Previously, the data-block dependencies were always detected in
`update_depsgraph` in `MOD_nodes.cc`. This would only be called when something
called `DEG_relations_tag_update` before. We don't want to trigger a depsgraph
rebuild after each operation in the node editor, as that would be expensive.
However, that also meant that we often had to add data-block dependencies that
are not actually used, but might be used if the user changed e.g. a link. A
typical example for that is a object socket that has a default value, but the
socket is also linked.
Now, the dependencies referenced by the node tree are collected by the node tree
update code which runs after all changes. This way we can detect whether the
dependencies have changed. Only if they have changed, a depsgraph rebuild is
triggered. This now allows also taking into account the mute status of nodes and
whether an input is linked.
There are still more things that could be taken into account. Most obviously
whether a node is connected to an output. This can be done later. The most
tricky aspect here is probably that we also have to consider all viewer nodes as
output, because at the time the node runs, it's not known which viewer will
actually be used (which depends on other editors).
This also cleans up some special cases we had for e.g. the scene time node where
we always had to trigger a depsgraph rebuild when it was added/removed because
of its time dependence. This is now part of a more general system.
This fixes#109219.
Pull Request: https://projects.blender.org/blender/blender/pulls/131446
NOTE: This also required some changes to Cycles code itself, who is now
directly including `BKE_image.hh` instead of declaring a few prototypes
of these functions in its `blender/utils.h` header (due to C++ functions
names mangling, this was not working anymore).
Pull Request: https://projects.blender.org/blender/blender/pulls/130174
This refactors the lifetime analysis of anonymous attributes in geometry nodes.
The refactor has a couple of goals:
* Use a better and simpler abstraction that can be used when building the
lazy-function graph. We currently have a bunch of duplicate code to handle
"field source" and "caller propagation" attributes. This is now unified so
that one only has to worry about one kind of "reference sets".
* Make the abstraction compatible with handling bundles and closures in case we
want to support them in the future. Both types can contain geometries and
fields so they need to be taken into account when determining lifetimes.
* Make more parts independent of the concept of "anonymous attributes". In
theory, there could be more kinds of referenced data whose lifetimes need to
be managed. I don't have any concrete plans for adding any though.
At its core, deterministic anonymous attributes still work the same they have
been since they became deterministic [0]. Even the generated lazy-function graph
is still pretty much or even exactly the same as before.
The patch renames `AnonymousAttributeSet` to the more general
`GeometryNodesReferenceSet` which is more. This also makes more places
independent of the concept of anonymous attributes. Functionally, this still the
same though. It's only used in the internals of geometry nodes nowadays. Most
code just gets an `AttributeFilter` that is based on it.
[0]: https://archive.blender.org/developer/D16858
Pull Request: https://projects.blender.org/blender/blender/pulls/128667
Adds support for the "Menu" socket type in for-each-element zones. This
only includes field inputs and their matching per-element values, but
not outputting attributes of type Menu (Menu attributes are not
generally supported at this point).
A dedicated enum propagation function is added for the zone input node.
This isn't technically necessary: the first 2 inputs and outputs should
be ignored but are not menus anyway. However, this is clearer and
provides a place for future changes.
Pull Request: https://projects.blender.org/blender/blender/pulls/128106
This adds a new type of zone to Geometry Nodes that allows executing some nodes
for each element in a geometry.
## Features
* The `Selection` input allows iterating over a subset of elements on the set
domain.
* Fields passed into the input node are available as single values inside of the
zone.
* The input geometry can be split up into separate (completely independent)
geometries for each element (on all domains except face corner).
* New attributes can be created on the input geometry by outputting a single
value from each iteration.
* New geometries can be generated in each iteration.
* All of these geometries are joined to form the final output.
* Attributes from the input geometry are propagated to the output
geometries.
## Evaluation
The evaluation strategy is similar to the one used for repeat zones. Namely, it
dynamically builds a `lazy_function::Graph` once it knows how many iterations
are necessary. It contains a separate node for each iteration. The inputs for
each iteration are hardcoded into the graph. The outputs of each iteration a
passed to a separate lazy-function that reduces all the values down to the final
outputs. This final output can have a huge number of inputs and that is not
ideal for multi-threading yet, but that can still be improved in the future.
## Performance
There is a non-neglilible amount of overhead for each iteration. The overhead is
way larger than the per-element overhead when just doing field evaluation.
