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From: William F Pokorny
Subject: Normal documentation images. Quilted.
Date: 11 Oct 2020 13:22:46
Message: <5f830726@news.povray.org>
Some days back, Bald Eagle, privately asked me about a comment in 
POV-Ray's source code. One mentioning floor() and the FLOOR() macro. The 
comment suggests the latter did some mirroring. After a wrong answer or 
two, I now believe FLOOR() was always about performance regardless of 
code comments - and so functionally not what the quilted coders expected.

With hexagon the two FLOOR() uses are buying performance. Plus, the 
results in that case are identical to floor() due the inputs being 
conditioned positive.

With quilted's FLOOR() use - in both implementations - it's harder to 
determine what's happening. With it, I think someone was expecting 
plus/minus axis mirroring - and not getting it.

I created quilted test cases and reviewed the shipped demo scenes. A 
number of other issues popped out. One of which is the 'true normal' 
results do not match what our documentation shows for quilted normals.

This led me to allnormals.pov which, IIRC, is used for the normal{} 
pattern images in the documentation. The set up is shown below and it's 
'wrong' as indicated for normal{ <true normal-pattern> } images(1)):

#declare Agate         = normal {pigment_pattern{agate
#WRONG   Average       = normal {pigment_pattern{average
#declare Boxed         = normal {pigment_pattern{boxed
#declare Bozo          = normal {pigment_pattern{bozo
#declare Brick         = normal {pigment_pattern{brick
#WRONG   Bumps         = normal {pigment_pattern{bumps
#declare Cells         = normal {pigment_pattern{cells
#declare Checker       = normal {pigment_pattern{checker
#declare Crackle       = normal {pigment_pattern{crackle
#declare Cylindrical   = normal {pigment_pattern{cylindrical
#WRONG   Dents         = normal {pigment_pattern{dents
#declare Mandel        = normal {pigment_pattern{mandel
#declare Julia         = normal {pigment_pattern{julia
#declare Facets        = normal {facets
#declare Function      = normal {pigment_pattern{function
#declare Gradient      = normal {pigment_pattern{gradient
#declare Granite       = normal {pigment_pattern{granite
#declare Hexagon       = normal {pigment_pattern{hexagon
#declare Image_pattern = normal {pigment_pattern{image_pattern
#declare Leopard       = normal {pigment_pattern{leopard
#declare Marble        = normal {pigment_pattern{marble
#declare Onion         = normal {pigment_pattern{onion
#declare Planar        = normal {pigment_pattern{planar
#WRONG   Quilted       = normal {pigment_pattern{quilted
#declare Radial        = normal {pigment_pattern{radial
#WRONG   Ripples       = normal {pigment_pattern{ripples
#declare Spherical     = normal {pigment_pattern{spherical
#declare Spiral1       = normal {pigment_pattern{spiral1
#declare Spiral2       = normal {pigment_pattern{spiral2
#declare Spotted       = normal {pigment_pattern{spotted
#WRONG   Waves         = normal {pigment_pattern{waves
#declare Wood          = normal {pigment_pattern{wood
#WRONG   Wrinkles      = normal {pigment_pattern{wrinkles

Why is allnormals.pov not showing the normal{} version of the pattern 
when there is one? (Excepting facets as there's no 'value for map' 
version of that pattern.)

The documentation today is confusing with respect to normal{} pattern use.

Where there is a normal specific version of the pattern, we have a 
trifecta of possible schemes/results. A 'value for map' pattern result 
such as used with a pigment map; A 'value for map' result where sampled 
pattern values are used to perturb the surface's normal vector; Lastly, 
a normal specific, 'perturbed normal vector' result.

(1) The html generated by allnormals.pov has the statement: "Most of the 
patterns, used as a normal." It could, thinly, be argued to be off the 
hook by taking pattern to mean the 'value for map' version of perturbed 
normals, but...

----
Attached is an image - generated with v3.8 master - showing additional 
quilted specific issues.

In the upper left is the 'value for map' pattern surface normal 
perturbation. Internally, the map pattern's value is sampled four times 
and those samples are used to perturb the shape's surface normal. The 
normal block's accuracy setting comes into play here. Beyond that, I've 
not worked through what the code is really doing.

In the upper right is today's (v3.7/v3.8) true normal { quilted ... } 
result. It shows one of the longstanding issues with the quilted normal 
perturbation implementation. Specifically, if the shape's surface 
"lands" on any of the texture's axial "floors" during texture 
evaluation, you get a noisy result.

