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From: Mike Horvath
Subject: LDraw user needs POV help
Date: 16 Nov 2016 22:06:27
Message: <582d1eb3$1@news.povray.org>
Could someone take a look at this forum thread and help the user learn 
to use POV-Ray properly?

http://forums.ldraw.org/showthread.php?tid=21710&pid=23858&mode=threaded

Thanks.

Mike


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From: Mike Horvath
Subject: Re: LDraw user needs POV help
Date: 17 Nov 2016 06:41:38
Message: <582d9772$1@news.povray.org>
On 11/16/2016 10:06 PM, Mike Horvath wrote:
> Could someone take a look at this forum thread and help the user learn
> to use POV-Ray properly?
>
> http://forums.ldraw.org/showthread.php?tid=21710&pid=23858&mode=threaded
>
> Thanks.
>
> Mike

Sorry, I should have instead suggested that I relay your tips to him 
myself. I told him to come here, but he has not done so yet.

Mike


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From: Mike Horvath
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 16:01:27
Message: <582f6c27$1@news.povray.org>
On 11/17/2016 6:41 AM, Mike Horvath wrote:
> On 11/16/2016 10:06 PM, Mike Horvath wrote:
>> Could someone take a look at this forum thread and help the user learn
>> to use POV-Ray properly?
>>
>> http://forums.ldraw.org/showthread.php?tid=21710&pid=23858&mode=threaded
>>
>> Thanks.
>>
>> Mike
>
> Sorry, I should have instead suggested that I relay your tips to him
> myself. I told him to come here, but he has not done so yet.
>
> Mike

I would appreciate some help here. The developer insists that he needs 
to set assumed_gamma to 2.2 and use emission on all pigments. He is not 
migrating scenes from POV 3.6

Mike


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From: clipka
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 16:30:54
Message: <582f730e@news.povray.org>
Am 18.11.2016 um 22:01 schrieb Mike Horvath:
> On 11/17/2016 6:41 AM, Mike Horvath wrote:
>> On 11/16/2016 10:06 PM, Mike Horvath wrote:
>>> Could someone take a look at this forum thread and help the user learn
>>> to use POV-Ray properly?
>>>
>>> http://forums.ldraw.org/showthread.php?tid=21710&pid=23858&mode=threaded
>>>
>>> Thanks.
>>>
>>> Mike
>>
>> Sorry, I should have instead suggested that I relay your tips to him
>> myself. I told him to come here, but he has not done so yet.
>>
>> Mike
> 
> I would appreciate some help here. The developer insists that he needs
> to set assumed_gamma to 2.2 and use emission on all pigments. He is not
> migrating scenes from POV 3.6

I had hoped that some other user more familiar with LDraw than me would
chime in; seeing that is not the case, I'll have a look what suggestions
I can come up with.


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From: Roland Melkert
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 16:55:00
Message: <web.582f776da94cadc5369a059c0@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:
> On 11/16/2016 10:06 PM, Mike Horvath wrote:
> > Could someone take a look at this forum thread and help the user learn
> > to use POV-Ray properly?
> >
> > http://forums.ldraw.org/showthread.php?tid=21710&pid=23858&mode=threaded
> >
> > Thanks.
> >
> > Mike
>
Hello all, I'm that user :)

The main problem I'm having is mixing multiple texture blocks to mimic the LDraw
OpenGL rendering.

I was expecting the multiple layers to 'inherit' things from the lower textures
so if you have a red pigment with some reflection etc and add a image_map
texture on top of that it would result in a surface with the top level textures
properties but with the png blended on top.

I hope this is somewhat understandable from non LDraw users.

See this post for an OpenGL comparison with the current exported results.

http://forums.ldraw.org/thread-21710-post-23886.html#pid23886


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From: clipka
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 18:13:10
Message: <582f8b06$1@news.povray.org>
Am 18.11.2016 um 22:49 schrieb Roland Melkert:

> Hello all, I'm that user :)

Welcome to the POV-Ray newsgroups :)

> The main problem I'm having is mixing multiple texture blocks to mimic the LDraw
> OpenGL rendering.

Is that really what you want? I mean, the fact that you're using
something different than OpenGL is a clear indication that you're not
happy with the OpenGL results... or am I missing something?

So you should never ask, "does that mimic the LDraw OpenGL rendering",
but "does that look realistic".


> I was expecting the multiple layers to 'inherit' things from the lower textures
> so if you have a red pigment with some reflection etc and add a image_map
> texture on top of that it would result in a surface with the top level textures
> properties but with the png blended on top.

In POV-Ray, layered textures do not inherit anything from other textures
in the stack. Each has its own independent finish properties. It is also
important to note that wherever lower layers peep through, finish
effects such as specular highlights and reflections from both layers are
added.

Layered textures therefore tend to be difficult to control. If possible,
I'd recommend using texture maps (they tend to be slower though). You
can use the alpha channel of an image to choose between two textures,
and then use the colour channel of the same image for one of them. Let
me know if you need help with the details.

That said, maybe I can add a switch to layered textures in POV-Ray that
would cause the alpha channel of a layer to knock out not only that
layer's diffuse component, but also highlights and reflection. I guess
such a switch might come in handy for non-LDraw users as well.

I hope I am making sense to you, and am barking up the right tree. If
not, let me know.


