16GB = 1448x1448
 iPad Mini       = 2290x2289
 iPhone 3        = 1448x1448
 iPhone 5        = 2290x2289

tested on march 2014.

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To expand a bit on @FredericCharette answer: As per safari's content guide under section "Know iOS Resource Limits":

The maximum size for a canvas element is 3 megapixels for devices with less than 256 MB RAM and 5 megapixels for devices with greater or equal than 256 MB RAM

Therefore, any size variation of 5242880 (5 x 1024 x 1024) pixels will work on large memory devices, otherwise it's 3145728 pixels.

Example for 5 megapixel canvas (width x height):

Any total <= 5242880
--------------------
5 x 1048576 ~= 5MP   (1048576 = 1024 x 1024)
50 x 104857 ~= 5MP
500 x 10485 ~= 5MP

and so on..

The largest SQUARE canvases are ("MiB" = 1024x1024 Bytes):

device < 256 MiB   device >= 256 MiB   iPhone 6 [not confirmed]
-----------------  -----------------   ---------------------
<= 3145728 pixels  <= 5242880 pixels   <= 16 x 1024 x 1024 p
1773 x 1773        2289 x 2289         4096 x 4096

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According to w3 specs, the width/height interface is an unsigned long - so 0 to 4,294,967,295 (if I remember that number right -- might be off a few).

EDIT: Strangely, it says unsigned long, but it testing shows just a normal long value as the max: 2147483647. Jsfiddle - 47 works but up to 48 and it reverts back to default.

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Even though the canvas will allow you to put height=2147483647, when you start drawing, nothing will happen

Drawing happens only when I bring the height back to 32767

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iOS has different limits.

Using the iOS 7 simulator I was able to demonstrate the limit is 5MB like this:

var canvas = document.createElement('canvas');
canvas.width = 1024 * 5;
canvas.height = 1024;
alert(canvas.toDataURL('image/jpeg').length);
// prints "110087" - the expected length of the dataURL

but if I nudge the canvas size up by a single row of pixels:

var canvas = document.createElement('canvas');
canvas.width = 1024 * 5;
canvas.height = 1025;
alert(canvas.toDataURL('image/jpeg'));
// prints "data:," - a broken dataURL

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On PC-
I don't think there is a restriction but yes you can get out of memory exception.

On Mobile devices-
Here is the restrictions for the canvas for mobile devices:-

The maximum size for a canvas element is 3 megapixels for devices with less than 256 MB RAM and 5 megapixels for devices with greater or equal than 256 MB RAM.

So for example - if you want to support Apple’s older hardware, the size of your canvas cannot exceed 2048×1464.

Hope these resources will help you to pull you out.

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When you are using WebGL canvases, the browsers (including the desktop ones) will impose extra limits on the size of the underlying buffer. Even if your canvas is big, e.g. 16,000x16,000, most browsers will render a smaller (let's say 4096x4096) picture, and scale it up. That might cause ugly pixelating, etc.

I have written some code to determine that maximum size using exponential search, if anyone ever needs it. determineMaxCanvasSize() is the function you are interested in.

function makeGLCanvas()
{
    // Get A WebGL context
    var canvas = document.createElement('canvas');
    var contextNames = ["webgl", "experimental-webgl"];
    var gl = null;
    for (var i = 0; i < contextNames.length; ++i)
    {
        try
        {
            gl = canvas.getContext(contextNames[i], {
                // Used so that the buffer contains valid information, and bytes can
                // be retrieved from it. Otherwise, WebGL will switch to the back buffer
                preserveDrawingBuffer: true
            });
        }
        catch(e) {}
        if (gl != null)
        {
            break;
        }
    }
    if (gl == null)
    {
        alert("WebGL not supported.\nGlobus won't work\nTry using browsers such as Mozilla " +
            "Firefox, Google Chrome or Opera");
        // TODO: Expecting that the canvas will be collected. If that is not the case, it will
        // need to be destroyed somehow.
        return;
    }

    return [canvas, gl];
}

// From Wikipedia
function gcd(a,b) {
    a = Math.abs(a);
    b = Math.abs(b);
    if (b > a) {var temp = a; a = b; b = temp;}
    while (true) {
        if (b == 0) return a;
        a %= b;
        if (a == 0) return b;
        b %= a;
    }
}

function isGlContextFillingTheCanvas(gl) {
    return gl.canvas.width == gl.drawingBufferWidth && gl.canvas.height == gl.drawingBufferHeight;
}

// (See issue #2) All browsers reduce the size of the WebGL draw buffer for large canvases 
// (usually over 4096px in width or height). This function uses a varian of binary search to
// find the maximum size for a canvas given the provided x to y size ratio.
//
// To produce exact results, this function expects an integer ratio. The ratio will be equal to:
// xRatio/yRatio.
function determineMaxCanvasSize(xRatio, yRatio) {
    // This function works experimentally, by creating an actual canvas and finding the maximum
    // value, the browser allows.
    [canvas, gl] = makeGLCanvas();

    // Reduce the ratio to minimum
    gcdOfRatios = gcd(xRatio, yRatio);
    [xRatio, yRatio] = [xRatio/gcdOfRatios, yRatio/gcdOfRatios];

