"Mike Miller" <mil### [at] gmailcom> wrote:

> I found the problem. It turns out that if add even a small amount of turbulence
> (.3 or more) to the fog definition - it tints the alpha portion of the image
> map. I set the turbulence to zero and it cleared it up. I'm not sure why, but it
> worked.

I would guess that it's probably not so much that it "tints" the transparent
portion as it patterns it in a way that the applied turbulence causes it to
mis-match the more distant parts of the scene.

Glad you got it to work out - things like that can drive you crazy.

- BW

Post a reply to this message

"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Mike Miller" <mil### [at] gmailcom> wrote:
>
> > I found the problem. It turns out that if add even a small amount of turbulence
> > (.3 or more) to the fog definition - it tints the alpha portion of the image
> > map. I set the turbulence to zero and it cleared it up. I'm not sure why, but it
> > worked.
>
> I would guess that it's probably not so much that it "tints" the transparent
> portion as it patterns it in a way that the applied turbulence causes it to
> mis-match the more distant parts of the scene.
>
> Glad you got it to work out - things like that can drive you crazy.
>
> - BW

Thanks,
your deduction makes sense...and yes, it was driving me crazy. :)
Mike.

Post a reply to this message

On 11/3/23 21:35, Mike Miller wrote:
> I found the problem. It turns out that if add even a small amount of turbulence
> (.3 or more) to the fog definition - it tints the alpha portion of the image
> map. I set the turbulence to zero and it cleared it up. I'm not sure why, but it
> worked.

Thanks for the update. Probably true in the official implementations of 
fog too, but my in my re-write of it, I left a comment that turbulence 
affects short length ray results much more than longer ones.

In any case, glad you are on your way.

Bill P.

Post a reply to this message

Op 3-11-2023 om 17:49 schreef Mike Miller:
> After taking some time off from POV, I'm ready to tackle a few new scenes I have
> in mind. One involves a landscape with some foreground vegetation. I started
> collecting some 2D sprite images of moss, grasses, and weeds thinking that I
> could populate the ground with them. I've run into a problem with the
> transparent portion of the png when turning on fog. The fog is tinting the
> billboard shape. I've removed the finish and have tried a variety of things in
> the shader with no success. I can fall back on 3D models if I can't get the
> sprites to work.  Below is what I used to texture this example. I understand
> that the bump statement will not have much of an effect without a finish. Any
> help would be appreciated.
> Thanks,
> Mike.
> 

No /help/ from this side, just the (historical) mention that this 
particular fog problem has been around since... prehistory. I first hit 
it, I think, sometime in the late '90's or early '20's when I tried to 
do exactly what you want to do. At the time I was also directed to use 
media instead of fog. Otherwise, there was no satisfying workaround.

-- 
Thomas

Post a reply to this message

Thomas de Groot <tho### [at] degrootorg> wrote:
> Op 3-11-2023 om 17:49 schreef Mike Miller:
> > After taking some time off from POV, I'm ready to tackle a few new scenes I have
> > in mind. One involves a landscape with some foreground vegetation. I started
> > collecting some 2D sprite images of moss, grasses, and weeds thinking that I
> > could populate the ground with them. I've run into a problem with the
> > transparent portion of the png when turning on fog. The fog is tinting the
> > billboard shape. I've removed the finish and have tried a variety of things in
> > the shader with no success. I can fall back on 3D models if I can't get the
> > sprites to work.  Below is what I used to texture this example. I understand
> > that the bump statement will not have much of an effect without a finish. Any
> > help would be appreciated.
> > Thanks,
> > Mike.
> >
>
> No /help/ from this side, just the (historical) mention that this
> particular fog problem has been around since... prehistory. I first hit
> it, I think, sometime in the late '90's or early '20's when I tried to
> do exactly what you want to do. At the time I was also directed to use
> media instead of fog. Otherwise, there was no satisfying workaround.
>
> --
> Thomas

Same...I do remember trying this before back in the day. I guess I always use a
touch of fog in my scenes. It looks like turbulence 0 in the fog statement
works.
Mike.

