[Development] resolution independence (was Re: Retina display support)

[Niels Ole Salscheider]

> Sure.  The question is, is that want the designer wants?  What was the
> intent, and why?
> 
> Do they want it 20mm because it looks good? Where? On a hand-held device? On
> a desktop? On a projector?  Is 20mm because they want to guarantee an easy
> touch target? Or easy to see from a particular distance?

We could introduce some "size mode" property that can either be "real" or 
"perceived".

In the former case, 20mm would always be 20mm on the screen.
For the latter case, a scaling factor would be used, taking the viewing 
distance into account. This scaling factor should be used to keep the visual 
angle constant, assuming that the given 20mm specify the size on screen for a 
"standard" reading distance of 40cm.
This scaling factor would be provided by the operating system, either directly 
or as virtual dpi/viewing distance/...

The second mode should probably be the default for user interfaces, while the 
first mode should be used for touch buttons, rulers, ...

We could also add a third "mixed" mode that would choose the larger value of 
the first two modes for the screen size, as Tony proposed.

An alternative to introducing different size modes would be to use different 
units for "real mm" and "perceived mm", but that might be confusing.

Regards,

Ole
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