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15 Jun 2024 10:49:09 EDT (-0400)
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From: Timwi
Subject: Bug in rendering of Bézier_patches
Date: 21 Mar 2013 16:41:21
Message: <514b7071$1@news.povray.org>
Hi!


patches in which four points (along one edge) are all the same point.

The rendering can be seen here:
	http://i.imgur.com/eq2UIXR.png

As you can see, there is a visible unwanted artifact in the corner of 
each patch. The two patches shown are essentially the same, except with 



Expected rendering is a smooth surface without the artifact.

Below is the code used to render the above example.

Thanks
Timwi




#version 3.7;

global_settings { assumed_gamma 1.0 }

camera {
     location <45, 31, -10>
     look_at <40, 21, 200>
     right x*image_width/image_height
}

light_source {
     <660, 300, -525>
     color rgb 1
}

// Example 1: First point in each row is the same point
bicubic_patch {
     type 1 flatness 0.001
     u_steps 4 v_steps 4
     <32.2168, -23.78125, 0>, <34.4968, -23.78125, 0>, <35.2168, 
-23.78125, -0.72>, <35.2168, -23.78125, -3>,
     <32.2168, -23.78125, 0>, <34.4968, -22.10256, 0>, <35.2168, 
-21.57244, -0.72>, <35.2168, -21.57244, -3>,
     <32.2168, -23.78125, 0>, <33.9709, -21.55577, 0>, <34.52483, 
-20.85299, -0.72>, <34.52483, -20.85299, -3>,
     <32.2168, -23.78125, 0>, <32.30556, -21.50298, 0>, <32.33359, 
-20.78352, -0.72>, <32.33359, -20.78352, -3>
     rotate 180*x

     scale 1.4
     translate <-5, 0, 0>
     pigment { color <1, 0, 0> }
}

// Example 2: First row is all the same point
bicubic_patch {
     type 1 flatness 0.001
     u_steps 4 v_steps 4
     <32.2168, -23.78125, 0>, <32.2168, -23.78125, 0>, <32.2168, 
-23.78125, 0>, <32.2168, -23.78125, 0>,
     <34.4968, -23.78125, 0>, <34.4968, -22.10256, 0>, <33.9709, 
-21.55577, 0>, <32.30556, -21.50298, 0>,
     <35.2168, -23.78125, -0.72>, <35.2168, -21.57244, -0.72>, 
<34.52483, -20.85299, -0.72>, <32.33359, -20.78352, -0.72>,
     <35.2168, -23.78125, -3>, <35.2168, -21.57244, -3>, <34.52483, 
-20.85299, -3>, <32.33359, -20.78352, -3>
     rotate 180*x

     scale 1.4
     pigment { color <1, 1, 0> }
}


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From: clipka
Subject: Re: Bug in rendering of Bézier_patches
Date: 23 Mar 2013 19:28:58
Message: <514e3aba@news.povray.org>
Am 21.03.2013 21:41, schrieb Timwi:


> patches in which four points (along one edge) are all the same point.

I'm not sure whether this actually qualifies as a bug, or just a 
limitation. After all, that one point does constitute a singularity.

At any rate, this issue has been around for ages now - I recall having 
stumbled across this problem when toying around with POV-Ray's bezier 
patches back in the mid-90's.

Could you please file an issue report at http://bugs.povray.org?


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From: Timwi
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 09:10:03
Message: <514efb2b$1@news.povray.org>
On 24/03/2013 00:28, clipka wrote:
>
> I'm not sure whether this actually qualifies as a bug, or just a
> limitation. After all, that one point does constitute a singularity.



not change that fact, and most users will expect it to render properly.

> Could you please file an issue report at http://bugs.povray.org?


fix it.

Timwi


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From: James Holsenback
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 10:37:36
Message: <514f0fb0@news.povray.org>
On 03/24/2013 09:10 AM, Timwi wrote:
> On 24/03/2013 00:28, clipka wrote:
>>
>> I'm not sure whether this actually qualifies as a bug, or just a
>> limitation. After all, that one point does constitute a singularity.
>


> not change that fact, and most users will expect it to render properly.
>
>> Could you please file an issue report at http://bugs.povray.org?
>

> fix it.
>
> Timwi
>
The "Edit this task" button on the lower left hand side of the "Details" 
area?


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From: Timwi
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 12:16:31
Message: <514f26df$1@news.povray.org>
On 24/03/2013 15:37, James Holsenback wrote:
> On 03/24/2013 09:10 AM, Timwi wrote:
>

>> fix it.
>
> The "Edit this task" button on the lower left hand side of the "Details"
> area?

There is none. http://screencast.com/t/YgGMFEcSWtn

I think someone should fix that.

