Define the fitness distance for all required constrains.

[eehakkin]

This CL defines the fitness distance also for required constrains whose
value contains a member named 'ideal' in addition to members named
'exact', 'max' and/or 'min'.

Lets take a width constraint {ideal: 1920, min: 320} as an example and lets assume that the browser supports the constraint and that there are settings dictionaries which satisfy the constraint (so fitness distance algorithm steps 1 and 2 can be ignores).
Then,

• the step 3 does not apply because the constraint is required (has 'min'),
• the step 4 does not apply because the ideal value is specified, and
• the steps 5 and 6 do not apply because the constraint is not non-required but required,

thus the fitness distance is undefined.

Clearly, the step 5 should apply and the fitness distance should be positive infinity for settings dictionaries with width less than 320, 0 for settings dictionaries with width of 1920 and |actual - 1920| / max(|actual|, 1920) for other settings dictionaries.

[youennf]

Booleans are also not covered.
It might be good to add a catch-them-all case where the distance would be 0.

[youennf]

Would be good to add some tests and see what implementations are doing.

[henbos]

@guidou Can you add your two cents?

[guidou]

I think this change is correct (wasn't the spec written this way in the past?), but booleans need to be added to step 6.

[eehakkin]

I think this change is correct (wasn't the spec written this way in the past?), but booleans need to be added to step 6.

Done.

[youennf]

I am pretty sure this is inline with what all implementations are doing but it is worth checking.
Can we write a WPT test checking exactly that something like getUserMedia({ video : { min : 160, ideal : 320 }) actually returns a video track of width 320 (and not 160 or the default 640 that some implementations may use)?

[eehakkin]

I am pretty sure this is inline with what all implementations are doing but it is worth checking.
Can we write a WPT test checking exactly that something like getUserMedia({ video : { min : 160, ideal : 320 }) actually returns a video track of width 320 (and not 160 or the default 640 that some implementations may use)?

Done in web-platform-tests/wpt#25493