Now impossible to make negative volumes :( #41495

New Issue

gandalf3 · 2014-08-19T22:34:31+02:00

gandalf3 commented

2014-08-19 22:34:31 +02:00

System Information
Archlinux
GTX 460

Blender Version
Broken: 2.71
Worked: 2.70

Short description of error
The intent of the fix to #39284 seems to have been to make it harder to accidentally make a potentially confusing light-emitting volume, which makes sense.
However, it now seems impossible to get such an effect. Using negative colors as suggested doesn't seem to work, as they are now clamped as well (77f815f67a). Using a negative value node also doesn't seem to work.

This is a cool effect, and IMO it's fine to allow negative/unusual values if they are explicitly typed in (as opposed to sliding with the mouse, where it's easy to do something accidentally).

In most places, Blender seems to go by the philosophy that the user knows what they are doing,
with well-placed exceptions for dangerous/non-reversible actions like opening a new file and losing changes to the current one, where it asks for confirmation.
Since setting a volume to be negative is easily reversible, IMO the user doesn't need as much "stupidity protection" :)

This is allowed with lamps, so I don't see the reason for disabling this on volumes.

Exact steps for others to reproduce the error

Open negative_volume.blend in 2.71, and compare to 2.70

**System Information** Archlinux GTX 460 **Blender Version** Broken: 2.71 Worked: 2.70 **Short description of error** The intent of the fix to #39284 seems to have been to make it harder to accidentally make a potentially confusing light-emitting volume, which makes sense. However, it now seems *impossible* to get such an effect. Using negative colors as suggested doesn't seem to work, as they are now clamped as well (77f815f67a). Using a negative value node also doesn't seem to work. This is a cool effect, and IMO it's fine to allow negative/unusual values if they are explicitly typed in (as opposed to sliding with the mouse, where it's easy to do something accidentally). In most places, Blender seems to go by the philosophy that the user knows what they are doing, with well-placed exceptions for dangerous/non-reversible actions like opening a new file and losing changes to the current one, where it asks for confirmation. Since setting a volume to be negative is easily reversible, IMO the user doesn't need as much "stupidity protection" :) This is allowed with lamps, so I don't see the reason for disabling this on volumes. **Exact steps for others to reproduce the error** 1. Open [negative_volume.blend](https://archive.blender.org/developer/F105130/negative_volume.blend) in 2.71, and compare to 2.70

gandalf3 commented

2014-08-19 22:34:31 +02:00

Changed status to: 'Open'

gandalf3 commented

2014-08-19 22:34:31 +02:00

Added subscriber: @gandalf3

Adam Friesen commented

2014-08-20 01:00:51 +02:00

Added subscriber: @Ace_Dragon

Adam Friesen commented

2014-08-20 01:00:51 +02:00

1). This isn't really a 'bug'.

2). If you use a value node hooked into a color mix node, you can still get negative color values.

3). I'm not so sure of 'stupidity protection' as it is to make sure that it's not so easy to get completely unintended, error-prone results by accident (which someone else might see as a bug). This way you have such results only present when the user intends it.

1). This isn't really a 'bug'. 2). If you use a value node hooked into a color mix node, you can still get negative color values. 3). I'm not so sure of 'stupidity protection' as it is to make sure that it's not so easy to get completely unintended, error-prone results by accident (which someone else might see as a bug). This way you have such results only present when the user intends it.

gandalf3 commented

2014-08-20 01:49:58 +02:00

@Ace_Dragon

It depends on whether you think of negative volumes as a feature or not. Negative lamps seem to be a feature, so why not negative volumes? If negative volumes are a feature, then as a missing feature, they could be classified as a bug. Anyway, if this is off-topic here, where should I ask? (the mailing list?)
Ah, thanks. That's a nice trick, but I still can't seem to use it to create a negative volume.. Am I missing something?
Well.. What you said is pretty much what I meant by "stupidity protection", but perhaps that was a rather strong choice of words..

