Not possible to link a "Vector math" node using operation "Dot product" to another node in python . #72901

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Cédric · 2020-01-04T17:50:14+01:00

Cédric commented

2020-01-04 17:50:14 +01:00

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.66

Blender Version
Broken: version: 2.81 official
Broken: version: 2.82 (sub 6), branch: master, commit date: 2020-01-03 10:02, hash: 9b74e648c5

Short description of error
When using the Vector Math node with the "Dot product" operation, it is not possible to link this node to another one. The link is invisible and broken.

Exact steps for others to reproduce the error
Using the factory settings, select the cube and copy/paste and execute the following script, wich create 2 nodes and try to connect them or open the dot_product.blend wich includ the script :

import bpy

mat = bpy.data.materials['Material']

# Clear node tree
mat.node_tree.nodes.clear()

dot_product = mat.node_tree.nodes.new('ShaderNodeVectorMath')
dot_product.operation = 'DOT_PRODUCT'
dot_product.location = (-580.0, 80.0)

subtract = mat.node_tree.nodes.new('ShaderNodeMath')
subtract.operation = 'SUBTRACT'
subtract.location = (-360.0, 40.0)

mat.node_tree.links.new(dot_product.outputs[0], subtract.inputs[0])

dot_product.blend

As you can see, the nodes are not connected together and it is not possible to cut the link. Changing the vector math to a vector operation works :

**System Information** Operating system: Windows-10-10.0.17763-SP0 64 Bits Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.66 **Blender Version** Broken: version: 2.81 official Broken: version: 2.82 (sub 6), branch: master, commit date: 2020-01-03 10:02, hash: `9b74e648c5` **Short description of error** When using the Vector Math node with the "Dot product" operation, it is not possible to link this node to another one. The link is invisible and broken. **Exact steps for others to reproduce the error** Using the factory settings, select the cube and copy/paste and execute the following script, wich create 2 nodes and try to connect them or open the dot_product.blend wich includ the script : ``` import bpy mat = bpy.data.materials['Material'] # Clear node tree mat.node_tree.nodes.clear() dot_product = mat.node_tree.nodes.new('ShaderNodeVectorMath') dot_product.operation = 'DOT_PRODUCT' dot_product.location = (-580.0, 80.0) subtract = mat.node_tree.nodes.new('ShaderNodeMath') subtract.operation = 'SUBTRACT' subtract.location = (-360.0, 40.0) mat.node_tree.links.new(dot_product.outputs[0], subtract.inputs[0]) ``` [dot_product.blend](https://archive.blender.org/developer/F8259821/dot_product.blend) As you can see, the nodes are not connected together and it is not possible to cut the link. Changing the vector math to a vector operation works : ![2020-01-04_17-29-08.gif](https://archive.blender.org/developer/F8259819/2020-01-04_17-29-08.gif)

Cédric commented

2020-01-04 17:50:14 +01:00

Added subscriber: @Clarkx

Stanislav Blinov commented

2020-01-04 18:20:28 +01:00

Added subscriber: @Stan_Pancakes

Stanislav Blinov commented

2020-01-04 18:20:28 +01:00

It would seem that to work correctly, this should be
mat.node_tree.links.new(dot_product.outputs- [x], subtract.inputs[0])
(first output is vector, second is scalar, but only one of them is displayed depending on operation).

The same behavior can be recreated without a script: add the same two nodes (Vector Math and Math), connect the vector output of Vector Math to the value input of Math, then switch Vector Math to 'Dot Product'. Value input of Math node will remain "connected", even though no noodle is displayed.

It would seem that to work correctly, this should be ```mat.node_tree.links.new(dot_product.outputs- [x], subtract.inputs[0])``` (first output is vector, second is scalar, but only one of them is displayed depending on operation). The same behavior can be recreated without a script: add the same two nodes (Vector Math and Math), connect the vector output of Vector Math to the value input of Math, then switch Vector Math to 'Dot Product'. Value input of Math node will remain "connected", even though no noodle is displayed.

Robert Guetzkow commented

2020-01-04 18:27:26 +01:00

Added subscriber: @rjg

Robert Guetzkow commented

2020-01-04 18:27:26 +01:00

The issue is that the Vector Math node has actually two output sockets, one of type [bpy.types.NodeSocketVector ]] and one of type https:*docs.blender.org/api/current/bpy.types.NodeSocketFloat.html . Since you want to connect the Vector Math node to the Math node that only has input sockets of type [ https://docs.blender.org/api/current/bpy.types.NodeSocketFloat.html | bpy.types.NodeSocketFloat , you will have to use the latter.

