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)