Therefore, normal field evaluation should be preferred when possible. That can
partially still be optimized if there is only some number crunching going on in
the zone but that optimization is not implemented yet.
However, processing many small geometries (e.g. each hair of a character
separately) will likely **always be slower** than working on fewer larger
geoemtries. The additional flexibility you get by processing each element
separately comes at the cost that Blender can't optimize the operation as well.
For node groups that need to handle lots of geometry elements, we recommend
trying to design the node setup so that iteration over tiny sub-geometries is
not required.
An opposite point is true as well though. It can be faster to process more
medium sized geometries in parallel than fewer very large geometries because of
more multi-threading opportunities. The exact threshold between tiny, medium and
large geometries depends on a lot of factors though.
Overall, this initial version of the new zone does not implement all
optimization opportunities yet, but the points mentioned above will still hold
true later.
Pull Request: https://projects.blender.org/blender/blender/pulls/127331
This implements the `Warning` node that allows node groups to communicate
expectations about input values to the user.
By default, the `Warning` node is only evaluated if the node group that contains
it is evaluated in any way. This is better than always evaluating it, because
that could trigger lots of unnecessary evaluation in parts of the potentially
large node tree which should be ignored. In this basic mode, the output of the
node should not be connected to anything and it must not be in a zone.
For more fine-grained control for when the `Warning` node should be evaluated,
one can use the boolean output which is just a pass-through of the `Show` input.
If this output is used, the `Warning` node will only be evaluated if its output
is used. A simple way to use it is to control a Switch node with it that e.g.
"disables" a specific output when the inputs are invalid. In this case, the
`Warning` node may also be in a zone.
The node allows the user to choose between 3 severity levels: Error, Warning and
Info. Those are the same levels that we use internally. Currently, the error and
warning mode are pretty much the same, but that may change in the future.
Pull Request: https://projects.blender.org/blender/blender/pulls/125544
Previously, the inferencing result was only stored in the socket shape.
However, that was conflicting with experiments where the socket shape and
the field state was not related.
Use snake style naming for all the kernel nodes functions.
Omit kernel prefix in the names since of the using namespace.
Use full forms of the terms
('iter' -> 'iterator', 'ntree' -> 'node_tree', 'rem' -> 'remove', ...).
Pull Request: https://projects.blender.org/blender/blender/pulls/126416
Previously, values for `ID.flag` and `ID.tag` used the prefixes `LIB_` and
`LIB_TAG` respectively. This was somewhat confusing because it's not really
related to libraries in general. This patch changes the prefix to `ID_FLAG_` and
`ID_TAG_`. This makes it more obvious what they correspond to, simplifying code.
Pull Request: https://projects.blender.org/blender/blender/pulls/125811
This adds support for attaching gizmos for input values. The goal is to make it
easier for users to set input values intuitively in the 3D viewport.
We went through multiple different possible designs until we settled on the one
implemented here. We picked it for it's flexibility and ease of use when using
geometry node assets. The core principle in the design is that **gizmos are
attached to existing input values instead of being the input value themselves**.
This actually fits the existing concept of gizmos in Blender well, but may be a
bit unintutitive in a node setup at first. The attachment is done using links in
the node editor.
The most basic usage of the node is to link a Value node to the new Linear Gizmo
node. This attaches the gizmo to the input value and allows you to change it
from the 3D view. The attachment is indicated by the gizmo icon in the sockets
which are controlled by a gizmo as well as the back-link (notice the double
link) when the gizmo is active.
The core principle makes it straight forward to control the same node setup from
the 3D view with gizmos, or by manually changing input values, or by driving the
input values procedurally.
If the input value is controlled indirectly by other inputs, it's often possible
to **automatically propagate** the gizmo to the actual input.
Backpropagation does not work for all nodes, although more nodes can be
supported over time.
This patch adds the first three gizmo nodes which cover common use cases:
* **Linear Gizmo**: Creates a gizmo that controls a float or integer value using
a linear movement of e.g. an arrow in the 3D viewport.
* **Dial Gizmo**: Creates a circular gizmo in the 3D viewport that can be
rotated to change the attached angle input.
* **Transform Gizmo**: Creates a simple gizmo for location, rotation and scale.
In the future, more built-in gizmos and potentially the ability for custom
gizmos could be added.
