[whatwg] Canvas patterns, and miscellaneous other things

Philip Taylor excors+whatwg at gmail.com
Sat Feb 2 12:10:30 PST 2008

On 31/01/2008, Ian Hickson <ian at hixie.ch> wrote:
> I've made toDataURL() return "data:," if it's faced with a 0-pixel image.
> It's arbitrary, but I guess it represents the image, at least!

That makes the "Note: When trying to use types other than image/png,
authors can check if the image was really returned in the requested
format by checking to see if the returned string starts with one the
exact strings "data:image/png," or "data:image/png;"." now incorrect.
The non-image/png format might be unsupported, but someone might be
drawing a 0-pixel image and they'll get back something that doesn't
start with data:image/png[,;].

It does seem pretty weird to return text/plain content when asked for
an image. But I guess it's safer than e.g. returning an empty string,
since it won't get misinterpreted as a relative address when people do
img.src=canvas.toDataURL(), and I can't think of a better idea.

> User agents may impose implementation-specific limits on otherwise
> unconstrained inputs, e.g. to prevent denial of service attacks, to guard
> against running out of memory, or to work around platform-specific
> limitations. (See ...#hardwareLimitations.)

Does anything say that those limitations should be imposed by throwing
an exception, and not by e.g. returning null or aborting the entire

> I'm assuming that the DOM Bindings
> for JS spec will define how 'undefined' really means 'null'

Hmm, I can imagine 'undefined' converted to a DOMString becoming the
string "undefined". (That's at least what
document.createTextNode(undefined) does). But I can just assume for
now it's meant to work like null.

Philip Taylor
excors at gmail.com

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