POV-Ray : Newsgroups : povray.general : no_image ignored in nested (difference > union > object) CSG member Server Time
29 Mar 2024 04:09:03 EDT (-0400)
  no_image ignored in nested (difference > union > object) CSG member (Message 9 to 18 of 18)  
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From: Alain Martel
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 25 Mar 2020 14:04:08
Message: <5e7b9d18$1@news.povray.org>
Le 2020-03-25 à 13:11, William F Pokorny a écrit :

> -----------
> The interior{} and subsurface{}(1) object and finish modifier block 
> results, respectively, vary where definitions are part of components 
> making up any given csg.
> 
> 
> The disclaimer here is I've not created but a half dozen test cases to 
> verify behavior. With the no_* and hollow keywords confident without 
> testing. Anyway, I think I have the behaviors through csg mostly right...
> 
> Bill P.

In the case of subsurface, if the distance between two surface is 
similar or smaller than the translucency value, then, we start to see 
through the object. In a CSG, if the back surface don't have a similar 
translucency, you can expect some unexpected results.


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From: Jim Holsenback
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 27 Mar 2020 08:26:50
Message: <5e7df10a$1@news.povray.org>
On 3/25/20 1:11 PM, William F Pokorny wrote:
> On 3/25/20 8:05 AM, William F Pokorny wrote:
>> On 3/25/20 5:52 AM, Jim Holsenback wrote:
> ...
>>
>> Anyway, I've promised to do some other stuff first thing this morning. 
>> I'll come back to this thread later.

Thanks Bill and Alain for the input...
When you get a moment please review: 
http://wiki.povray.org/content?title=Special:RecentChanges&hidebots=0


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 27 Mar 2020 09:58:52
Message: <5e7e069c$1@news.povray.org>
On 3/27/20 8:26 AM, Jim Holsenback wrote:
> On 3/25/20 1:11 PM, William F Pokorny wrote:
>> On 3/25/20 8:05 AM, William F Pokorny wrote:
>>> On 3/25/20 5:52 AM, Jim Holsenback wrote:
>> ...
>>>
>>> Anyway, I've promised to do some other stuff first thing this 
>>> morning. I'll come back to this thread later.
> 
> Thanks Bill and Alain for the input...
> When you get a moment please review: 
> http://wiki.povray.org/content?title=Special:RecentChanges&hidebots=0

http://wiki.povray.org/content/Reference:Object_Modifiers
---------------------------------------------------------

---
Where we start with:

"Some conditions can produce unexpected results."

is there a way to make it a note? "Note..."

---
I don't know looking at the next sentence / list again...

"When applied to CSG components these modifiers work as expected: All 
Transforms, inverse, bounded_by, clipped_by, cutaway_textures, 
Hierarchy, and sturm."

What do you think about striking that sentence and only listing the next 
items that mostly don't get passed through CSG - except where we have 
unions not using split_unions off? I was trying to list things where I 
thought people might wonder whether they make it through CSG, but maybe 
it's just more confusing to do this?

I mean, I didn't list textures{} interior_texture{}, etc mostly because 
I think folks know or quickly learn how those work in CSG. They get 
attached to surfaces and do propagate through CSG except to the extent
those surfaces are seen in the resultant CSG (and cutaway_textures use).

Maybe your first take on a simpler statement with a list for what 
doesn't always make it through CSG is more understandable?

---
We list "Hierarchy" and it doesn't get highlighted with a link perhaps 
due the upper case H ?

---
Perhaps reword the sentence:

"Setting split_union off provides the exception with unions and their 
accepting unions."

as

"CSG unions pass all modifiers listed above unless split_union off has 
been set in which case the later list is ignored as with difference, 
intersection and merge."

---
Could we start a new paragraph before:

"Interiors get attached to the objects where interiors are defined."

Starting that paragraph with:

"While not technically object modifiers, object interior blocks and 
finish subsurface blocks see similar CSG propagation complications. 
Interiors get attached"

---
Where we have:

"In the case of subsurface,"

Perhaps change that to:

"Further, in the case of subsurface, ..."

---
Suppose:

"See also: All Transforms translate, rotate and scale"

technically includes too: matrix and transform{}.

---


Thanks for working on this.

Bill P.


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From: Jim Holsenback
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 27 Mar 2020 16:36:13
Message: <5e7e63bd@news.povray.org>
On 3/27/20 9:58 AM, William F Pokorny wrote:
> Thanks for working on this.

you are correct... in this case less is more.

http://wiki.povray.org/content/Reference:Object_Modifiers


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 27 Mar 2020 23:48:22
Message: <5e7ec906$1@news.povray.org>
On 3/27/20 4:36 PM, Jim Holsenback wrote:
> On 3/27/20 9:58 AM, William F Pokorny wrote:
>> Thanks for working on this.
> 
> you are correct... in this case less is more.
> 
> http://wiki.povray.org/content/Reference:Object_Modifiers
> 
Yes. I think that latest looks good.

My head keeps coming up with more questions about what might and might 
not work. But to test and enumerate all the fringe cases - ugh. And the 
detail would only confuse.

Thanks again.

Bill P.