All gizmo nodes have a **Transform** geometry output. Using it is optional but
it is recommended when the gizmo is used to control inputs that affect a
geometry. When it is used, Blender will automatically transform the gizmos
together with the geometry that they control. To achieve this, the output should
be merged with the generated geometry using the *Join Geometry* node. The data
contained in *Transform* output is not visible geometry, but just internal
information that helps Blender to give a better user experience when using
gizmos.
The gizmo nodes have a multi-input socket. This allows **controlling multiple
values** with the same gizmo.
Only a small set of **gizmo shapes** is supported initially. It might be
extended in the future but one goal is to give the gizmos used by different node
group assets a familiar look and feel. A similar constraint exists for
**colors**. Currently, one can choose from a fixed set of colors which can be
modified in the theme settings.
The set of **visible gizmos** is determined by a multiple factors because it's
not really feasible to show all possible gizmos at all times. To see any of the
geometry nodes gizmos, the "Active Modifier" option has to be enabled in the
"Viewport Gizmos" popover. Then all gizmos are drawn for which at least one of
the following is true:
* The gizmo controls an input of the active modifier of the active object.
* The gizmo controls a value in a selected node in an open node editor.
* The gizmo controls a pinned value in an open node editor. Pinning works by
clicking the gizmo icon next to the value.
Pull Request: https://projects.blender.org/blender/blender/pulls/112677
Extract
- Add to Quick Favorites tooltip.
- "Mask", the name of a newly created mask (DATA_).
- "New" in the context of the new mask ID button.
- A few strings using BLI_STR_UTF8_ defines were not extracted.
Take the special characters out of the translation macros.
- "External" menu items from the filebrowser's Files context
menu (right-click on a file). These items were already extracted,
but not translated.
Improve
- Separate formatted error message "%s is not compatible with
["the specified", "any"] 'refresh' options" into two messages.
Disambiguate
- Use Action context for new F-modifiers' names. This is already used
for the "type" operator prop.
- Translate ImportHelper's default confirmation text using the
Operator context, as it uses the operator name which is extracted
with this context.
- "Scale" can be a noun, the scale of something, or a verb, to scale
something. The latter mostly uses the Operator context, so apply
this context to verbs, and the default contexts to nouns.
- "Scale Influence" can mean "Influence on Scale" (tracking
stabilization) and "to Scale the Influence" (dynamic paint canvas).
- "Object Line Art" as type of Line Art to add, as opposed to the
active object's Line Art settings.
- Float to Integer node: use NodeTree context for the node label, as
this is already extracted and used for the enum.
Do not translate
- Sequencer labels containing only a string formatting field.
Some issues reported by Gabriel Gazzán and Ye Gui.
Pull Request: https://projects.blender.org/blender/blender/pulls/122283
Blender shows invalid links in red in the node editor. However, it's not always
obvious why some links don't work, especially for beginners. This patch adds
additional information for every invalid link on the node that it links to.
The following error messages are added:
* Invalid link because of missing implicit conversions.
* Link cycle in node tree.
* A link from a field to a socket that does not support fields.
* Using the same menu on multiple Menu Switch nodes.
Currently, there are some per tree-type special cases in the link validation code.
In the future, this should be moved to tree type specific callbacks.
Pull Request: https://projects.blender.org/blender/blender/pulls/121976
Move all header file into namespace.
Unnecessary namespaces was removed from implementations file.
Part of forward declarations in header was moved in the top part
of file just to do not have a lot of separate namespaces.
Pull Request: https://projects.blender.org/blender/blender/pulls/121637
To know if link is connected to dangling reroute and can be skipped
as value-less, we need to know if reroute is dangling. This requires
graph traversal. Currently this is done by non-recursive iteration.
But this can lead quadratic complexity for some of the cases.
Other way is to make this linear while cache building.
Pull Request: https://projects.blender.org/blender/blender/pulls/120375
For historical reasons, the `multi_input_socket_index` was actually reversed
(large index comes first). This patch renames it to `multi_input_sort_id` and
adds a comment. This new name makes it less confusing that the id is reversed.
Pull Request: https://projects.blender.org/blender/blender/pulls/119652
Internal link is not created for a node when it has rotation output
socket. This is because the missing case for `sock_rotation` in
`get_internal_link_type_priority()` which fails to find input_socket
priority in this case.
