Stream canvas to imgITools to make ico

Question

So on WinXP I have been having a hard time converting a PNG file to an ICO with canvas. I found this method encodeImage. I don't know if it works but it looks promising but I can't figure out how to feed the image I drew on a canvas into imgITools.decodeData.

What should I use for aImageStream and/or aMimeType?

imgTools.decodeImageData(aImageStream, aMimeType, imgContainer);

This is more of my code:

 img['asdf'].file = new FileUtils.File(myPathHere);

let iconStream;
try {
  let imgTools = Cc["@mozilla.org/image/tools;1"]
                    .createInstance(Ci.imgITools);
  let imgContainer = { value: null };

  imgTools.decodeImageData(aImageStream, aMimeType, imgContainer);
  iconStream = imgTools.encodeImage(imgContainer.value,
                                    "image/vnd.microsoft.icon",
                                    "format=bmp;bpp=32");
} catch (e) {
  alert('failure converting icon ' + e)
  throw("processIcon - Failure converting icon (" + e + ")");
}

let outputStream = FileUtils.openSafeFileOutputStream(img['asdf'].file);
NetUtil.asyncCopy(iconStream, outStream, netutilCallback);

Answer 1

Since you're having a canvas already(?), it would be probably easier to use either on of the following canvas methods:

• toDataURI/toDataURIHD
• toBlob/toBlobHD
• mozFetchAsStream

There is also the undocumented -moz-parse-options:, e.g -moz-parse-options:format=bmp;bpp=32. (ref-tests seem to depend on it, so it isn't going away anytime soon I'd think).

So, here is an example for loading stuff into an ArrayBuffer.

(canvas.toBlobHD || canvas.toBlob).call(canvas, function (b) {
    var r = new FileReader();
    r.onloadend = function () {
        // r.result contains the ArrayBuffer.
    };
    r.readAsArrayBuffer(b);
}, "image/vnd.microsoft.icon", "-moz-parse-options:format=bmp;bpp=32");

Here is a more complete example fiddle creating a 256x256 BMP icon.

Since you likely want to feed that data into js-ctypes, having an ArrayBuffer is great because you can create pointers from it directly, or write it to a file using OS.File.