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From: Bald Eagle
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 28 Mar 2020 10:00:00
Message: <web.5e7f57a1a6ce555cfb0b41570@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

> My head keeps coming up with more questions about what might and might
> not work. But to test and enumerate all the fringe cases - ugh. And the
> detail would only confuse.

Just asking out of curiosity - is there any way to flowchart most of this?
I often have a hard time deciphering the docs - because that's the nature of
documentation and language in general - but when there's a diagram or rendered
code example, to support the text, then it's usually much better.

Perhaps there's some debugging lines that can be inserted into a copy of the
source that will spit out how the stack of CSG onion layers gets "flattened".

Perhaps a simple POV-Ray scene that diagrammatically shows the "before" and
"after"  flattening attributes of CSG components just to illustrate the basic
concept graphically.


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 29 Mar 2020 10:41:11
Message: <5e80b387$1@news.povray.org>
On 3/28/20 9:56 AM, Bald Eagle wrote:
> 
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 
>> My head keeps coming up with more questions about what might and might
>> not work. But to test and enumerate all the fringe cases - ugh. And the
>> detail would only confuse.
> 
> Just asking out of curiosity - is there any way to flowchart most of this?

Probably. "It's only a matter of code," as an old work friend would say. :-)

> I often have a hard time deciphering the docs - because that's the nature of
> documentation and language in general - but when there's a diagram or rendered
> code example, to support the text, then it's usually much better.
> 
> Perhaps there's some debugging lines that can be inserted into a copy of the
> source that will spit out how the stack of CSG onion layers gets "flattened".
> 
> Perhaps a simple POV-Ray scene that diagrammatically shows the "before" and
> "after"  flattening attributes of CSG components just to illustrate the basic
> concept graphically.
> 

I'm with you on learning best from examples and diagrams. It's on my 
list to dig more into the bounding / final internal representations 
given I have a list of situations these days where bounding - or lack of 
good bounding - is the largest component of a scenes render time.

I've wanted too, to be able to dump the internal representation after 
parse and bounding, but no idea when I'll get something like that going. 
At the moment focused on the pattern/function cleanup I was working on 
late last year - but now in my cut down version of POV-Ray / povr.

Bill P.


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 29 Mar 2020 11:44:19
Message: <5e80c253$1@news.povray.org>
On 3/25/20 8:05 AM, William F Pokorny wrote:
...
> 
> I've got a little buzzer going off that somewhere in the last few years 
> Christoph responded to someone hitting a particular hollow issue with it 
> propagating or not as desired. I'll try and find that post.
> 

On my initial search I couldn't find anything, but just now, while 
creating a list of github issues and pull requests my cut down POV-Ray 
addresses or fixes, I ran across:

object hierarchy changes hollow set flag #307

  https://github.com/POV-Ray/povray/issues/307

For reference. Looks like whether and how hollow works or not is change 
v36 to v37 and complicated. Avoiding propagation through CSG still seems 
to me the safest bet.

Bill P.


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 29 Mar 2020 12:05:24
Message: <5e80c744$1@news.povray.org>
On 3/29/20 11:44 AM, William F Pokorny wrote:
> On 3/25/20 8:05 AM, William F Pokorny wrote:
> ...
> 
And a few more for the record:

---
Port of FS183 - cutaway_textures broken with child unions
#207

https://github.com/POV-Ray/povray/issues/207

---
Port of FS115 - More cutaway_textures. Difference color inheritance 
wrong. #196

https://github.com/POV-Ray/povray/issues/196

Unsure I agree with the conclusion of others in this one of it being a 
bogus result... This sort of override happens all the time of object {}, 
if a user wants the cutaway_textures to work they should not create a 
new overriding texture - or maybe I'm missing something.

Bill P.


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From: William F Pokorny
Subject: Re: no_image ignored in nested (difference > union > object)CSGmember
Date: 4 Apr 2020 06:00:56
Message: <5e885ad8$1@news.povray.org>
On 3/29/20 12:05 PM, William F Pokorny wrote:
> On 3/29/20 11:44 AM, William F Pokorny wrote:
>> On 3/25/20 8:05 AM, William F Pokorny wrote:
>> ...
> 
> 
  Yep, my head never shuts off on this stuff - a problem when it comes 
to getting anything in particular done. I wondered this morning about 
no_bump_scale and how it gets handled with normals...

The first paragraph of section 3.6.1.2.4 Scaling normals ends with the 
sentence: "Think of this like the way no_shadow gets passed on to 
objects contained in a CSG." which we know not to be generally true 
today in v3.7 or v3.8 - and I expect never completely true.

However, seeing that comment got me thinking about Christoph's statement 
about hollow treatments changing v36 to v37 with respect to which shape 
in a CSG was used to propagate hollow statements to a CSG result 
changing from the first to last - or maybe visa versa.

"Maybe," we could support some limited universal propagation of 
no_shadow et al through csg by always propagating always from ONLY the 
first object in the csg block? Is this what the pre - v37 coders intended?

In any case. If someone gets the time to dig. Maybe something limited 
like a first shape only csg propagation could be supported in v38 which 
would be of some help.

Bill P.


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