From: "Carlo E. Prelz" <fluido@...>
Date: 2013-04-06T03:39:50+09:00
Subject: Re: Change fond color based on dark/light bg [Sinatra,HAML,CSS]

	Subject: Change fond color based on dark/light bg [Sinatra,HAML,CSS]
	Date: sab 06 apr 13 02:54:01 +0900

Quoting Panagiotis Atmatzidis (atma@convalesco.org):

> The problem that the background changes in colors. It's bright
> colored by day and dark colored by night, so I need to find a way to
> change font-colors based on the background. I'm using HAML, CSS and
> Sinatra. 
> 
> Can you think of any way of doing something like that?  Apparently I
> can't do that using CSS or SASS (not 100% sure though).
> 
> Is there any way I can have ruby read the BG color and then decide
> if I'll display the 'weather_light' route or the 'weather_dark'
> sinatra route?

You can extract the average luminosity from an image - just decompres
it, then sum all the bytes and divide by the number of bytes - you'll
have a number between 0 and 255. Lower than  128 -> weather_dark,
else weather_light.

Of course you should get a copy of the image yourself, in order to
process it. It is not clear from your mail if you serve these
backgrounds yourself or you redirect elsewhere. If you redirect, you
can always have a background task that runs maybe once per hour, gets
retrieves a copy of the image and sets a variable that is accessible
within Sinatra (possibly a global variable) with the current
luminosity.

Carlo

-- 
  *         Se la Strada e la sua Virtu' non fossero state messe da parte,
* K * Carlo E. Prelz - fluido@fluido.as             che bisogno ci sarebbe
  *               di parlare tanto di amore e di rettitudine? (Chuang-Tzu)