> I hope this is somewhat understandable from non LDraw users.
> 
> See this post for an OpenGL comparison with the current exported results.
> 
> http://forums.ldraw.org/thread-21710-post-23886.html#pid23886

Looks pretty convincing to me. What bothers you about it specifically?


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From: Roland Melkert
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 19:25:06
Message: <web.582f9ab2a94cadc5369a059c0@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Welcome to the POV-Ray newsgroups :)
I actually already had an account (for years) I just completely forgot about it.

> Is that really what you want? I mean, the fact that you're using
> something different than OpenGL is a clear indication that you're not
> happy with the OpenGL results... or am I missing something?
I was trying to mimic the inheritance you get when using LDraw parts as they
only have one mesh per part which can be used in any color. In OpenGL this is
done by blending the triangle color with an alpha enabled texture. But reading
your comments here and on LDraw.org I think I need to look into texture_map for
that.

> In POV-Ray, layered textures do not inherit anything from other textures
> in the stack. Each has its own independent finish properties. It is also
> important to note that wherever lower layers peep through, finish
> effects such as specular highlights and reflections from both layers are
> added.
I noticed this and ended up adding info on png's being transpaent or not to
generate different kinds of (layered) textures.

> Layered textures therefore tend to be difficult to control. If possible,
> I'd recommend using texture maps (they tend to be slower though). You
> can use the alpha channel of an image to choose between two textures,
> and then use the colour channel of the same image for one of them. Let
> me know if you need help with the details.
Thanks I'm going to look into that.

> That said, maybe I can add a switch to layered textures in POV-Ray that
> would cause the alpha channel of a layer to knock out not only that
> layer's diffuse component, but also highlights and reflection. I guess
> such a switch might come in handy for non-LDraw users as well.
That would be very helpful especially when coming from an OpenGL background.

>
> I hope I am making sense to you, and am barking up the right tree. If
> not, let me know.
Yes very much so, thanks.


> > http://forums.ldraw.org/thread-21710-post-23886.html#pid23886
>
> Looks pretty convincing to me. What bothers you about it specifically?
Mainly the fact the non transparent part of the image_map isn't transparent on
transparent part usage. The difference being patterns painted on transparent
plastic or them being part of the transparent plastic. I think both situations
can appear in real LEGO though so I'm not sure which one is correct. But for now
I want them to be the same as much as possible.

But I suspect texture_map can solve that too.


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From: clipka
Subject: Re: LDraw user needs POV help
Date: 18 Nov 2016 21:45:56
Message: <582fbce4@news.povray.org>
Am 19.11.2016 um 01:20 schrieb Roland Melkert:

>>> http://forums.ldraw.org/thread-21710-post-23886.html#pid23886
>>
>> Looks pretty convincing to me. What bothers you about it specifically?
> Mainly the fact the non transparent part of the image_map isn't transparent on
> transparent part usage. The difference being patterns painted on transparent
> plastic or them being part of the transparent plastic. I think both situations
> can appear in real LEGO though so I'm not sure which one is correct. But for now
> I want them to be the same as much as possible.

I /think/ you may need to try to explain that in a different manner
before I'll be able to grasp that...

Are you talking about the helmet's ornaments looking semi-transparent in
the OpenGL render, but opaque in the POV-Ray render?

To me the opaque ornaments look more convincing, as such features are
usually screen-printed on real-life LEGO parts with quite a good
coverage, rather than being a change in the transparent plastic's tint.

As a matter of fact producing truly multi-coloured plastic parts with a
reasonable degree of control over the distribution of colours is darn
complicated, and would probably be excessively expensive; so wherever
LEGO pieces are multi-coloured, they are either actually assemblies of
multiple parts, or uniformly-coloured parts with screen prints.

If you want a screen print to look imperfect, you can give it a bit of
transparency by blending the image_map (with alpha channel) with a
totally transparent pigment, for example using an average pattern. You
can even use some noisy pattern to model the imperfections and/or wear
typically seen with those screen prints.


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From: Mike Horvath
Subject: Re: LDraw user needs POV help
Date: 19 Nov 2016 11:36:44
Message: <58307f9c$1@news.povray.org>
On 11/18/2016 4:30 PM, clipka wrote:
> I had hoped that some other user more familiar with LDraw than me would
> chime in; seeing that is not the case, I'll have a look what suggestions
> I can come up with.
>

Thank you!


Mike


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From: Roland Melkert
Subject: Re: LDraw user needs POV help
Date: 19 Nov 2016 15:30:00
Message: <web.5830b62fa94cadc5369a059c0@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Are you talking about the helmet's ornaments looking semi-transparent in
> the OpenGL render, but opaque in the POV-Ray render?
Yes

> To me the opaque ornaments look more convincing, as such features are
> usually screen-printed on real-life LEGO parts with quite a good
> coverage, rather than being a change in the transparent plastic's tint.
Probably, I think I'm going to leave it for now as textured LDraw parts aren't
wide used anyway (so no real usage info).

> If you want a screen print to look imperfect, you can give it a bit of
> transparency by blending the image_map (with alpha channel) with a
> totally transparent pigment, for example using an average pattern. You
> can even use some noisy pattern to model the imperfections and/or wear
> typically seen with those screen prints.
That might take it a bit far for the initial exporter, but it certainly will be
something to think about for a revision later on :)


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