Pull Request: https://projects.blender.org/blender/blender/pulls/118735
The depsgraph CoW mechanism is a bit of a misnomer. It creates an
evaluated copy for data-blocks regardless of whether the copy will
actually be written to. The point is to have physical separation between
original and evaluated data. This is in contrast to the commonly used
performance improvement of keeping a user count and copying data
implicitly when it needs to be changed. In Blender code we call this
"implicit sharing" instead. Importantly, the dependency graph has no
idea about the _actual_ CoW behavior in Blender.
Renaming this functionality in the despgraph removes some of the
confusion that comes up when talking about this, and will hopefully
make the depsgraph less confusing to understand initially too. Wording
like "the evaluated copy" (as opposed to the original data-block) has
also become common anyway.
Pull Request: https://projects.blender.org/blender/blender/pulls/118338
There is extra one user of shared enum definition in case this is new one
so already exist user is enough. Also using of `new` operator to construct
enum definition make this impossible to catch such leask for trivial type.
`Vector` have 4-element inline buffer so this was trivial case for <=4 items.
Pull Request: https://projects.blender.org/blender/blender/pulls/117599
This patch adds support for _Menu Switch_ nodes and enum definitions in
node trees more generally. The design is based on the outcome of the
[2022 Nodes Workshop](https://code.blender.org/2022/11/geometry-nodes-workshop-2022/#menu-switch).
The _Menu Switch_ node is an advanced version of the _Switch_ node which
has a customizable **menu input socket** instead of a simple boolean.
The _items_ of this menu are owned by the node itself. Each item has a
name and description and unique identifier that is used internally. A
menu _socket_ represents a concrete value out of the list of items.
To enable selection of an enum value for unconnected sockets the menu is
presented as a dropdown list like built-in enums. When the socket is
connected a shared pointer to the enum definition is propagated along
links and stored in socket default values. This allows node groups to
expose a menu from an internal menu switch as a parameter. The enum
definition is a runtime copy of the enum items in DNA that allows
sharing.
A menu socket can have multiple connections, which can lead to
ambiguity. If two or more different menu source nodes are connected to a
socket it gets marked as _undefined_. Any connection to an undefined
menu socket is invalid as a hint to users that there is a problem. A
warning/error is also shown on nodes with undefined menu sockets.
At runtime the value of a menu socket is the simple integer identifier.
This can also be a field in geometry nodes. The identifier is unique
within each enum definition, and it is persistent even when items are
added, removed, or changed. Changing the name of an item does not affect
the internal identifier, so users can rename enum items without breaking
existing input values. This also persists if, for example, a linked node
group is temporarily unavailable.
Pull Request: https://projects.blender.org/blender/blender/pulls/113445
The term `PIL` stands for "platform independent library." It exists since the `Initial Revision`
commit from 2002. Nowadays, we generally just use the `BLI` (blenlib) prefix for such code
and the `PIL` prefix feels more confusing then useful. Therefore, this patch renames the
`PIL` to `BLI`.
Pull Request: https://projects.blender.org/blender/blender/pulls/117325
This adds a new `Bake` node which allows saving and loading intermediate geometries.
Typical use cases we want address with this currently are:
* Bake some data for use with a render engine.
* Bake parts of the node tree explicitly for better performance.
For now, the format that is written to disk is not considered to be an import/export format.
It's not guaranteed that data written with one Blender version can be read by another
Blender version. For that it's better to use proper interchange formats. Better support for
those will be added eventually as well. We also plan an `Import Bake` node that allows
reading the blender-specific baked data independent of the Bake node and at different frames.
The baking works very similar to the baking in the simulation zone (UI and implementation
wise). Major differences are:
* The Bake node has a `Bake Still` and `Bake Animation` mode.
* The Bake node doesn't do automatic caching.
Implementation details:
* Refactored how we create the Python operators for moving socket items so that it also
makes sense for non-zones.
* The `ModifierCache` stores an independent map of `SimulationNodeCache` and
`BakeNodeCache`, but both share a common data structure for the actually baked data.
* For baking, the `Bake` node is added as a side-effect-node in the modifier. This will make
sure that the node is baked even if it's currently not connected to the output.
* Had to add a new `DEG_id_tag_update_for_side_effect_request` function that is used
during baking. It's necessary because I want to evaluate the object again even though none
of its inputs changed. The reevaluation is necessary to create the baked data. Using
`DEG_id_tag_update` technically works as well, but has the problem that it also uses the
`DEG_UPDATE_SOURCE_USER_EDIT` flag which (rightly) invalidates simulation caches
which shouldn't happen here.
