Drivers: Introduce the Context Properties
The goal: allow accessing context dependent data, such as active scene camera
without linking to a specific scene data-block. This is useful in cases when,
for example, geometry node setup needs to be aware of the camera position.
A possible work-around without changes like this is to have some scene
evaluation hook which will update driver variables for the currently evaluating
scene. But this raises an issue of linking: it is undesirable that the asset
scene is linked to the shot file.
Surely, it is possible to have post-evaluation handler to clear the variables,
but it all starts to be quite messy. Not to mention possible threading
conflicts.
Another possibility of introducing a way to achieve the goal is to make it so
the dependency graph somehow parses the python expression where artists can
(and already are trying to) type something like:
depsgraph.scene.camera.matrix_world.col[3][0]
But this is not only tricky to implement properly and reliably, it hits two
limitations:
- Currently dependency graph can only easily resolve dependencies to a RNA
property.
- Some properties access which are valid in Python are not considered valid
RNA properties by the existing property resolution functions:
`camera.matrix_world[3][0]` is a valid RNA property, but
`camera.matrix_world.col[3][0]` is not.
Using driver variables allows to have visual feedback when the path resolution
fails, and there is no way to visualize errors in the python expression itself.
This change introduces the new variable type: Context Property. Using this
variable type makes allows to choose between Active Scene and Active View
Layer. These scene and view layer are resolved during the driver evaluation
time, based on the current dependency graph.
This allows to create a driver variable in the following configuration:
- Type: Context Property
- Context Property: Active Scene
- Path: camera.matrix_world[3][0]
The naming is a bit confusing. Tried my best to keep it clear keeping two
aspects in mind: using UI naming when possible, and follow the existing
naming.
A lot of the changes are related on making it so the required data is available
from the variable evaluation functions. It wasn't really clear what the data
would be, and the scope of the changes, so it is done together with the
functional changes.
It seems that there is some variable evaluation logic duplicated in the
`bpy_rna_driver.c`. This change does not change it. It is not really clear why
this separate code path with much more limited scope of supported target types
is even needed.
There is also a possible change in the behavior of the dependency graph: it
is now using ID of the resolved path when building driver variables. It used
to use the variable ID. In common cases they match, but when going into nested
data-blocks it is actually correct to use relation to the resolved ID. Not sure
if there was some code to ensure that, which now can be resolved. Also not sure
whether it is still needed to ensure the ID specified in the driver target is
build as well. Intuitively it is not needed.
Pull Request #105132
Use a shorter/simpler license convention, stops the header taking so
much space.
Follow the SPDX license specification: https://spdx.org/licenses
- C/C++/objc/objc++
- Python
- Shell Scripts
- CMake, GNUmakefile
While most of the source tree has been included
- `./extern/` was left out.
- `./intern/cycles` & `./intern/atomic` are also excluded because they
use different header conventions.
doc/license/SPDX-license-identifiers.txt has been added to list SPDX all
used identifiers.
See P2788 for the script that automated these edits.
Reviewed By: brecht, mont29, sergey
Ref D14069
This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.
This patch has been generated by P1561 followed by `make format`.
Differential Revision: https://developer.blender.org/D8466
BF-admins agree to remove header information that isn't useful,
to reduce noise.
- BEGIN/END license blocks
Developers should add non license comments as separate comment blocks.
No need for separator text.
- Contributors
This is often invalid, outdated or misleading
especially when splitting files.
It's more useful to git-blame to find out who has developed the code.
See P901 for script to perform these edits.
Drivers can use this to refer to the data which the driver is applied to,
useful for objects, bones, to avoid having to create a variable pointing to its self.
Support for driver variables that don't resolve to numbers, eg:
objects, bones, curves... etc.
Without this, Python expressions to access this data needed to use an absolute path from `bpy.data`,
however this is inconvenient, breaks easily (based on naming) and wouldn't set the dependencies correctly.