What I mean is: It should be pretty hard to type a minus sign by accident, but if by some chance the user does, then it should be pretty easy to remove it. On the *extreme* outside chance that they don't know to remove it or notice it that it's there, then hopefully google can help them.. In other words, IMO only allowing negative numbers to be entered by typing should be enough.

This seems to be working fine for lamps, so why all the clamping on volumes?

@Ace_Dragon 1. It depends on whether you think of negative volumes as a feature or not. Negative lamps seem to be a feature, so why not negative volumes? If negative volumes are a feature, then as a missing feature, they could be classified as a bug. Anyway, if this is off-topic here, where should I ask? (the mailing list?) 2. Ah, thanks. That's a nice trick, but I still can't seem to use it to create a negative volume.. Am I missing something? 3. Well.. What you said is pretty much what I meant by "stupidity protection", but perhaps that was a rather strong choice of words.. ``` What I mean is: It should be pretty hard to type a minus sign by accident, but if by some chance the user does, then it should be pretty easy to remove it. On the *extreme* outside chance that they don't know to remove it or notice it that it's there, then hopefully google can help them.. In other words, IMO only allowing negative numbers to be entered by typing should be enough. ``` This seems to be working fine for lamps, so why all the clamping on volumes?

Thomas Dinges commented

2014-08-20 12:06:04 +02:00

Added subscriber: @ThomasDinges

Thomas Dinges commented

2014-08-22 03:30:15 +02:00

It should still be possible with OSL?

Thomas Dinges commented

2014-08-27 14:46:25 +02:00

Added subscriber: @Sergey

Thomas Dinges commented

2014-08-27 14:46:25 +02:00

Sergey, any strong opinion here?

Imho, the negative volume effect can be nice, but is too unpredictable to allow per default. If you want it, you can write a custom OSL shader which does not limit the color or density.

Sergey, any strong opinion here? Imho, the negative volume effect can be nice, but is too unpredictable to allow per default. If you want it, you can write a custom OSL shader which does not limit the color or density.

Campbell Barton commented

2014-08-27 14:48:19 +02:00

Added subscriber: @ideasman42

Campbell Barton commented

2014-08-27 14:48:19 +02:00

We can allow be explicitly setting limits so for some colors negative values are supported.

The reason I added this check is many colors could be set to negative values and really didn't do anything useful, or they gave some strange, accidental result.

So on a case-by-case basis this can be added back, but first check the math that deals with the color handles this correct.

We can allow be explicitly setting limits so for some colors negative values are supported. The reason I added this check is many colors could be set to negative values and really didn't do anything useful, or they gave some strange, accidental result. So on a case-by-case basis this can be added back, but first check the math that deals with the color handles this correct.

Sergey Sharybin was assigned by Bastien Montagne

2014-10-10 19:41:24 +02:00

Bastien Montagne commented

2014-10-10 19:41:24 +02:00

Added subscriber: @mont29

Brecht Van Lommel commented

2014-11-09 04:10:06 +01:00

Changed status from 'Open' to: 'Archived'

Brecht Van Lommel closed this issue

2014-11-09 04:10:06 +01:00

Brecht Van Lommel commented

2014-11-09 04:10:06 +01:00

Added subscriber: @brecht

Brecht Van Lommel commented

2014-11-09 04:10:06 +01:00

There's no reason to keep this bug open, the fix in #39284 intentionally disabled this "feature" which the volume integrator really can't handle correctly and will cause all kinds of bugs in multiple importance sampling, render passes and so on. Negative density is non-sensical and I don't believe any user actually knows what they are doing when using negative density. We can't keep around render bugs just because they look interesting.

Sign in to join this conversation.

No Label

Download

What's New

Blender Studio

Manual

Developers Blog

Documentation

Benchmark

Blender Conference

Development Fund

One-time Donations

Now impossible to make negative volumes :( #41495