output: automatically compute scaling factor
phoc currently defaults to unity scaling, unless the corresponding
output configuration contains a scale value. Whenever the physical
size of the output is available, we could actually calculate this value
in order to reach the best apparent DPI. This will allow distributions
to get rid of device-specific config files.
This gives good results in the following cases (tested on all devices I had on hand):
| Device | Mode | Hor. DPI | Vert. DPI | Scale |
|---|---|---|---|---|
| OnePlus 6 | 1080 x 2280 | 403.418 | 399.393 | 3 |
| Poco F1 | 1080 x 2246 | 403.418 | 419.473 | 3 |
| PinePhone | 720 x 1440 | 268.941 | 268.941 | 2 |
| Librem 5 | 720 x 1440 | 281.354 | 281.354 | 2 |
| PineTab | 800 x 1280 | 150.518 | 149.825 | 1 |
| Surf Pro 3 | 2160 x 1440 | 219.456 | 215.153 | 2 |
| Surf Go 2 | 1920 x 1080 | 221.673 | 216.747 | 2 |
| Nexdock 360 | 1920 x 1080 | 168.166 | 161.365 | 1 |
| STM32 dev board | 480 x 800 | 236.279 | 234.462 | 1.25 |