The usual fix for that sort of problem is to apply a small positive or 
negative epsilon - somewhere - in the system being calculated so such 
landings are unlikely in practice. Checker does this internal to the 
pattern code. It's that epsilon adjustment I made too small back in 
March with povr changes. The quilted's true normal pattern leaves this 
epsilon value fudging to users.

In the lower left I shrunk the pattern by a tiny epsilon to nudge the 
system off the floor. The noise goes away on the negative x axis. The 
the perturbed normal vector also partly inverts! This another 
longstanding issue. One which happens over half of each unit interval 
along each axis.

In the lower right I expanded the pattern by a tiny epsilon. The noise 
is again gone on the -x surface. This time it looks 'quilted.'

Why is the -z face still seeing noise no matter the pattern scaling?

It's because the allnormals.pov template scene translates the shapes +z 
by an amount that puts the cube's front face on the 0.0, z, normal 
pattern floor during evaluation. To fix this face, one has to adjust 
that surface so it lands less unfortunately. The 0.0 position is a 
special case that pattern and shape sizing cannot fix.

By sizing a shape by epsilon we can get the perturbed normal polarity 
right for only half the cube surfaces at once. Fixing all six requires 
sizing, translation and particular placement in the quilted pattern.

Additionally, from other test cases, it looks to me like the quilted 
normal has a negative axis bias (no expected FLOOR() mirroring?). The 
depth/strength of the perturbed normals is not constant with axially 
perpendicular surface position. Non-symmetrical shapes are more 
complicated to position well in the pattern.

All said, I believe the normal perturbation quilted code can be tweaked 
to eliminate most (all?) of the issues.

There are fewer gotchas in the quilted 'value for map' pattern though 
one springs to mind.

The code has long set the quilted's default wave shaping frequency to 
0.0(2). I 'suspect' this was to avoid (now old to povr) wave shaping 
fudge factor artifacts. Anyway, the point being, the phase modifier 
doesn't work by default due this default - and that's not documented.

Further, anyone 'can' set frequency to something other than 0.0 and 
phase will suddenly be active again - as will the 0-1 fudge factor 
fmod-ing the frequency 0 setting is 'probably' hoping to avoid.

(2) - Yep, there's more that could be said here. This 'Easter egg,' sdl 
available mechanism is gone in povr.

I'll add, the 'value map' version of quilted isn't quilted in appearance.

---
For povr, my current plan is to make better the true normal perturbation 
quilted code and delete the quilted 'value for map' pattern. Quilted 
then to become like facets in normal behavior in having only a normal{} 
version. We'll see.

Bill P.


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From: Kenneth
Subject: Re: Normal documentation images. Quilted.
Date: 11 Oct 2020 20:05:06
Message: <web.5f836374cc1d58b6d98418910@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:
>
> In the upper right is today's (v3.7/v3.8) true normal { quilted ... }
> result. It shows one of the longstanding issues with the quilted normal
> perturbation implementation. Specifically, if the shape's surface
> "lands" on any of the texture's axial "floors" during texture
> evaluation, you get a noisy result.
>
> The usual fix for that sort of problem is to apply a small positive or
> negative epsilon - somewhere - in the system being calculated so such
> landings are unlikely in practice.

Thanks for looking into this. I have always suspected that the quilted pattern
(at least as a 'normal') has some unexpected quirks.

Back in April 2018, I actually posted an animation test about this, with some
notes; perhaps it would prove helpful...

http://news.povray.org/povray.binaries.animations/thread/%3Cweb.5ae6126fe8495210a47873e10%40news.povray.org%3E/

I too found that I needed to add a slight positioning 'fudge factor' to the
pattern in my SDL code (like your internal epsilon tweaking) to avoid the
'noise' that you described. I also think that the pattern has some kind of
'discontinuity'-- in other words, that it does not seem to be uniform in its
behavior throughout its unit(?)-cube spatial volume. The effect is hard to
describe; maybe my animation will make it clear. I had assumed that the pattern
'spread out' or expanded from a central point-- so that it would perturb all six
faces of a cube in an equal way; but the visual result looks...odd.


