Logics of nodes breaks under certain circumstances #93269

New Issue

Andrey · 2021-11-21T18:22:12+01:00

Andrey commented

2021-11-21 18:22:12 +01:00

System Information
Operating system: Windows 10
Graphics card: GTX 1060 6GB

Blender Version
Broken: 2.83LTS - 3.1.0 alpha (tested only in those versions, so it doesn't means that it doesn't appears in version before 2.83)

Short description of error
Nodes become unpredictable, and logic brokes once user does some unusual actions.

Exact steps for others to reproduce the error

Open shader editor, add Vector Math node.
Connect output of Vector Math node to any other input, for example to the Math node input. (Mode of Vector Math node by default is "Add", and "Add" is returns a vector)
Change mode of Vector Math node to Length, Distance, or Dot Product. (Those 3 modes return Value Instead of Vector)
Now you see what i mean.

My thoughts about whats happening here
As you might notice, this happens when existing connection changes its return type from one type to another, example on above shows "Vector To Value" change, but same will happen when you'll try "Value To Vector".
So my hypothesis is that blender doesn't expects that connections between nodes might change from one type to another. So if this hypothesis is correct, then it means that it might happen not only with Vector Math node, but any other node that can have its output type to be changed.

What i mean by "logics of nodes brokes"?

Visual connection between nodes disappear, but they still connected in some sense, for example Math node still shows that something is connected to one of its inputs, so user can't change value.
1.2. You might try to use Ctrl + RMB shortcut to cut connection between nodes, but blender can't register any connection.
1.3. You can manually detach output of Vector Math node from the input of Math node, and you will success, however, if before doing so, you will move Vector Math node to other
place, and then perform note 1.3, you can see that blender didn't updated position of Vector Math node.

(Since screenshot doesn't capture cursor, to help you undestand what happens on the screen, there is cursor drawn by hand)
Computation of nodes brokes. Example:
Simple node setup, 2 node groups that use same 3 nodes, difference between those groups is that group on top builded with Vector Math node at first setted to "Add" mode, then when building node group setup is done, Vector Math node mode changed to "Distance", causing bug to appear.
Node group on bottom was initially builded with Vector Math node mode setted to "Distance".
Output of top node group

Output of bottom node group

At first i was expecting both node groups to perform exactly the same, but as you can see it doesn't.

Interesting finding
I noticed if i disconnect Vector Math node from Math node in bottom node group, and manually set value to 0 in Math node, it seems to perform same as broken top node group.

Last thing that you need to know and try:

Open shader editor, add Vector Math and Math nodes.
Connect output of Vector Math node to first input of Math node.
Change mode of Vector Math node to Length, Distance, or Dot Product.
Connect output of Vector Math node to second input of Math node.
Using Ctrl + MMB shortcut scroll through different modes of Vector Math node.
Hard to explain result with words, just try and see it.

**System Information** Operating system: Windows 10 Graphics card: GTX 1060 6GB **Blender Version** Broken: 2.83LTS - 3.1.0 alpha (tested only in those versions, so it doesn't means that it doesn't appears in version before 2.83) **Short description of error** Nodes become unpredictable, and logic brokes once user does some unusual actions. **Exact steps for others to reproduce the error** 1. Open shader editor, add Vector Math node. 2. Connect output of Vector Math node to any other input, for example to the Math node input. (Mode of Vector Math node by default is "Add", and "Add" is returns a vector) 3. Change mode of Vector Math node to Length, Distance, or Dot Product. (Those 3 modes return Value Instead of Vector) 4. Now you see what i mean. ![00001.jpg](https://archive.blender.org/developer/F11837939/00001.jpg) **My thoughts about whats happening here** As you might notice, this happens when existing connection changes its return type from one type to another, example on above shows "Vector To Value" change, but same will happen when you'll try "Value To Vector". So my hypothesis is that blender doesn't expects that connections between nodes might change from one type to another. So if this hypothesis is correct, then it means that it might happen not only with Vector Math node, but any other node that can have its output type to be changed. **What i mean by "logics of nodes brokes"?** 1. Visual connection between nodes disappear, but they still connected in some sense, for example Math node still shows that something is connected to one of its inputs, so user can't change value. 1.2. You might try to use Ctrl + RMB shortcut to cut connection between nodes, but blender can't register any connection. 1.3. You can manually detach output of Vector Math node from the input of Math node, and you will success, however, if before doing so, you will move Vector Math node to other place, and then perform note 1.3, you can see that blender didn't updated position of Vector Math node. ![00002.jpg](https://archive.blender.org/developer/F11838028/00002.jpg) (Since screenshot doesn't capture cursor, to help you undestand what happens on the screen, there is cursor drawn by hand) 2. Computation of nodes brokes. Example: Simple node setup, 2 node groups that use same 3 nodes, difference between those groups is that group on top builded with Vector Math node at first setted to "Add" mode, then when building node group setup is done, Vector Math node mode changed to "Distance", causing bug to appear. Node group on bottom was initially builded with Vector Math node mode setted to "Distance". **Output of top node group** ![0101.jpg](https://archive.blender.org/developer/F11838083/0101.jpg) **Output of bottom node group** ![0102.jpg](https://archive.blender.org/developer/F11838145/0102.jpg) At first i was expecting both node groups to perform exactly the same, but as you can see it doesn't. **Interesting finding** I noticed if i disconnect Vector Math node from Math node in bottom node group, and manually set value to 0 in Math node, it seems to perform same as broken top node group. ![0103.jpg](https://archive.blender.org/developer/F11838174/0103.jpg) **Last thing that you need to know and try:** 1. Open shader editor, add Vector Math and Math nodes. 2. Connect output of Vector Math node to first input of Math node. 3. Change mode of Vector Math node to Length, Distance, or Dot Product. 4. Connect output of Vector Math node to second input of Math node. 5. Using Ctrl + MMB shortcut scroll through different modes of Vector Math node. Hard to explain result with words, just try and see it.

Andrey commented

2021-11-21 18:22:12 +01:00

Added subscriber: @DEBIHOOD

Andrey commented

2021-11-21 19:32:46 +01:00

Oops! Seems like this is duplicate of #83269
But i think this task that i created containts a bit more information.
Also #83269 seems to be abandoned.
So I'll just leave it as it is, cause i have no idea about what to do with it in this situation, and someone with more knowledge will decide what to do with it next.

Oops! Seems like this is duplicate of #83269 But i think this task that i created containts a bit more information. Also #83269 seems to be abandoned. So I'll just leave it as it is, cause i have no idea about what to do with it in this situation, and someone with more knowledge will decide what to do with it next.

Richard Antalik commented

2021-11-24 10:15:55 +01:00

Added subscriber: @iss

Richard Antalik commented

2021-11-24 10:15:55 +01:00

Thanks for finding duplicate, I am pretty sure I saw this discussed, so developers know about this issue, but I assume that no solution has been found. Tasks can't really be abandoned, only resolved.

Richard Antalik commented

2021-11-24 10:16:11 +01:00

Closed as duplicate of #83269

Richard Antalik closed this issue

2021-11-24 10:16:11 +01:00

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Logics of nodes breaks under certain circumstances #93269