[whatwg] Canvas Zero/NaN/Infinity issues
ian at hixie.ch
Tue May 15 18:36:38 PDT 2007
On Sat, 20 May 2006, Anne van Kesteren wrote:
> I think http://whatwg.org/specs/web-apps/current-work/#strokerect must
> have no effect when it has a zero height or width (or both). Currently
> Safari, Firefox and Opera act that way when they are both zero and
> Safari acts that way for all cases. Firefox and Opera draw a small line
> when either is larger than zero but that can easily be changed. It also
> makes the method more consistent with the other two.
> For those "If either height or width are zero, this method has no
> effect." should probably be changed to "If either height or width are
> zero, this method must have no effect."
Fixed, but not that way. Let me know if it's ok.
On Mon, 26 Mar 2007, Philip Taylor wrote:
> What should happen when Infinity or -Infinity or NaN are passed as float
> arguments? I assume there shouldn't be a type exception since they're
> perfectly valid floats (under the usual models of floating point
> arithmetic), though I don't know where/if that's defined. In some cases
> there is a logical behaviour (e.g. when translating a finite-sized
> object by infinity, or scaling an object like rect(-10,-10,20,20) by
> infinity then clipping it to the viewable area), but in most cases there
> isn't (e.g. rotating by infinity, or doing anything with NaN, when the
> output depends on those values).
> My experience with some 3d canvas code is that infinities come up in
> naturally harmless places, e.g. having a function that scales by x then
> translates by 1/x and wanting it to work when x=0 (which ought to draw
> nothing, since anything it draws is zero pixels wide), and it's a bit
> annoying to track down and fix those issues, so I'd probably like it if
> they were harmless in canvas methods. Opera appears to silently not draw
> anything if the transformation matrix is not finite, but Firefox throws
> exceptions when passing in non-finite arguments.
Specifically for transform(), setTransform(), scale(), and translate(),
I've made Infinity cause the canvas to stop drawing instead of raising an
exception. Everything else, exceptions.
On Wed, 4 Apr 2007, Philip Taylor wrote:
> What if offset is NaN? That is neither less than 0 nor greater than 1.
On Sat, 12 May 2007, Darin Adler wrote:
> > Changed to unsigned.
> If it's unsigned, it's ambiguous what behavior should be when an attempt
> INDEX_SIZE_ERR exception be raised? Should the value be ignored?
> I think I ran into this problem with HTMLOptionsCollection length
Fixed by adding a general rule to the conformance section.
On Sat, 5 May 2007, Darin Adler wrote:
> A while back I did some work on WebKit's canvas implementation and I
> noticed a few things in the canvas section of Web Apps that I'd like to
> see specified so they don't end up different between implementations:
> a) NAN arguments
> For the graphics context functions that take floating point values, I
> think the specification should say what the expected behavior is for:
> 1) NANs
> 2) non-floating point values
> 3) missing parameters
> b) excess arguments
1, 3, and b now raise exceptions except if otherwise specified. I haven't
yet defined 2. I'm not sure what it should say.
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