    // if the browser cannot handle the minimum ratio, there is not much we can do
    canvas.width = xRatio;
    canvas.height = yRatio;

    if (!isGlContextFillingTheCanvas(gl)) {
        throw "The browser is unable to use WebGL canvases with the specified ratio: " + 
            xRatio + ":" + yRatio;
    }

    // First find an upper bound
    var ratioMultiple = 1;  // to maintain the exact ratio, we will keep the multiplyer that
                            // resulted in the upper bound for the canvas size
    while (isGlContextFillingTheCanvas(gl)) {
        canvas.width *= 2;
        canvas.height *= 2;
        ratioMultiple *= 2;
    }

    // Search with minVal inclusive, maxVal exclusive
    function binarySearch(minVal, maxVal) {
        if (minVal == maxVal) {
            return minVal;
        }

        middle = Math.floor((maxVal - minVal)/2) + minVal;

        canvas.width = middle * xRatio;
        canvas.height = middle * yRatio;

        if (isGlContextFillingTheCanvas(gl)) {
            return binarySearch(middle + 1, maxVal);
        } else {
            return binarySearch(minVal, middle);
        }
    }

    ratioMultiple = binarySearch(1, ratioMultiple);
    return [xRatio * ratioMultiple, yRatio * ratioMultiple];
}

Also in a jsfiddle https://jsfiddle.net/1sh47wfk/1/

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The limitations for Safari (all platforms) are much lower.

Known iOS/Safari Limitations

For example, I had a 6400x6400px canvas buffer with data drawn onto it. By tracing/ exporting the content and by testing on other browsers, I was able to see that everything was fine. But on Safari, it would skip the drawing of this specific buffer onto my main context.

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I tried to programmatically figure out the limit: setting canvas size starting from 35000, stepping down by 100 until valid size is found. In every step writing the right-bottom pixel and then reading it. It works - with caution.

The speed is acceptable if either width or height is set to some low value (eg. 10-200) this way: get_max_canvas_size('height', 20).

But if called without width or height like get_max_canvas_size(), the created canvas is so big that reading SINGLE pixel color is very slow, and in IE causes serious hang.

If this like test could be done someway without reading pixel value, the speed would be acceptable.

Of course the easiest way to detect maximum size would be some native way to query the max width and height. But Canvas is 'a living standard', so may be it is coming some day.

http://jsfiddle.net/timo2012/tcg6363r/2/ (Be aware! Your browser may hang!)

if (!Date.now)
{
  Date.now = function now()
  {
    return new Date().getTime();
  };
}

var t0 = Date.now();
//var size = get_max_canvas_size('width', 200);
var size = get_max_canvas_size('height', 20);
//var size = get_max_canvas_size();
var t1 = Date.now();
var c = size.canvas;
delete size.canvas;
$('body').append('time: ' + (t1 - t0) + '<br>max size:' + JSON.stringify(size) + '<br>');
//$('body').append(c);

function get_max_canvas_size(h_or_w, _size)
{
  var c = document.createElement('canvas');
  if (h_or_w == 'height') h = _size;
  else if (h_or_w == 'width') w = _size;
  else if (h_or_w && h_or_w !== 'width' && h_or_w !== 'height' || !window.CanvasRenderingContext2D)
    return {
      width: null,
      height: null
    };
  var w, h;
  var size = 35000;
  var cnt = 0;
  if (h_or_w == 'height') w = size;
  else if (h_or_w == 'width') h = size;
  else
  {
    w = size;
    h = size;
  }

  if (!valid(w, h))
    for (; size > 10; size -= 100)
    {
      cnt++;
      if (h_or_w == 'height') w = size;
      else if (h_or_w == 'width') h = size;
      else
      {
        w = size;
        h = size;
      }
      if (valid(w, h)) break;
    }
  return {
    width: w,
    height: h,
    iterations: cnt,
    canvas: c
  };

  function valid(w, h)
  {
    var t0 = Date.now();
    var color, p, ctx;
    c.width = w;
    c.height = h;
    if (c && c.getContext)
      ctx = c.getContext("2d");
    if (ctx)
    {
      ctx.fillStyle = "#ff0000";
      try
      {
        ctx.fillRect(w - 1, h - 1, 1, 1);
        p = ctx.getImageData(w - 1, h - 1, 1, 1).data;
      }
      catch (err)
      {
        console.log('err');
      }

      if (p)
        color = p[0] + '' + p[1] + '' + p[2];
    }
    var t1 = Date.now();

    if (color == '25500')
    {
      console.log(w, h, true, t1 - t0);
      return true;
    }
    console.log(w, h, false, t1 - t0);
    return false;
  }
}

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You could chunk it and in javascript auto add as many smaller canvases as needed and draw the elements on the appropriate canvas. You may still run out of memory eventually but would get you by the single canvas limit.

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I don't know how to detect the max possible size without itteration, but you can detect if a given canvas size works by filling a pixel and then reading the colour back out. If the canvas has not rendered then the color you get back will not match. W

partial code:

function rgbToHex(r, g, b) {
    if (r > 255 || g > 255 || b > 255)
        throw "Invalid color component";
    return ((r << 16) | (g << 8) | b).toString(16);
}
var test_colour = '8ed6ff';
working_context.fillStyle = '#' + test_colour;
working_context.fillRect(0,0,1,1);
var colour_data = working_context.getImageData(0, 0, 1, 1).data;
var colour_hex = ("000000" + rgbToHex(colour_data[0], colour_data[1], colour_data[2])).slice(-6);