Geometry Nodes: new repeat zone #109164
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Lukas Tönne
Hans Goudey
Dalai Felinto
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Reference: blender/blender#109164
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Delete Branch "JacquesLucke/blender:serial-loop"
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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 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:
@blender-bot package
Package build started. Download here when ready.
@blender-bot package
Package build started. Download here when ready.
WIP: Geometry Nodes: add support for serial loopsto Geometry Nodes: add support for serial loopsAt the moment if I mouse over the Menu entry for Serial Loop Zone it says "undocumented operator".
Also I'm not sure which category this should go to. In the future once we get Parallel Loop as well, would it also go to Layout?
Why not replace the Simulation category with an Scopes category? (Simulation scopes, Serial Loops scopes, Parallel Loop scopes, ...).
Yes, that's a good question. I don't really have a great answer yet. Right now I'd say yes.
We call them zones, not scopes. Having a zones category is a possibility, but currently I'm not convinced that this is the way to go as they will all be kind of independent.
Having Simulation on its own category also makes it easier for assets to get added there. So not sure I would combine them both. I would combine the loops, not sure if on its own category or what.
I ran out of time before I got to
geometry_nodes_lazy_function.cc, so I didn't read the interesting part yet. Just a couple small comments so far.@ -348,0 +384,4 @@node = self.get_output_node(context)loop_items = node.loop_items# Remember index to move the item.This should copy the active type when possible. See
0f36f44db8@ -81,0 +86,4 @@int iteration_;public:SerialLoopZoneComputeContext(const ComputeContext *parent, int output_node_id, int iteration);int->int32_t@ -101,1 +101,4 @@}if (ELEM(node.type, GEO_NODE_SERIAL_LOOP_INPUT, GEO_NODE_SERIAL_LOOP_OUTPUT)) {aal::RelationsInNode &relations = scope.construct<aal::RelationsInNode>();/* Add all possible relations for now. The inferencing algorithm has to be updated to detect aFeels more natural to me to write this as a "TODO" comment like
TODO: Add a smaller set of relations. For now, adding all possible relations is correct.@ -0,0 +47,4 @@if (!output_node) {return true;}NodeGeometrySerialLoopOutput &storage = *static_cast<NodeGeometrySerialLoopOutput *>(I'd go with
autohere, keeps it on one line@ -1424,0 +1435,4 @@IndexRange main_output_usages;IndexRange border_link_usages;Map<int, int> attribute_set_input_by_field_source_index;Could use some comments IMO, this name is pretty tricky to parse
@ -1424,0 +1582,4 @@Array<lf::ValueUsage> output_usages(body_outputs_num, lf::ValueUsage::Used);Array<bool> set_outputs(body_outputs_num, false);Array<bool> tmp_main_input_usages(loop_items_num);I think this would be easier to read if there were comments describing what each block of code did. Even if it's "obvious" when you read the code, it would help when skimming it. For example "Retrieve inputs from outside the loop" or something. "Destruct values that are not needed after the evaluation anymore" already does that here.
@blender-bot build
This generally looks good to me.
For the timing overlay in the node editor, I wonder if it makes more sense to show the sum of all the node's time for all loop iterations.
Found a crash:
This is a little greedy graph coloring implementation i'm trying out. We probably want a built-in node for this stuff, but it's sufficiently loopy to work as a test.
Graph coloring is a necessary step for efficient constraint solving with Gauss-Seidel methods. It allows separating constraints into groups, within which each constraint is independent of all others. This way the solver can be parallelized as much as possible.
Moving an item of the serial loop in the sidebar does not update the node sockets right away. After reloading the file the sockets get shuffled into the correct order.
Duplicating the serial loop output node crashes Blender atm. Duplicating the input node un-pairs it.
The simulation zone nodes are both copied when either one of them is copied, and they remain paired. Would be worth implementing this for serial loops too, and possibly share some code.
Loop-inside-loop seems to be slightly problematic: i implemented a bitonic sorting node group, which has an outer loop ("stage" from 0 to log2(n)) and an inner loop ("pass" descending from stage to 0). This works beautifully when it works, but about half the time the outer loop does not produce any Geometry.
Test file: sorting.blend
Sometimes (randomly) the geometry of the inner loop is not passed on to the outer loop. Tooltip says the inner loop Geometry output has all the points but the outer loop Geometry is empty. I could implement this with a single loop, but i assume nested loops should be working as well.
Are you sure that is implemented? Doesn't look like it.
Thanks for discovering this. Nice thing was, that triggered an assert in a debug build. Should be fixed now.
Hah, i should have checked. I thought i had implemented this but looks like that's not the case. Maybe was just an experiment in a branch. If the crash on copying outputs is fixed i guess that's good enough for now. Copying a single zone node is kinda useless right now because we don't yet have a "fix zone" operator, so maybe that could be added in future.
Works great and i didn't spot any more issues with the code.
I agree with Hans. The timings inside the loop are typically a factor of 1/N smaller than the timings outside, which makes it difficult to compare numbers and figure out which parts really are slow. Fast loops also fall into the "< 1ms" bracket so you don't get a whole lot of information. Ideally we'd also get some numbers about how often a particular node was executed, in case some branches are executed more frequently and skew the result. That can all happen later.
LGTM
FYI, I mainly waiting with merging this because we should have a more final sign off for the name "serial loop" (or discuss other alternatives).
As discussed today in the geometry-nodes daily meeting:
Name: Repeat (Zone)
Category: Utilities
Color: [0.181164, 0.082283, 0.028426, 0.200000]
Input/Output: The nodes will be "Repeat Input" and "Repeat Output"
Mockup of the color:
Rational:
Geometry Nodes: add support for serial loopsto Geometry Nodes: new repeat zone@blender-bot build
Note that due to the rename from
Serial Loop ZonetoRepeat Zone, files created with the experimental branch do not work out of the box anymore. I made it so that it doesn't crash when opening those files though. So one can manually replace the undefined nodes with a new Repeat Zone.@ -353,0 +378,4 @@class RepeatZoneItemAddOperator(RepeatZoneOperator, Operator):"""Add a repeat item to the repeat zone"""I'd go with "item" instead of "repeat item" which sounds a bit unnatural but it's not a big deal either way.
@blender-bot package
Package build started. Download here when ready.
It seems to be working as expected. I'm not crazy about the name
iterationsbut I think it is fine.@blender-bot build
Awesome. Is there any plan to add this to the compositor too?