Hi,
thank you for your answer, Sergey Sharybin.
To summarize:
MINVERSION refers to the minimum Blender version required to
read that particular file.
I thought about it and then I noticed the following:
Given the case I described before: Different struct layout in version
2.80 and 2.81. How does Blender in version 2.80 deal with the changed
struct layout in a file of version 2.81?
I could think of three options:
a) Future changes for 2.81 have already been considered in 2.80 and
conversion code exists in blenloader/intern/versioning_2_81.c in
blender 2.80. (probably not)
b) Blender 2.80 did not use those structs or attributes which
got moved in position, even though those already existed in
that version.
c) Those structs are used in memory only and get never stored in a
file, even though their type is declared in block DNA1.
This question is interesting, because (b) and (c) would also mean, that
(theoretically) data of a .blend file of v2.80 can also be stored in DNA
structs of v2.81 without conversion and without loss of information.
Thus, I could always use a pointer on struct of v2.81 and point it on
data of v2.80 and get the same (old) information. Is that correct?
This would have some implications I would like to clarify in my
documentation. That's why I try to get this right.
Kind regards
Holger Machens
On 30.11.19 19:58, Sergey Sharybin wrote:
Hi,
This is a part of forward compatibility (ability to open newer files in
older Blender versions).
Most of the time opening newer files does what you would expect, but in
others there is a huge data loss. For example, you can not open 2.8x files
in 2.7x because older Blender versions are not aware of Collections, and
old Layers are not stored in .blend file.
You can, however, open 2.82 and 2.81 files in Blender 2.80 (there might be
minor differences in final render due to changes in shaders, but nothing
too drastic).
Hence the miniversion of 2.80.
P.S. As far as i remember, it is only used to communicate users that the
file is too new, and no extra logic on read/write is dependent on the
miniversion.
On Sat, Nov 30, 2019 at 2:26 PM Holger Machens <[email protected]> wrote:
Hello folks!
TLDR question:
What is the meaning of the attributes
minversion and minsubversion in DNA
struct FileGlobal?
(ref: source/makesdna/DNA_fileglobal_types.h)
Too Long Explanation:
I've just updated my Java API (Java .Blend) to reflect recent DNA
changes in release 2.81-16. I've noticed, that BLENDER_MINVERSION still
refers to release 2.80-0 while some changes in the DNA of release 2.81-x
render older files incompatible on a binary level. For example some
attributes of structs in the DNA exchanged their position or new
attributes were added inbetween existing attributes, which also changes
the relative position of other attributes in the data structure. Thus,
you cannot just use a pointer to a C struct of version 2.81 to interpret
the data of a C struct in version 2.80. But it would have been possible
if attributes were only added to the end of a struct only for example.
I looked in the source code and read the recent manual but didn't find
an explanation regarding the meaning of MINVERSION and MINSUBVERSION.
According to my observations, I have to assume, that files in the range
from MINVERSION to VERSION are not meant to be binary compatible with
each other. On the other hand, Blender can read and translate Blender
files from much older versions than 2.80 for example. Thus, I wonder
what purpose the MINVERSION in the global files structure has. Is it
eventually going to be removed in future releases?
Thanks in advance
Holger Machens
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