Timwi


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From: James Holsenback
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 12:26:43
Message: <514f2943$1@news.povray.org>
On 03/24/2013 12:16 PM, Timwi wrote:
> On 24/03/2013 15:37, James Holsenback wrote:
>> On 03/24/2013 09:10 AM, Timwi wrote:
>>

>>> fix it.
>>
>> The "Edit this task" button on the lower left hand side of the "Details"
>> area?
>
> There is none. http://screencast.com/t/YgGMFEcSWtn
>
> I think someone should fix that.
>
> Timwi

I believe you have to be logged in to see that ... I hopped over there 
and didn't log-in. Indeed it's missing in that case.


Post a reply to this message

From: Timwi
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 13:44:11
Message: <514f3b6b$1@news.povray.org>
On 24/03/2013 17:26, James Holsenback wrote:
> On 03/24/2013 12:16 PM, Timwi wrote:
>> On 24/03/2013 15:37, James Holsenback wrote:
>>> On 03/24/2013 09:10 AM, Timwi wrote:
>>>

>>>> fix it.
>>>
>>> The "Edit this task" button on the lower left hand side of the "Details"
>>> area?
>>
>> There is none. http://screencast.com/t/YgGMFEcSWtn
>>
>> I think someone should fix that.
>
> I believe you have to be logged in to see that ... I hopped over there
> and didn't log-in. Indeed it's missing in that case.




I would bet that you have some sort of elevated privileges that allow 
you to edit /any/ bug. Whoever is adminning this simply forgot to allow 
bug submitters to edit /their own/ bugs.

Timwi


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From: James Holsenback
Subject: Re: Bug in rendering of Bézier_patches
Date: 24 Mar 2013 15:34:10
Message: <514f5532$1@news.povray.org>
On 03/24/2013 01:44 PM, Timwi wrote:
> On 24/03/2013 17:26, James Holsenback wrote:
>> On 03/24/2013 12:16 PM, Timwi wrote:
>>> On 24/03/2013 15:37, James Holsenback wrote:
>>>> On 03/24/2013 09:10 AM, Timwi wrote:
>>>>

>>>>> fix it.
>>>>
>>>> The "Edit this task" button on the lower left hand side of the
>>>> "Details"
>>>> area?
>>>
>>> There is none. http://screencast.com/t/YgGMFEcSWtn
>>>
>>> I think someone should fix that.
>>
>> I believe you have to be logged in to see that ... I hopped over there
>> and didn't log-in. Indeed it's missing in that case.
>


>
> I would bet that you have some sort of elevated privileges that allow
> you to edit /any/ bug. Whoever is adminning this simply forgot to allow
> bug submitters to edit /their own/ bugs.
>
> Timwi
>
I'm not saying you're wrong ... but not allowing a user to edit their 
own bug just doesn't make sense, and I believe the configure has been 
working just fine in the past. I'm fairly sure that would have been a 
problem long before now if it weren't


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From: Le Forgeron
Subject: Re: Bug in rendering of Bézier patches
Date: 25 Mar 2013 03:55:34
Message: <515002f6$1@news.povray.org>
Le 24/03/2013 20:34, James Holsenback a écrit :

> I'm not saying you're wrong ... but not allowing a user to edit their
> own bug just doesn't make sense, and I believe the configure has been
> working just fine in the past. I'm fairly sure that would have been a
> problem long before now if it weren't

There is a preview link before committing. If you do not use it to see
that the formatting is wrong (it happened to me, where some code was
interpreted as flyspray syntax for note...), just blame yourself and
correct with an additional comment.

Editing text is dangerous for efficiency: one would look at the bug on
the 1st January with one description, and by the 15th March the
description would have been changed to something different. You do not
build a house on moving sand.

-- 
Just because nobody complains does not mean all parachutes are perfect.


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From: clipka
Subject: Re: Bug in rendering of Bézier_patches
Date: 25 Mar 2013 09:05:10
Message: <51504b86@news.povray.org>
Am 24.03.2013 14:10, schrieb Timwi:
> On 24/03/2013 00:28, clipka wrote:
>>
>> I'm not sure whether this actually qualifies as a bug, or just a
>> limitation. After all, that one point does constitute a singularity.
>


> not change that fact, and most users will expect it to render properly.

A bug is something that is supposed to work but doesn't.

A limitation is something that was never supposed to work in the first 
place.

The Bezier patch is intended for square patches, and wasn't designed 
with triangular ones in mind. Therefore, if it doesn't work with 
triangular patches, it would be fair to call it a limitation rather than 
a bug.

As I said, I myself am not sure how I'd categorize it. My favored 
approach to this issue would be to provide some kind of dedicated 
triangular bezier patch for such use cases, but so far I haven't managed 
to come up with consistent math for such an animal.


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