Re: Bug 23935 - Proposal: New syntax for constraints

On 13/12/2013 4:06 PM, Jan-Ivar Bruaroey wrote:
> On 12/13/13 2:43 PM, cowwoc wrote:
>> I don't see how you could express the following constraints all at once:
>>
>>  1. For aspect ratio 4/3, require resolutions from 800x600 to
>>     1600x1200, prefer 1200x900
>>  2. For aspect ratio 16/9, require resolutions from 1280x720 to
>>     1920x1080, prefer 1600x900
>>
>
> Here you're saying "I must have these mandatory constraints OR these 
> other mandatory constraints". That's way beyond what you can express 
> today! That hardly seems fair. How come you didn't like my declarative 
> syntax then?

It's not about playing "fair". It's about testing how legitimate 
use-cases get expressed by the various proposals.

> With my original declarative syntax this is a piece of cake:
>
> [
>   { width: 1200, height: 900 },
>   { width: 1600, height: 900 },
>   {
>     aspect: { min: 1.33, max: 1.34 },
>     width: { min: 800, max: 1600 },
>     height: { min: 600, max: 1200 }
>   },
>   {
>     aspect: { min: 1.77, max: 1.78 },
>     width: { min: 1280, max: 1920 },
>     height: { min: 720, max: 1080 }
>   },
> ]
>
> Can I write you down as supporting it? ;-)

It's not clear to me how browser is meant to implement the above 
dictionary. I mean, does it scan from top to bottom and stop on the 
first match? From a readability point of view, I find the syntax ambiguous.

> The best you can do in our compromise proposal here based on the 
> loveable optional-array algorithm, is make this optional-only and 
> check the result from gUM() (because the optional-array algorithm is 
> procedural in nature). That version looks identical to the above btw.

I'm still operating under the premise that fingerprinting is not a 
problem. As such, I prefer the following code. Granted it's more 
verbose, but it's much easier to read and is obviously more flexible. 
You can also abstract common use-cases behind an API.

var modes = camera.getModes();
var resolution;
for (var i = 0; i<modes.length; ++i)
{
   var mode = modes[i];
   if (mode.aspectRatio > 1.33 && mode.aspectRatio < 1.34)
   {
     if (!mode.supportsResolution(800, 600) || 
!mode.supportsResolution(1600, 1200))
       continue;
     if (mode.supportsResolution(1200, 900))
       resolution = { width: 1200, height: 900 };
     else
       resolution = mode.maximumResolution();
     break;
   }
   else
   {
     if (!mode.supportsResolution(1280, 720) || 
!mode.supportsResolution(1920, 1080))
       continue;
     if (mode.supportsResolution(1600, 900))
       resolution = [1600, 900];
     else
       resolution = mode.maximumResolution();
     break;
   }
}
if (!resolution)
{
   failGracefully();
   return;
}
var properties = { width: resolution.width, height: resolution.height, 
frameRate: 20 };// specific values that the device must support (ranges 
are not accepted)
getUserMedia(properties, onSuccess, onFailure);

Gili