Multiple output nodes in a group produce "undefined behaviour" #70506

New Issue

Matthew Wiebe · 2019-10-04T06:03:57+02:00

Matthew Wiebe commented

2019-10-04 06:03:57 +02:00

Linux
GTX 1050

v2.81 Alpha
Hash: fbc096cf07

I'm not sure what the expected behaviour is here, in other node-based software like Native Instruments Reaktor you have separate nodes for each input and output socket in a "group", which reduces the amount of lines converging and diverging in one place. I'm not sure if blender is supposed to have this, and as such I'm not sure if what I'm seeing is a feature half-implemented or an unintended behaviour to be removed.

Description of Problem:
When a group has multiple output nodes inside of it, only the active node sends output, even if there are no conflicts (each socket is only connected on one output node)
This occurs in both Eevee and Cycles.
Even worse, in the Compositor, output sockets which are not fed a connection in the selected output node seem to break the next node in the graph outside. (I assume they are producing NaNs)
Multiple input nodes work just fine though, the signal is duplicated as expected and you can hide the sockets you're not using and basically use a separate node per socket if you want.

Node Group Bug.blend

In the attached blend file there is a viewport & shader editor with a group to demonstrate how this bug breaks shaders.
There is also an imageviewer window and compositor to demonstrate how this bug breaks the compositor. (obviously press F12 to refresh the compositor inputs)

open the attached blend
set the viewport to rendered (either cycles or eevee) and press F12
click on the group output nodes to see the different ways they break the node graphs that contain them

(it is my personal hope that whoever fixes this bug does so by deciding on a useful behaviour for multiple output nodes and not by simply removing them. they could improve organization by allowing you to output from different places in the group graph)

Linux GTX 1050 v2.81 Alpha Hash: fbc096cf075b I'm not sure what the expected behaviour is here, in other node-based software like Native Instruments Reaktor you have separate nodes for each input and output socket in a "group", which reduces the amount of lines converging and diverging in one place. I'm not sure if blender is supposed to have this, and as such I'm not sure if what I'm seeing is a feature half-implemented or an unintended behaviour to be removed. Description of Problem: When a group has multiple output nodes inside of it, only the active node sends output, even if there are no conflicts (each socket is only connected on one output node) This occurs in both Eevee and Cycles. Even worse, in the Compositor, output sockets which are not fed a connection in the selected output node seem to break the next node in the graph outside. (I assume they are producing NaNs) Multiple input nodes work just fine though, the signal is duplicated as expected and you can hide the sockets you're not using and basically use a separate node per socket if you want. [Node Group Bug.blend](https://archive.blender.org/developer/F7788713/Node_Group_Bug.blend) In the attached blend file there is a viewport & shader editor with a group to demonstrate how this bug breaks shaders. There is also an imageviewer window and compositor to demonstrate how this bug breaks the compositor. (obviously press F12 to refresh the compositor inputs) open the attached blend set the viewport to rendered (either cycles or eevee) and press F12 click on the group output nodes to see the different ways they break the node graphs that contain them (it is my personal hope that whoever fixes this bug does so by deciding on a useful behaviour for multiple output nodes and not by simply removing them. they could improve organization by allowing you to output from different places in the group graph)

Matthew Wiebe commented

2019-10-04 06:03:57 +02:00

Added subscriber: @cerebral

Germano Cavalcante commented

2019-10-04 20:37:00 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2019-10-04 20:37:00 +02:00

Changed status from 'Open' to: 'Archived'

Germano Cavalcante closed this issue

2019-10-04 20:37:00 +02:00

Germano Cavalcante self-assigned this 2019-10-04 20:37:00 +02:00

Germano Cavalcante commented

2019-10-04 20:37:00 +02:00

The manual is not very clear, but apparently only the first Output Node works.
https://docs.blender.org/manual/en/latest/editors/texture_node/types/groups.html#make-group

So this is a known situation, not a bug.

The manual is not very clear, but apparently only the first Output Node works. https://docs.blender.org/manual/en/latest/editors/texture_node/types/groups.html#make-group So this is a known situation, not a bug.

Matthew Wiebe commented

2019-10-04 23:22:05 +02:00

What? so you're saying the interface lets us create nodes that don't work properly but that isn't a bug? i'm kind of baffled by this

Germano Cavalcante removed their assignment 2019-10-05 16:42:49 +02:00

Brecht Van Lommel was assigned by Germano Cavalcante

2019-10-05 16:42:49 +02:00

Germano Cavalcante commented

2019-10-05 16:42:49 +02:00

Added subscriber: @brecht

Germano Cavalcante commented

2019-10-05 16:42:49 +02:00

@brecht, do you have any comments about this?
Indeed, as @cerebral pointed, keeping useless nodes is kind of curious.

@brecht, do you have any comments about this? Indeed, as @cerebral pointed, keeping useless nodes is kind of curious.

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Multiple output nodes in a group produce "undefined behaviour" #70506