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MathGroup Archive 2007

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Re: Re: Anomalous behaviour of Penrose Triangle Demonstration


Thanks to Curtis & Gary for their replies.

  I hope someone at WRI is following this thread because it certainly  
appears that we have a V6 graphics/driver bug identified here.

I hope a few more of the mathgroup run the code to give more  
diagnostic input for different OSs & hardware combinations.

My machine is a:-

Model Name:	        MacBook Pro 17"
Model Identifier:	MacBookPro2,1
Processor Name:	Intel Core 2 Duo

Graphics & driver info:

  Chipset Model:	ATY,RadeonX1600
   Type:	Display
   Bus:	PCIe
   VRAM (Total):	256 MB
   Vendor:	ATI (0x1002)
   Device ID:	0x71c5
   Revision ID:	0x0000
   ROM Revision:	113-xxxxxx-158
   EFI Driver Version:	01.00.158



Syd Geraghty

On Sep 13, 2007, at 3:32 AM, WetBlanket wrote:

> On Sep 12, 2:59 am, Curtis Osterhoudt <c... at lanl.gov> wrote:
>> Hi, Syd,
>>
>>    I have no real insight. I confirm that changing the ViewPoint  
>> prefactor
>> causes the same behavior on my machine. I did not try to evaluate  
>> the code
>> which allows "vp" to be changed via a slider; just rotating the  
>> graphic
>> produced by the first chunk of code causes part of it to disappear  
>> (somewhat
>> randomly).
>>     Of course, I've been having lots of problems with my ATI  
>> drivers not being
>> compatible with Mathematica 6.0's Graphics3D[] objects, so this  
>> may be a
>> symptom of that.
>>
>>    This is on "6.0 for Linux x86 (32-bit) (June 19, 2007)".
>>
>> On Tuesday 11 September 2007 03:23:52 you wrote:
>>
>>
>>
>>> I would appreciate some insight regarding the Penrose Triangle
>>> Demonstration which can be found at:-
>>
>>>            http://demonstrations.wolfram.com/PenroseTriangle/
>>
>>> The original source I downloaded when run on my machine displayed a
>>> blank panel!
>>> (The demonstration ran fine on my machine in "watch web preview"  
>>> mode!)
>>
>>> $Version    Out[1]= "6.0 for Mac OS X x86 (32-bit) (June 19, 2007)"
>>
>>> The demonstration source was;-
>>
>>> Manipulate[
>>>   cu[x_, y_, z_, d_] :=
>>>    Cuboid[ {x - d/2, y - d/2, z - d/2}, {x + d/2, y + d/2, z + d/ 
>>> 2} ];
>>>   Graphics3D[
>>>    {Opacity[o],
>>>     cu[0, 15, 30, 7.5], cu[15, 45, 0, 7.5],
>>>     Table[cu[0, 0, 15 n, 7.5], {n, 0, 3}],
>>>     Table[cu[0, 15 n, 0, 7.5], {n, 3}]
>>>     } ,
>>>          ViewPoint -> 200 {-1, -1, 1},
>>>          Boxed -> False,
>>>          PlotRange -> 50 {{-1, 0.8}, {-0.6, 1}, {-0.08, 1}},
>>>          ImageSize -> {400, 400}
>>>    ],
>>>         {{o, 1, "opacity"}, 0, 1}, TrackedSymbols :> Manipulate]
>>
>>> I changed the "viewpoint factor" in  ViewPoint -> 200 {-1, -1, 1}
>>> above to 100{-1, -1, 1} on a hunch and the panel
>>> displayed correctly.
>>
>>> After failing to find any documentation for the use of the  
>>> "viewpoint
>>> factor" I tried setting a range for vp and generating a slider in
>>> addition to opacity to see the effects.
>>
>>> Manipulate[
>>>   cu[x_, y_, z_, d_] :=
>>>    Cuboid[ {x - d/2, y - d/2, z - d/2}, {x + d/2, y + d/2, z + d/ 
>>> 2} ];
>>>   Graphics3D[
>>>    {Opacity[o],
>>>     cu[0, 15, 30, 7.5], cu[15, 45, 0, 7.5],
>>>     Table[cu[0, 0, 15 n, 7.5], {n, 0, 3}],
>>>     Table[cu[0, 15 n, 0, 7.5], {n, 3}]
>>>     } ,
>>>          ViewPoint -> vp {-1, -1, 1},
>>>          Boxed -> False,
>>>          PlotRange -> 50 {{-1, 0.8}, {-0.6, 1}, {-0.08, 1}},
>>>          ImageSize -> {400, 400}
>>>    ],
>>>         {{o, 1, "opacity"}, 0, 1}, {{vp, 10, "ViewPoint Factor"},  
>>> 10,
>>> 200, 10},
>>>    TrackedSymbols :> Manipulate]
>>
>>> The effects of using the vp slider are very odd. Bits of the graphic
>>> start disappearing!
>>
>>> Any clues as to what is happening here would be appreciated.
>>
>>> Yet another strange "feature" showed up when I tried to "Save As"  
>>> the
>>> modified demonstration code.
>>
>>> I cannot successfully save the modified demonstration.
>>
>>> I suspect that is a WRI safeguard for protecting the integrity of  
>>> the
>>> Demonstrations Project (which is fine by me).
>>
>>> I can of course save the modified code in a new blank notebook.
>>
>>> Syd Geraghty
>>
>> --
>> ==========================================================
>> Curtis Osterhoudt
>> cfo at remove_this.lanl.and_this.gov
>> PGP Key ID: 0x4DCA2A10
>> Please avoid sending me Word or PowerPoint attachments
>> Seehttp://www.gnu.org/philosophy/no-word-attachments.html
>> ==========================================================
>
> I am running on a Dell XPS Laptop using Windows XT and the code seems
> to work -- nothing much happens when I move the viewpoint slider --
> the display moves slightly -- nothing more.
>
> Gary
>
>


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