In order to let Blender determine the appropriate socket based on its type you can address them by name instead of index:

mat.node_tree.links.new(subtract.inputs["Value"], dot_product.outputs["Value"])

If you want to use indices, you will have to use the one of appropriate type:

mat.node_tree.links.new(subtract.inputs[0], dot_product.outputs[1])

The issue is that the *Vector Math* node has actually two output sockets, one of type [bpy.types.NodeSocketVector ]] and one of type [[ https:*docs.blender.org/api/current/bpy.types.NodeSocketFloat.html | bpy.types.NodeSocketFloat ]]. Since you want to connect the *Vector Math* node to the *Math* node that only has input sockets of type [[ https://docs.blender.org/api/current/bpy.types.NodeSocketFloat.html | bpy.types.NodeSocketFloat ](https:*docs.blender.org/api/current/bpy.types.NodeSocketVector.html), you will have to use the latter. In order to let Blender determine the appropriate socket based on its type you can address them by name instead of index: ``` mat.node_tree.links.new(subtract.inputs["Value"], dot_product.outputs["Value"]) ``` If you want to use indices, you will have to use the one of appropriate type: ``` mat.node_tree.links.new(subtract.inputs[0], dot_product.outputs[1]) ```

Robert Guetzkow commented

2020-01-04 18:39:08 +01:00

Changed status from 'Needs Triage' to: 'Archived'

Robert Guetzkow closed this issue

2020-01-04 18:39:08 +01:00

Robert Guetzkow self-assigned this 2020-01-04 18:39:08 +01:00

Robert Guetzkow commented

2020-01-04 18:39:08 +01:00

This is working as designed and is therefore not a bug.

Cédric commented

2020-01-04 18:52:30 +01:00

Thanks to both of you for the tips, it's working now using your advise. Sorry for the misunderstanding !
But as @Stan_Pancakes say, the same behavior appear when changing manually the operation in the node editor, wich is really strange

Thanks to both of you for the tips, it's working now using your advise. Sorry for the misunderstanding ! But as @Stan_Pancakes say, the same behavior appear when changing manually the operation in the node editor, wich is really strange

Robert Guetzkow commented

2020-01-04 19:51:44 +01:00

@Clarkx Basically one output socket and its connections are hidden when changing to an operation that produces a different type of output and therefore requires a different output socket. Internally the connection is still remembered.

Cédric commented

2020-01-04 20:17:36 +01:00

@rjg Yes I understand now, but as user it's really disconcerting to see the link disappearing without any warning when you change from a vector to a float, but the connection is still there. And as an addon developper, there is no error telling you that the link is not corresponding to the operation. But, well, it's working now, not a big deal. Again, thanks a lot for taking the time.

Stanislav Blinov commented

2020-01-04 20:18:33 +01:00

@rjg Is this documented somewhere? I can't find anything on this in the manual, but may be looking in the wrong place. What use is there for current behavior? Confusing UI should have a reason (connected socket with no visible connection).

Robert Guetzkow commented

2020-01-04 23:53:57 +01:00

@Clarkx @Stan_Pancakes I agree that this behavior should be documented. Currently the manual states that the chosen operator determines the output data type, but it doesn't explain how existing links are handled when switching between them.

The output of the node is dynamic. It is either a vector or a scalar depending on the operator. For instance, the Length operator have a scalar output while the Add operator have a vector output.

Since I wasn't involved in the design or implementation of this feature, I can't say why the decision was made not to clear existing links when switching the operation. I'm sure there are good arguments for both approaches.

@Clarkx @Stan_Pancakes I agree that this behavior should be documented. Currently the [manual ](https://docs.blender.org/manual/en/latest/render/shader_nodes/converter/vector_math.html#outputs) states that the chosen operator determines the output data type, but it doesn't explain how existing links are handled when switching between them. > The output of the node is dynamic. It is either a vector or a scalar depending on the operator. For instance, the Length operator have a scalar output while the Add operator have a vector output. Since I wasn't involved in the design or implementation of this feature, I can't say why the decision was made not to clear existing links when switching the operation. I'm sure there are good arguments for both approaches.

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Not possible to link a "Vector math" node using operation "Dot product" to another node in python . #72901