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< Dependency graph Copy-on-Write >
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This is an initial commit of Copy-on-write support added to dependency graph.
Main priority for now: get playback (Alt-A) and all operators (selection,
transform etc) to work with the new concept of clear separation between
evaluated data coming from dependency graph and original data coming from
.blend file (and stored in bmain).
= How does this work? =
The idea is to support Copy-on-Write on the ID level. This means, we duplicate
the whole ID before we cann it's evaluaiton function. This is currently done
in the following way:
- At the depsgraph construction time we create "shallow" copy of the ID
datablock, just so we know it's pointer in memory and can use for function
bindings.
- At the evaluaiton time, the copy of ID get's "expanded" (needs a better
name internally, so it does not conflict with expanding datablocks during
library linking), which means the content of the datablock is being
copied over and all IDs are getting remapped to the copied ones.
Currently we do the whole copy, in the future we will support some tricks
here to prevent duplicating geometry arrays (verts, edges, loops, faces
and polys) when we don't need that.
- Evaluation functions are operating on copied datablocks and never touching
original datablock.
- There are some cases when we need to know non-ID pointers for function
bindings. This mainly applies to scene collections and armatures. The
idea of dealing with this is to "expand" copy-on-write datablock at
the dependency graph build time. This might introduce some slowdown to the
dependency graph construction time, but allows us to have minimal changes
in the code and avoid any hash look-up from evaluation function (one of
the ideas to avoid using pointers as function bindings is to pass name
of layer or a bone to the evaluation function and look up actual data based
on that name).
Currently there is a special function in depsgraph which does such a
synchronization, in the future we might want to make it more generic.
At some point we need to synchronize copy-on-write version of datablock with
the original version. This happens, i.e., when we change active object or
change selection. We don't want any actual evaluation of update flush happening
for such thins, so now we have a special update tag:
DEG_id_tag_update((id, DEG_TAG_COPY_ON_WRITE)
- For the render engines we now have special call for the dependency graph to
give evaluated datablock for the given original one. This isn't fully ideal
but allows to have Cycles viewport render.
This is definitely a subject for further investigation / improvement.
This call will tag copy-on-write component tagged for update without causing
updates to be flushed to any other objects, causing chain reaction of updates.
This tag is handy when selection in the scene changes.
This basically summarizes ideas underneath this commit. The code should be
reasonably documented.
Here is a demo of dependency graph with all copy-on-write stuff in it:
https://developer.blender.org/F635468
= What to expect to (not) work? =
- Only meshes are properly-ish aware of copy-on-write currently, Non-mesh
geometry will probably crash or will not work at all.
- Armatures will need similar depsgraph built-time expansion of the copied
datablock.
- There are some extra tags / relations added, to keep things demo-able but
which are slowing things down for evaluation.
- Edit mode works for until click selection is used (due to the selection
code using EditDerivedMesh created ad-hoc).
- Lots of tools will lack tagging synchronization of copied datablock for
sync with original ID.
= How to move forward? =
There is some tedious work related on going over all the tools, checking
whether they need to work with original or final evaluated object and make
the required changes.
Additionally, there need synchronization tag done in fair amount of tools
and operators as well. For example, currently it's not possible to change
render engine without re-opening the file or forcing dependency graph for
re-build via python console.
There is also now some thoughts required about copying evaluated properties
between objects or from collection to a new object. Perhaps easiest way
would be to move base flag flush to Object ID node and tag new objects for
update instead of doing manual copy.
here is some WIP patch which moves such evaluaiton / flush:
https://developer.blender.org/F635479
Lots of TODOs in the code, with possible optimization.
= How to test? =
This is a feature under heavy development, so obviously it is disabled by
default. The only reason it goes to 2.8 branch is to avoid possible merge
hell.
In order to enable this feature use WITH_DEPSGRAPH_COPY_ON_WRITE CMake
configuration option.
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This way everyone can benefit from it, not only dependency graph.
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This moves selectability/visibility flag flush from some hardcoded
places in the code to depsgraph. This way it is possible to simply
tag depsgraph to update those flags and rest it'll do on its own.
Using depsgraph for such flush is an overkill: those flags are fully
static and can not be animated, so it doesn't really make sense to
hook only those to depsgraph.