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From: William F Pokorny
Subject: Re: Normal documentation images. Quilted.
Date: 12 Oct 2020 11:08:16
Message: <5f843920$1@news.povray.org>
On 10/11/20 4:03 PM, Kenneth wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
>>
>> In the upper right is today's (v3.7/v3.8) true normal { quilted ... }
>> result. It shows one of the longstanding issues with the quilted normal
>> perturbation implementation. Specifically, if the shape's surface
>> "lands" on any of the texture's axial "floors" during texture
>> evaluation, you get a noisy result.
>>
>> The usual fix for that sort of problem is to apply a small positive or
>> negative epsilon - somewhere - in the system being calculated so such
>> landings are unlikely in practice.
> 
> Thanks for looking into this. I have always suspected that the quilted pattern
> (at least as a 'normal') has some unexpected quirks.
> 
> Back in April 2018, I actually posted an animation test about this, with some
> notes; perhaps it would prove helpful...
> 
>
http://news.povray.org/povray.binaries.animations/thread/%3Cweb.5ae6126fe8495210a47873e10%40news.povray.org%3E/
> 
> I too found that I needed to add a slight positioning 'fudge factor' to the
> pattern in my SDL code (like your internal epsilon tweaking) to avoid the
> 'noise' that you described. I also think that the pattern has some kind of
> 'discontinuity'-- in other words, that it does not seem to be uniform in its
> behavior throughout its unit(?)-cube spatial volume. The effect is hard to
> describe; maybe my animation will make it clear. I had assumed that the pattern
> 'spread out' or expanded from a central point-- so that it would perturb all six
> faces of a cube in an equal way; but the visual result looks...odd.
> 
> 

Hi. Thank you for the pointer. I missed your original post - or it got 
lost in my old noggin...

Aside: The video played, but was blank for me, until the last few frames 
on my raspbian last night. It's OK on this machine this morning. Who 
knows :-).

No doubt you found some of quilted's complications. I "think" I 
understand most of what's happening and why. We'll see.

I believe any updated code should 'perturb' with the original surface 
normal in mind. I see a path to do this with flat surface stuff like 
cubes, but I don't know how to do it for curved surfaces in normal.cpp.

The facets pattern has a curved surface method. I'll have to see if I 
can digest what was done there.

A simpler approach would be to warp normals constructed flat to common 
shapes. However, there's that block of un-finished normal warp / unwarp 
related code. I see it, but I don't really understand what works and 
doesn't with normals tangled in warps.

Truth is, I don't use normals that often. My todo list is effectively 
infinite. No promises as to when I can make things better with povr 
quilted normals. I'm about 95% sure I'll remove the value version of 
quilted from povr and replace it with 'seedfi' pattern(s?).

Bill P.


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From: Ash Holsenback
Subject: Re: Normal documentation images. Quilted.
Date: 12 Oct 2020 11:11:01
Message: <5f8439c5$1@news.povray.org>
On 10/11/20 9:22 AM, William F Pokorny wrote:
> This led me to allnormals.pov which, IIRC, is used for the normal{} 
> pattern images in the documentation. The set up is shown below and it's 
> 'wrong' as indicated for normal{ <true normal-pattern> } images(1)):

well i don't know / recall... perhaps t / d stamp can provide some 
guidance. the 1st link shows what is likely the initial load when wiki 
was being setup, the 2nd shows Jerome made a change... maybe his memory 
is better than mine!


http://wiki.povray.org/content/File:RefImgQuiltpt4.gif

http://wiki.povray.org/content/File:RefImgQuiltedNormal.png


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From: Ash Holsenback
Subject: Re: Normal documentation images. Quilted.
Date: 12 Oct 2020 11:18:23
Message: <5f843b7f$1@news.povray.org>
On 10/12/20 7:11 AM, Ash Holsenback wrote:
> On 10/11/20 9:22 AM, William F Pokorny wrote:
>> This led me to allnormals.pov which, IIRC, is used for the normal{} 
>> pattern images in the documentation. The set up is shown below and 
>> it's 'wrong' as indicated for normal{ <true normal-pattern> } images(1)):
> 
> well i don't know / recall... perhaps t / d stamp can provide some 
> guidance. the 1st link shows what is likely the initial load when wiki 
> was being setup, the 2nd shows Jerome made a change... maybe his memory 
> is better than mine!

lol... 11 and 6 years ago!!! holy crap... lately last week is ancient 
history. senility must be setting in


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From: Bald Eagle
Subject: Re: Normal documentation images. Quilted.
Date: 12 Oct 2020 18:40:01
Message: <web.5f84a1e0cc1d58b61f9dae300@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

> No doubt you found some of quilted's complications. I "think" I
> understand most of what's happening and why. We'll see.
>
> I believe any updated code should 'perturb' with the original surface
> normal in mind. I see a path to do this with flat surface stuff like
> cubes, but I don't know how to do it for curved surfaces in normal.cpp.

