[whatwg] Canvas API: What should happen if non-finite floats are used

This seems like a strange choice of behavior. Given that this is very
likely a bug in the program, wouldn't it make more sense to throw an
exception as to make it easier to debug? Similar to for example
Node.appendChild when called with a null argument.

/ Jonas

On Tue, Sep 7, 2010 at 10:32 PM, Sam Weinig <weinig at apple.com> wrote:
> In 4.8.11.1 the spec does state:
>
> "Except where otherwise specified, for the 2D context interface, any method call with a numeric argument whose value is infinite or a NaN value must be ignored."
>
> -Sam
>
> On Sep 7, 2010, at 9:41 PM, Boris Zbarsky wrote:
>
>> Consider this testcase:
>>
>> <!doctype html>
>> <html>
>> ?<body>
>> ? ?<canvas id="c" width="200" height="200"></canvas>
>> ? ?<script>
>> ? ?try {
>> ? ? ?var c = document.getElementById("c"),
>> ? ? ?t = c.getContext("2d");
>> ? ? ?t.moveTo(100, 100);
>> ? ? ?t.lineTo(NaN, NaN);
>> ? ? ?t.lineTo(50, 25);
>> ? ? ?t.stroke();
>> ? ?} catch (e) {alert(e); }
>> ? ?</script>
>> ?</body>
>> </html>
>>
>> Behavior in the spec seems to be undefined (in particular, no mention is made as to what the canvas API functions are supposed to do if non-finite values are passed in). ?Behavior in browsers is:
>>
>> Presto: Throws NOT_SUPPORTED_ERR on that lineTo(NaN, NaN) call.
>> Gecko: Throws DOM_SYNTAX_ERR on that lineTo(NaN, NaN) call.
>> Webkit: Silently ignores the lineTo(NaN, NaN) call, and then
>> ? ? ? ?draws a line from (100,100) to (50, 25).
>>
>> Seems like the spec needs to define this.
>>
>> -Boris
>>
>> P.S. ?This isn't a hypothetical issue; this came up in a page that was trying to graph things using canvas and ending up with divide-by-0 all over the place. ?It "worked" in webkit (though not drawing the right thing, so much). ?It failed to draw anything in Presto or Gecko.
>
>

Received on Tuesday, 7 September 2010 22:36:31 UTC