This is to make it possible, in the future, to create multiple instances
of `NotCurses` for multiple terminals. The first instance of
`NotCurses` becomes the default one, so that any instances of other
classes that aren't explicitly created with a pointer to another
`NotCurses` instance still work as expected.
Note that currently trying to call `notcurses_init` twice results in the
following error for me:
0x55555559bfc0 is already registered for signals
Couldn't drop signals: 0x55555559bfc0 != 0x5555555b6720
terminate called after throwing an instance of 'ncpp::init_error*'
Program received signal SIGABRT, Aborted.
The error is signalled by `setup_signals` and the pointer shown in the
message points to the first `struct notcurses` instance created.
Nick prefers error handling based on exceptions in all cases, while I
prefer to save exception handling for truly exceptional situations -
function parameter validation and class constructor. However, there's no
need to not support both approaches, to be chosen at the discretion of
the developer.
NCPP follows RAII and all classes throw exceptions from their
constructors in case they cannot initialize properly. Likewise,
functions taking pointers that are required validate them and throw
exceptions whenever the requirement isn't met.
This commit goes one step further in that it enables optional validation
of notcurses function return values and throwing an
exception (`ncpp::call_error`) should the function signal an error. This
is disabled by default but it can be enabled by defining the
`NCPP_EXCEPTIONS_PLEASE` macro (preferably on the command line or
before *each* inclusion of any NCPP headers).
Out of necessity, this breaks the ABI (plus I found a handful of minor
issues in the code), but I think it's worth having this support in
place.
Added:
* Plane: gradient (`ncplane_gradient`)
* Plane: gradient_sized (`ncplane_gradient_sized`)
* NotCurses: drop_planes (`ncplane_drop_planes`)
* NcReel: constructor which takes `Plane&`
* Visual: constructors which take `Plane const*`, `Plane&` and `Plane const&`)
* ncpp_build: a nonsensical "demo" which exists purely to test whether
the C++ builds and does absolutely nothing interesting.
Broke:
* All exceptions throw temporary objects instead of allocated
instances. Less typing in `catch` :P (and more conventional)
