Re: Syntax of new constraint proposal

On 5/19/14 6:00 AM, Harald Alvestrand wrote:
> In neither case are the semantics of "ideal" defined.
> [...]
> does it mean "I prefer values that tend towards this value
> rather than the "natural" direction (presumably higher), but any value
> in the range is OK",

That one I think. - I'm not on Sylvia's page here, but several people 
have mentioned "ideal", so let me answer with my idea of the definition, 
which I used a couple of months ago.

Extension 2 of that proposal ("ideal") still seems relevant if read in 
isolation, even though the surrounding syntax is not exactly the same. 
Excerpted from 
http://lists.w3.org/Archives/Public/public-media-capture/2014Mar/0083.html :

Extension #2: ideal
===================

dictionary ConstrainLongRange {
      long min;
      long max;
      long ideal;
};

dictionary ConstrainDoubleRange {
      double min;
      double max;
      double ideal;
};

Ideal expresses a target value within an acceptable range, with values
closer to the ideal more desirable.

For example, clients may use this to express preference for higher values:

    var constraints =
    {
        aspectRatio: 16/9,
        frameRate: { min: 60, max: 300, ideal: 300 },
    };
    navigator.getUserMedia(constraints, success, failure);

Only min and max need to be satisfied to satisfy a constraint, but
sources satisfied by the same range are individually ranked by their
proximity to the ideal. [2]

This example ranks 16/9 sources with frame-rates closest to 300hz
highest, followed by gradually lower frame-rate 16:9 ones down to 60hz,
followed by all other aspects 300hz and down.

---
[2] Ideal algorithm: For example, if three sources satisfy the frameRate
constraint above, the one with the lowest frame-rate among them gets 1/3
point, the middle one gets 2/3 points and the highest frame-rate one
gets one point.

(slides: 
http://lists.w3.org/Archives/Public/public-media-capture/2014Mar/att-0139/Constraints2014.pdf 
)

.: Jan-Ivar :.