* Slightly refactored the timeline drawing so that it can also show the baked ranges of
Bake nodes. It does not show anything for baked nodes with a in Still mode though.
* The bake operator is refactored to bake a list of `NodeBakeRequest` which makes the
code easier to follow compared to the previous nested
`ObjectBakeData > ModifierBakeData > NodeBakeData` data structure.
* The bake operators are disabled when the .blend file is not yet saved. This is technically
only necessary when the bake path depends on the .blend file path but seems ok to force
the user anyway (otherwise the bake path may be lost as well if it's set explicitly).
* The same operators are used to bake and delete single bakes in `Bake` nodes and
`Simulation Zones`. On top of that, there are separate operators of baking and deleting all
simulation bakes (those ignore bake nodes).
* The `Bake` node remembers which inputs have been fields and thus may be baked as attributes.
For that it uses an `Is Attribute` flag on the socket item. This is needed because the baked data
may still contain attribute data, even if the inputs to the bake node are disconnected.
* Similar to simulation zones, the behavior of `Bake` nodes is passed into the geometry nodes
evaluation from the outside (from the modifier only currently). This is done by providing the
new `GeoNodesBakeParams` in `GeoNodesCallData` when executing geometry nodes.
Next Steps (mostly because they also involve simulations):
* Visualize nodes that have not been evaluated in the last evaluation.
* Fix issue with seemingly loosing baked data after undo.
* Improve error handling when baked data is not found.
* Show bake node in link drag search.
* Higher level tools for managing bakes.
Pull Request: https://projects.blender.org/blender/blender/pulls/115466
NDEBUG is part of the C standard and disables asserts. Only this will
now be used to decide if asserts are enabled.
DEBUG was a Blender specific define, that has now been removed.
_DEBUG is a Visual Studio define for builds in Debug configuration.
Blender defines this for all platforms. This is still used in a few
places in the draw code, and in external libraries Bullet and Mantaflow.
Pull Request: https://projects.blender.org/blender/blender/pulls/115774
This helps solving the problem encountered in #113553. The problem is that we
currently can't support link-drag-search for nodes which have a dynamic declaration.
With this patch, there is only a single `declare` function per node type, instead of
the separate `declare` and `declare_dynamic` functions. The new `declare` function
has access to the node and tree. However, both are allowed to be null. The final
node declaration has a flag for whether it depends on the node context or not.
Nodes that previously had a dynamic declaration should now create as much of
the declaration as possible that does not depend on the node. This allows code
like for link-drag-search to take those sockets into account even if the other
sockets are dynamic.
For node declarations that have dynamic types (e.g. Switch node), we can also
add extra information to the static node declaration, like the identifier of the socket
with the dynamic type. This is not part of this patch though.
I can think of two main alternatives to the approach implemented here:
* Define two separate functions for dynamic nodes. One that creates the "static
declaration" without node context, and on that creates the actual declaration with
node context.
* Have a single declare function that generates "build instructions" for the actual
node declaration. So instead of building the final declaration directly, one can for
example add a socket whose type depends on a specific rna path in the node.
The actual node declaration is then automatically generated based on the build
instructions. This becomes quite a bit more tricky with dynamic amounts of sockets
and introduces another indirection between declarations and what sockets the node
actually has.
I found the approach implemented in this patch to lead to the least amount of
boilerplate (doesn't require a seperate "build instructions" data structure) and code
duplication (socket properties are still only defined in one place). At the same time,
it offers more flexibility to how nodes can be dynamic.
Pull Request: https://projects.blender.org/blender/blender/pulls/113742
Currently nodes are reordered so that the "on top" nodes are last in
the list. Node order changing for simple operations like selection
means we either have to reevaluate the node tree data-block on
selections or accept that the evaluated order can be different from the
original. Currently we do the latter (see d76a0e98ba), but
makes it complex to access nodes by index, and is hard to reason about.
Instead of reordering nodes, store the ui order in the node itself
and sort the nodes before drawing them or doing any processing
that depends on the "depth."
The "selected_nodes" list in the context is no longer ordered by the
recent selection.
Pull Request: https://projects.blender.org/blender/blender/pulls/113419
The goal is to reduce redundancy by abstracting over the different types of node
tree zones. This makes it easier to add new zone types and makes the intend of
code more clear. For example, now it is more obvious what code deals with zones
in general and what does simulation specific things.