Post a reply to this message

Op 04/11/2023 om 16:10 schreef Mike Miller:
> Thomas de Groot <tho### [at] degrootorg> wrote:
>> Op 3-11-2023 om 17:49 schreef Mike Miller:
>>> After taking some time off from POV, I'm ready to tackle a few new scenes I have
>>> in mind. One involves a landscape with some foreground vegetation. I started
>>> collecting some 2D sprite images of moss, grasses, and weeds thinking that I
>>> could populate the ground with them. I've run into a problem with the
>>> transparent portion of the png when turning on fog. The fog is tinting the
>>> billboard shape. I've removed the finish and have tried a variety of things in
>>> the shader with no success. I can fall back on 3D models if I can't get the
>>> sprites to work.  Below is what I used to texture this example. I understand
>>> that the bump statement will not have much of an effect without a finish. Any
>>> help would be appreciated.
>>> Thanks,
>>> Mike.
>>>
>>
>> No /help/ from this side, just the (historical) mention that this
>> particular fog problem has been around since... prehistory. I first hit
>> it, I think, sometime in the late '90's or early '20's when I tried to
>> do exactly what you want to do. At the time I was also directed to use
>> media instead of fog. Otherwise, there was no satisfying workaround.
>>
>> --
>> Thomas
> 
> Same...I do remember trying this before back in the day. I guess I always use a
> touch of fog in my scenes. It looks like turbulence 0 in the fog statement
> works.
> Mike.
> 
Yes, that seems a nice workaround indeed. Very strange. I do not 
recollect that it was mentioned at the time; probably not...

Note to self: add a note to Notes... ;-)

-- 
Thomas

Post a reply to this message

On 11/5/23 02:07, Thomas de Groot wrote:
> Yes, that seems a nice workaround indeed. Very strange. I do not 
> recollect that it was mentioned at the time; probably not...
> 
> Note to self: add a note to Notes... 😉

Probably being redundant, but suppose I'll say, don't take the no 
turbulence patch as too much of a general fix.

It may work in Mike's scene; I couldn't pick up a seam during a quick 
check with gimp.

However, if we make the fog distance much more shallow or set the color 
really large it should be we start to see exactly the scenario Alain 
suggested where the space between billboards appears much more clouded 
than the clear parts of the billboard do.

Bill P.

Post a reply to this message

Op 06/11/2023 om 16:26 schreef William F Pokorny:
> On 11/5/23 02:07, Thomas de Groot wrote:
>> Yes, that seems a nice workaround indeed. Very strange. I do not 
>> recollect that it was mentioned at the time; probably not...
>>
>> Note to self: add a note to Notes... 😉
> 
> Probably being redundant, but suppose I'll say, don't take the no 
> turbulence patch as too much of a general fix.
> 
> It may work in Mike's scene; I couldn't pick up a seam during a quick 
> check with gimp.
> 
> However, if we make the fog distance much more shallow or set the color 
> really large it should be we start to see exactly the scenario Alain 
> suggested where the space between billboards appears much more clouded 
> than the clear parts of the billboard do.
> 
> Bill P.

Thanks, yes, I was aware of that indeed. In fact, I do not use fog very 
much any more and prefer media instead...

-- 
Thomas

Post a reply to this message

"Mike Miller" <mil### [at] gmailcom> wrote:
>
> I found the problem. It turns out that if add even a small amount of turbulence
> (.3 or more) to the fog definition - it tints the alpha portion of the image
> map. I set the turbulence to zero and it cleared it up. I'm not sure why, but it
> worked.

Yeah, that's a strange problem; I'm glad you found a solution.

> #declare sprite = box {<-.5,0,-.01>,<.5,1,.01> } ;
> object { sprite material {M_grass_A} scale <30,40,1> translate <0,-1,0>}

Just thought I would mention that you can make a box object with zero thickness,
which might be better for billboards. I usually use that trick.

#declare sprite = box {<-.5,0,0>,<.5,1,0> };

I wonder if that would have any effect on your original problem.

--------
A box can't be *scaled* to have zero-thickness, but it can be made that way
initially.

Post a reply to this message

"Kenneth" <kdw### [at] gmailcom> wrote:
> "Mike Miller" <mil### [at] gmailcom> wrote:
> >
> > I found the problem. It turns out that if add even a small amount of turbulence
> > (.3 or more) to the fog definition - it tints the alpha portion of the image
> > map. I set the turbulence to zero and it cleared it up. I'm not sure why, but it
> > worked.
>
> Yeah, that's a strange problem; I'm glad you found a solution.
>
> > #declare sprite = box {<-.5,0,-.01>,<.5,1,.01> } ;
> > object { sprite material {M_grass_A} scale <30,40,1> translate <0,-1,0>}
>
> Just thought I would mention that you can make a box object with zero thickness,
> which might be better for billboards. I usually use that trick.
>
> #declare sprite = box {<-.5,0,0>,<.5,1,0> };
>
> I wonder if that would have any effect on your original problem.
>
> --------
> A box can't be *scaled* to have zero-thickness, but it can be made that way
> initially.

Thanks,
Good to know. I ended up using a sphere intersected with a plane for most of the
curved leaves. I'll give the zero-depth box a try for a true billboard.
Miller

Post a reply to this message