While branching on a compiler is rather common, checking a particular
compiler version should be needed only rarely. Thus minimize use of such
macros to make them easier to grep for.
As implementation-specific index types cause the index buffer to be
strided. which is not allowed by default, these work only if
InterleaveFlag::PreserveStridedIndices is set. Originally I thought
about straight-out disallowing implementation-specific types here,
unfortunately that broke some valid use cases so I backtracked on that
decision.
In the future I might change the default to preserve
implementation-specific indices with sane strides (i.e., positive powers
of 2), but that will only be done once similar treatment is finished for
attributes (currently zero and negative strides are just disallowed
completely).
Otherwise it makes a tightly-packed copy. This also means that arbitrary
padding before/after the index buffer is preserved only in case it would
mean the data can be transferred without a copy -- otherwise it's faster
to just drop the padding and copy only the used part.
I tried, I really did, but the downsides eventually just outweighed the
potential of this feature and I gave up. May try to tackle this again in
the future, but not now.
This took me quite a while to realize -- not always it's desirable to
have the original layout unconditionally preserved, especially if for
example filtering a MeshData to just a subset of attributes.
Haha, I even had a TODO here. An exception in this case is when the mesh
is already interleaved -- then the layout is kept intact and thus it's
not needed to know what vertex format sizes to repack.
Originally this was done in order to make handling of deserialized data
much simpler (as for those attributes also need to only contain an
offset into some unknown data array), but seems this could be very
useful elsewhere as well -- for example when the layout is known
beforehand but the actual data not yet -- such as in the Line and
Gradient primitives (going to switch them to this in the next commit).
What still unfortunately has to be known in advance is the actual vertex
count (as supplying it directly to MeshData would mean adding 6 new
constructor overloads, and there's enough of those already). Might
revisit later.
This was originally meant to be an interleave() that operates on
MeshData, but later I realized I need the same logic in duplicate(), so
turned it into a private function. Now I am pretty sure I'll be using
this function in *many* importer plugins :D
It makes sense, but this ordering also helps to avoid bug in Doxygen
1.8.6+ which merges next non-xrefitem section with the previous one (so
e.g. the TODO list contained the following @see block, which is not
desired).