The use case for this will be to detech which screen is connected to
an output from the screen rules.
It is in millimeters because this is what the output provides and in
inches because the DPI is based on that unit and screens are sold with
the size in inches on the box.
Identical viewports are already handled before getting into Lua,
but sometime xrandr gives another viewport that encompass all
others. It has to be removed.
When the screens are created from the viewport in Lua, the signal is
sent too early and the DPI and outputs have not yet been added. This
cause the `connect_for_each_screen` callbacks to be called with a
partially initialized screen object. It also causes the drawables to be
repainted too early.
CAPI now emits "_added" and "awful.screen" takes care of emitting
"added".
With this, there is plenty of palces where the DPI can be set before
those signals are sent. This allows wallpaper with the proper DPI to
work with screens created using `fake_add`. In turn, this will allow
screen rules to control the DPI. In "the past", the DPI used for those
handler was the native DPI of the screen with no opportunity to change
it before hand.
Add `dpi.lua` to config.ld even if it isn't added yet. This is
because the way the test run has it cached in the build dir. A full
rebuild would take too long and timeout on travis for semi-large PRs.
Emmanuel Lepage Vallee