However, in the future we will have overrides on collections, which
ideally would need to be animatable and drivable and easiest way
to support this is to do this on depsgraph level, so it ensures
proper order of evaluation for animation and drivers. And it seems
logical to do both overrides and flags flush from depsgraph from
this point of view.
This commit also includes the evaluation of IDProperty for collections,
which basically are just another form of override. So once we implement
the other kind of overrides the flushing and collection evaluation won't
change.
Patch by Sergey Sharybin and Dalai Felinto
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Now we have no remaining WITH_LEGACY_DEPSGRAPH in the code.
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This way it's much easier to grasp what the graph actually contains.
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Those routines are rather big and started to be annoying to have
one big file.
Should be no functional changes.
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This is mainly a maintenance commit which was aimed to make work with
this module more pleasant and solve such issues as:
- Annoyance with looong files, which had craftload in them
- Usage of STL for the data structures we've got in BLI
- Possible symbol conflicts
- Not real clear layout of what is located where
So in this commit the following changes are done:
- STL is prohibited, it's not really predictable on various compilers,
with our BLI algorithms we can predict things much better.
There are still few usages of std::vector, but that we'll be
solving later once we've got similar thing in BLI.
- Simplify foreach loops, avoid using const_iterator all over the place.
- New directory layout, which is hopefully easier to follow.
- Some files were split, some of them will be split soon.
The idea of this is to split huge functions into own files with
good documentation and everything.
- Removed stuff which was planned for use in the future but was never
finished, tested or anything.
Let's wipe it out for now, and bring back once we really start using
it, so it'll be more clear if it solves our needs.
- All the internal routines were moved to DEG namespace to separate
them better from rest of blender.
Some places now annoyingly using DEG::foo, but that we can olve by
moving some utility functions inside of the namespace.
While working on this we've found some hotspot in updates flush, so
now playback of blenrig is few percent faster (something like 96fps
with previous master and around 99-100fps after this change).
Not saying it's something final, there is still room for cleanup and
API simplification, but those might happen as a regular development
now without doing any global changes.
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Previously several areas were calling TEST_SHARED_PTR_SUPPORT and
TEST_UNORDERED_MAP_SUPPORT which isn't that bad on it's own but
was causing some quite verbose output with same information line
printed multiple times. additionally, what's more worse, define flags
for Ceres were duplicated in main CMakeLists and Ceres's CMakeLists.
Now we've got a single place where checks for those classes are
happening and other areas are simply checking for variables set by
those check macros, keeping CMake output clean and nice.
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Cases like using subsurfed object as a boolean operand can't be evaluated
on GPU and needs to have all the CCG on CPU.
This commit resolves existing configuration to survive, but new configurations
would need to have some sort of forced object update so all the data is being
moved on CPU if it was previously on GPU.
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This commit integrates the work done so far on the new dependency graph system,
where goal was to replace legacy depsgraph with the new one, supporting loads of
neat features like:
- More granular dependency relation nature, which solves issues with fake cycles
in the dependencies.
- Move towards all-animatable, by better integration of drivers into the system.
- Lay down some basis for upcoming copy-on-write, overrides and so on.
The new system is living side-by-side with the previous one and disabled by
default, so nothing will become suddenly broken. The way to enable new depsgraph
is to pass `--new-depsgraph` command line argument.
It's a bit early to consider the system production-ready, there are some TODOs
and issues were discovered during the merge period, they'll be addressed ASAP.
But it's important to merge, because it's the only way to attract artists to
really start testing this system.
There are number of assorted documents related on the design of the new system:
* http://wiki.blender.org/index.php/User:Aligorith/GSoC2013_Depsgraph#Design_Documents
* http://wiki.blender.org/index.php/User:Nazg-gul/DependencyGraph
There are also some user-related information online:
* http://code.blender.org/2015/02/blender-dependency-graph-branch-for-users/
* http://code.blender.org/2015/03/more-dependency-graph-tricks/
Kudos to everyone who was involved into the project:
- Joshua "Aligorith" Leung -- design specification, initial code
- Lukas "lukas_t" Toenne -- integrating code into blender, with further fixes
- Sergey "Sergey" "Sharybin" -- some mocking around, trying to wrap up the
project and so
- Bassam "slikdigit" Kurdali -- stressing the new system, reporting all the
issues and recording/writing documentation.
- Everyone else who i forgot to mention here :)
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