[Development] [HiDPI] Rethinking the scaling algorithm

[Christoph Feck]

On 16.11.2016 17:22, Niccolò Belli wrote:
> Hi Morten,
> I'm sorry, I missed your reply.
>
>> RoundPreferFloor   Round up for .75 and higher
>> RoundPreferFloor is the new default. Do you think this is sufficient?
>
> qFloor would help for my monitor, of course.
>
> Unfortunately the default (RoundPreferFloor) wouldn't be enough, because
> my monitor is 282.42 PPI and 282.42/96=2.94
> Also RoundPreferFloor would break the 4K 27" monitor previously
> mentioned, because 161.18/96=1.6998
>
> I thought about a better default: round up for ratios lesser than 2 but
> always round down for ratios higher than 2.
>
> Such a way the new formula will work for both categories of monitors: it
> will basically keep the current algorithm but it will be a bit more
> conservative when handling extreme scalings (>=3x).
> The 4K 27" will get 2x scaling, the 13" 3200x1800 will get 2x scaling
> and both a 13" and a 15" 4K monitors will get 3x scaling. It seems
> perfect to me, especially if you plan to change the base DPI on a per-OS
> basis.

There is no perfect solution except to make sure the user can configure 
the pixmap scale (as he can configure the font size).

I have Firefox set to 1.5 scaling on a 163 DPI display. Neither 1, nor 2 
looks good.