Pull Request: https://projects.blender.org/blender/blender/pulls/112531
Calling an API function after the node panels patch does not internally
tag the node tree with `NTREE_CHANGED_INTERFACE` any more, because the
node tree is not directly accessible from `bNodeTreeInterface`. Before
node panels the API functions for interfaces could tag the tree directly
for later update consideration, which now requires explicit tagging
calls.
The fix is to add a flag and mutex directly to `bNodeTreeInterface`, so
API methods can tag after updates. This mostly copies runtime data
concepts from `bNodeTree`. The `ensure_interface_cache` method is
equivalent to `ensure_topology_cache` and should be called before
accessing `interface_inputs` and similar cache data.
Pull Request: https://projects.blender.org/blender/blender/pulls/111741
Listing the "Blender Foundation" as copyright holder implied the Blender
Foundation holds copyright to files which may include work from many
developers.
While keeping copyright on headers makes sense for isolated libraries,
Blender's own code may be refactored or moved between files in a way
that makes the per file copyright holders less meaningful.
Copyright references to the "Blender Foundation" have been replaced with
"Blender Authors", with the exception of `./extern/` since these this
contains libraries which are more isolated, any changed to license
headers there can be handled on a case-by-case basis.
Some directories in `./intern/` have also been excluded:
- `./intern/cycles/` it's own `AUTHORS` file is planned.
- `./intern/opensubdiv/`.
An "AUTHORS" file has been added, using the chromium projects authors
file as a template.
Design task: #110784
Ref !110783.
First implementation of node previews in the shader node editor. Using
the same user interface as compositor node previews, most shader nodes
can now be previewed (except group in/output and material output).
This is currently still an experimental feature, as polishing of the
user experience and performance improvements are planned. These will
be easier to do as incremental changes on this implementation.
See #110353 for details on the work that remains to be done and known
limitations.
Implementation notes:
We take advantage of the `RenderResult` available as `ImBuf` images to
store a `Render` for every viewed nested node tree present in a
`SpaceNode`. The computation is initiated at the moment of drawing nodes
overlays.
One render is started for the current nodetree, having a `ViewLayer`
associated with each previewed node. We separate the previewed nodes in
two categories: the shader ones and the non-shader ones.
- For non-shader nodes, we use AOVs which highly speed up the rendering
process by rendering every non-shader nodes at the same time. They are
rendered in the first `ViewLayer`.
- For shader nodes, we render them each in a different `ViewLayer`, by
rerouting the node to the output of the material in the preview scene.
The preview scene takes the same aspect as the Material preview scene,
and the same preview object is used.
At the moment of drawing the node overlay, we take the `Render` of the
viewed node tree and extract the `ImBuf` of the wanted viewlayer/pass
for each previewed node.
Pull Request: https://projects.blender.org/blender/blender/pulls/110065
Show node group inputs in the redo panel, including the
"use attribute" toggle. There are a few limitations that will
be solved separately:
- The redo panel is _always_ drawn, there is no way to show it conditionally yet
- There is no way to add the operator name to the redo panel title yet
- Attribute search is still missing for attribute inputs
Pull Request: https://projects.blender.org/blender/blender/pulls/109975
This adds support for running a set of nodes repeatedly. The number
of iterations can be controlled dynamically as an input of the repeat
zone. The repeat zone can be added in via the search or from the
Add > Utilities menu.
The main use case is to replace long repetitive node chains with a more
flexible alternative. Technically, repeat zones can also be used for
many other use cases. However, due to their serial nature, performance
is very sub-optimal when they are used to solve problems that could
be processed in parallel. Better solutions for such use cases will
be worked on separately.
Repeat zones are similar to simulation zones. The major difference is
that they have no concept of time and are always evaluated entirely in
the current frame, while in simulations only a single iteration is
evaluated per frame.
Stopping the repetition early using a dynamic condition is not yet
supported. "Break" functionality can be implemented manually using
Switch nodes in the loop for now. It's likely that this functionality
will be built into the repeat zone in the future.
For now, things are kept more simple.
Remaining Todos after this first version:
* Improve socket inspection and viewer node support. Currently, only
the first iteration is taken into account for socket inspection
and the viewer.
* Make loop evaluation more lazy. Currently, the evaluation is eager,
meaning that it evaluates some nodes even though their output may not
be required.
Pull Request: https://projects.blender.org/blender/blender/pulls/109164