Maybe you could write a scene trying to express the quilted pattern in SDL as a
function?
Sometimes it's a bit difficult to translate the somewhat cryptic C++ syntax into
something intelligible.
Then at least you could have a few people play with the function and have more
eyes and minds analyzing how it all works, and where it goes wrong.

Including a note or two about how to translate the C++ to SDL (if possible)
would help future efforts, and people could begin to play with more of the
source code and patterns.   I have found this approach to be personally
educational, developmentally useful  (how many "bugs" have we found?), and it
inspires me to invent new derivative functions and patterns.


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From: Bald Eagle
Subject: Re: Normal documentation images. Quilted.
Date: 12 Oct 2020 23:45:01
Message: <web.5f84ea71cc1d58b61f9dae300@news.povray.org>
William F Pokorny <ano### [at] anonymousorg> wrote:

> I created quilted test cases and reviewed the shipped demo scenes. A
> number of other issues popped out. One of which is the 'true normal'
> results do not match what our documentation shows for quilted normals.

Perhaps I'm wrong or misreading something, but it doesn't appear that the
documentation properly describes the pattern.

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

Just looking at the last image,
"A control value of 1 at both ends will give an "s" shaped curve, resulting in a
softer, more rounded edge."
yet the solid line is the s-shaped curve, and it says for that c1 = 0.

After skimming through the source code in patterns and normals, the basic
formula used to generate the curve seems an awful lot like a specialized form of
bicubic spline with c0 and c1 influencing the internal two control points...

but it's ... bizarrely different.
And I can't reproduce the curves and s-shape reliably.
And I don't know why they don't use a function based on 2*x, or use mod(), ...


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From: Bald Eagle
Subject: Re: Normal documentation images. Quilted.
Date: 13 Oct 2020 02:50:00
Message: <web.5f851559cc1d58b61f9dae300@news.povray.org>
Pfft.
I rolled my own and came up with more or less the same curves, but the way the
parameters influence them is different (of course...).

Maybe I can adapt this into a pigment pattern and a normal.

Do we know who made, how, and where the files are for the illustrations at:
http://wiki.povray.org/content/Reference:Quilted_Pattern ?

That would be a huge help.


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From: William F Pokorny
Subject: Re: Normal documentation images. Quilted.
Date: 13 Oct 2020 07:57:11
Message: <5f855dd7@news.povray.org>
On 10/12/20 2:35 PM, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
...
> 
> Maybe you could write a scene trying to express the quilted pattern in SDL as a
> function?
> 
> Including a note or two about how to translate the C++ to SDL (if possible)
> would help future efforts, and people could begin to play with more of the
> source code and patterns.   
> 

Hmm. More automatic c++ -> sdl idea interesting. Some things wouldn't be 
doable at all, but certain stuff would be more or less - I guess. Busy 
with real life today and tomorrow won't leave me a lot of time, but I'll 
stick the idea in my head and start to let it bang around in there.

Bill P.


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From: William F Pokorny
Subject: Re: Normal documentation images. Quilted.
Date: 13 Oct 2020 08:06:50
Message: <5f85601a$1@news.povray.org>
On 10/12/20 7:44 PM, Bald Eagle wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 
>> I created quilted test cases and reviewed the shipped demo scenes. A
>> number of other issues popped out. One of which is the 'true normal'
>> results do not match what our documentation shows for quilted normals.
> 
> Perhaps I'm wrong or misreading something, but it doesn't appear that the
> documentation properly describes the pattern.
> 
> http://wiki.povray.org/content/Reference:Quilted_Pattern
> 
> Just looking at the last image,
> "A control value of 1 at both ends will give an "s" shaped curve, resulting in a
> softer, more rounded edge."
> yet the solid line is the s-shaped curve, and it says for that c1 = 0.
> 
> After skimming through the source code in patterns and normals, the basic
> formula used to generate the curve seems an awful lot like a specialized form of
> bicubic spline with c0 and c1 influencing the internal two control points...
> 
> but it's ... bizarrely different.
> And I can't reproduce the curves and s-shape reliably.
> And I don't know why they don't use a function based on 2*x, or use mod(), ...
> 

Yes, I'm not quite sure what's going on there either.

Though I specified defaults of 1 and 1 it looked to me more like 1 and 0 
or 0 and 1 depending on how the normals flip on the half unit 
intervals... I didn't dive into it. ;-)

One of the complications is the curves as shown have one value inputs. 
The result we 'see' is a combination of three applications to three 
input values. Ahhh, as I expect you know! :-)

Bill P.


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