Framebuffer::attach*() doesn't need the target at all (meaning the
attachment will be used for both reading and drawing), another
misunderstanding on my side.
Now the extension is used on all places where it can be used (except for
unimplemented features).
It prevents unwanted implicit conversions from e.g. nullptr to Camera,
Vector2 to Physics::Point etc. By making all the constructors explicit
it is easier to routinely add the keyword to all new classes instead of
thinking about cases when to add and when not to.
Viewport position and size is managed separately for each framebuffer
and glViewport() is called in bind() (and also from setViewport(), if
the framebuffer is currently bound) if the viewport differs from
current state. If used only one framebuffer size through whole
application lifetime, glViewport() doesn't need to be called at all.
Default framebuffer is now accessible throught defaultFramebuffer global
variable, named framebuffers are handled the same way as before. All
operations (clear, setViewport, blit, read) now are member functions
so they cannot be mistakenly used when unwanted framebuffer is bound.
Further rework (DSA, state tracking...) is on the way.
Vladimír Vondruš