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Re: Defining ConstraintSet and the constrainable algorithm in terms of it

From: Jim Barnett <1jhbarnett@gmail.com>
Date: Thu, 06 Feb 2014 18:52:39 -0500
Message-ID: <52F42047.6000502@gmail.com>
To: public-media-capture@w3.org
I don't think that this definition captures the interactions between 
constraints.  If aspectRatio and width have already been constrained, it 
is not enough to check that the requested value  for width is within the 
range specified by the relevant Capability. Your first four points are 
more precise than what's currently in the spec, but the last two have to 
be modified to talk of a set of property values satisfying a set of 

- Jim
On 2/6/2014 5:49 PM, Harald Alvestrand wrote:
> As promised, hashing out the language of ConstraintSet....
> First, an admission: I don't understand how initialization of complex 
> argument types in WebIDL is supposed to work.
> I tried to parse the WebIDL spec to figure out "here is how you 
> specify that an argument of type T can be constructed from a JS Object 
> O when O is passed as an argument to the function that takes an 
> argument of type T", but I did not find it. So I guess I'm left with 
> prose - and possibly supporting WebIDL.
> The algorithm I have in mind, which is a making-more-precise of 
> section 11.1.2 of the current (abbreviated) draft, says:
> WebIDL:
> typedef object ConstraintSet;
> The following operation is executed to figure out if the Constrainable 
> object O, which has capabilities CA, satisfies ConstraintSet C:
>    - For each immediate attribute A of C (as defined by HasOwnProperty):
>      - If N, the name of A, is not a member of CA, fail.
>      - If V, the value of A, cannot be interpreted as a 
> ConstraintValues, fail.
>      - If V does not permit any of the allowed values for CA(N), fail.
>      - Set the constraint of N in O to be the intersection of any 
> previous constraint
>        and V. If the result of this intersection is empty, fail.
>    - If satisfaction succeeded, return the newly-constrained object O.
> Here's where the now-deleted definition of ConstraintSet may come in 
> useful:
> In this algorithm specification, the access to C is done as if C had 
> the WebIDL definition:
> [NoInterfaceObject]
> interface ConstraintSetInternalRepresentation {
>     ConstraintValues getter (DOMString name);
> };
> (this may need extension. I'm not sure how. Or it may have no value, 
> and should be deleted.)
> Does this seem like a precise (and therefore implementable) algorithm?
> -- 
> Surveillance is pervasive. Go Dark.

Jim Barnett
Received on Thursday, 6 February 2014 23:53:16 UTC

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