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Re: [css3-values] Allow multiple values to be specified for max-width

From: Aryeh Gregor <Simetrical+w3c@gmail.com>
Date: Wed, 22 Jul 2009 01:01:06 +0000
Message-ID: <7c2a12e20907211801x4041737bw9188277a0bdd93a6@mail.gmail.com>
To: "Belov, Charles" <Charles.Belov@sfmta.com>
Cc: www-style@w3.org, Fran├žois REMY <fremycompany_pub@yahoo.fr>
On Tue, Jul 21, 2009 at 11:55 PM, Belov, Charles<Charles.Belov@sfmta.com> wrote:
> I see that the minimum operator for the calc function is not currently part of the working draft and is considered as a future operator for calc.
>
> I believe the need for choosing between the minimum of two max-widths would be a justification for including the minimum operator in the working draft.

Are browsers support to support mod for floating-point numbers?
Because if val - val mod 1 is equivalent to, for instance, floor(val)
(as in Python), then you could do something like

min(x, y) = 0.5*(x + y - abs(x - y))
abs(x) = sgn(x)*x
sgn(x) = 2*(x/1000000 - (x/1000000) mod 1) + 1 (if x is reasonably small)

Thus

>>> def f(x, y):
...     return 0.5*(x + y - (2*((x - y)/1000000 - ((x - y)/1000000) %
1) + 1)*(x - y))
...
>>> f(7, 14.2)
7.0
>>> f(7, 6.4)
6.4000000000000004
>>> f(-31, 927)
-31.0
>>> f(-8, -19)
-19.0

Also, you know you can do trig functions, exponentials, and logarithms
using Taylor series, right?  Actually, you can do any function
differentiable on the complex plane in a disk containing the range of
values you have to deal with!  Who said a good grounding in analysis
isn't useful in real life?  :D



. . . okay, now, seriously.  A few issues here:

1) The mod operator has to be defined better.  What does it do with
floating-point numbers, and what does it do with negative numbers?
I'd say it should definitely be defined to handle floating-points as
expected.  For negative numbers, I don't know, they don't come up too
often in CSS.  The spec should clarify this in any event.

2) A min() function would definitely be very useful.  There would
surely be no problem in implementing it, right?

3) I can *guarantee* that some hacks rather like the above will appear
if not enough useful functions are added.  We added an #expr function
on Wikipedia that originally supported mostly basic arithmetic.  IIRC,
we literally had people on Wikipedia manually writing out Taylor
series for sine and cosine to generate CSS that would position an
arbitrary number of things evenly spaced around circles of arbitrary
radius.  I wish I was kidding.  But I'm not, so be prepared.  :)
Eventually we caved and added a whole bunch of math functions so
people wouldn't have to resort to such hacks.

If the implementation burden isn't much greater, I think it would be a
good idea to define a bunch of standard math functions in calc() from
the get-go to avoid this kind of scenario.  Authors *will* want to use
min and max, and if they have to resort to a function like I gave
here, some of them will . . .
Received on Wednesday, 22 July 2009 01:01:47 GMT

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