Previously it was possible to run into situation when armature is constructed prior to
objects which are used for it's constraints. This was causing wrong scene evaluation.
Now we create placeholders for objects used by armature in case they don't have ID node
yet, which ensures we have proper mapping from original to copy-on-write ID pointer.
This shows the bug when IK solver doesn't update reliably when targeted an external
object and when that object is handled by build_object() after the armature.
Previously tagging particle settings for update will iterate over all objects and
all their particle system to see whether something needs an update or not. Now we
put ParticleSettings as an ID to the dependency graph, so tagging it for update
will nicely flush updates to all dependent particle systems.
Current downside of this is that due to limitation of flush routines it will cause
some extra particle system re-evaluation when it technically not needed, and what's
more annoying currently it will discard point caches more often.
However, this is a good and simple demonstration case to improve tagging/flushing
system to accommodate for such cases (similar issues happens with CoW and shading
components). So let's try to find some generic solution to the problem!
This replaces usage of generic PLACEHOLDEWR with string lookup with more
explicit opcode. This should make it faster to build dependency graph by
avoiding string comparisons when it's not needed.
There should be no user measurable different.
This commit makes simple cases to work, for example:
- IK solver to an external object
- Object with Armature modifier, "parented" to the deforming armature
(via animation).
More complicated setups (like agent rig) are crashing still.
UVs need specific data in the VBO, which is not computed unless the
shaders assigned to the mesh actually use UVs. When adding UVs to the
shader, the VBOs were not being recomputed to include the required data.
This adds a DEG relation between the shader and the mesh, and recomputes
the required data if the shader changed.
Thanks Sergey, for all the DEG stuff...
< 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.
Avoids using copy-constructor invoked every time we pass function
to the builder functions.
Should lower number of CPU ticks spent during DEG construction.
Was rather weird and only used for time source. It is simpler to make depsgraph
to keep track of time source directly.
No need to introduce extra entitites without actual need.
We need to traverse the same exact objects for both nodes and relationship
builder. We were using FOREACH_SCENE_OBJECT for relationships, which
would lead to plenty of warnings in multiple situations.
In the future we will need to change this to build the depsgraph
relations and nodes to one single render_layer.
Fix T51780: If an object is in two collections and I do a full copy of
scene things go bad
Probes were completely out of depsgraph, so tagging them could not work at all.
For now using some placeholder operations just to ensure order of updates.
Use indirect access to it via object.
It was already flushing from base to object, now we can avoid such flushing.
Still weird to have selection color filled in by dependency graph, but now
there is no synchronization going on at least.
Was internally a no-op operation, which only caused extra work
to be done during depsgrpah traversal and evaluation, without
making any measurable improvement.
It was never actually used apart from being stored at a construciton time.
This caused some redundancy and ncertanty about which relation type to use
during construciton (often existing types were not close enough to particular
use case).
This way we always have predictable behavior, especially from the
performance point of view. Additionally, if some bottleneck is found
in stack implementation it'll be easier for us to address.
Was preventing update in 3DView etc. when changing something in the
World's NodeTree, especially annoying in blender2.8 branch (since legacy
depsgraph has been removed there), but also affecting master.
