Hi Folks,

As suggested, I wrote a transformation macro to align a pigment using 
three points. Turned out to be very simple, the idea based on the 
Point_At_Trans() macro.

It also uses radiosity and the Skylight dome generator by Philippe 
Debar. I do need to make a modification of this to write the mesh out as 
an include and just read it back in for each frame, rather than 
rebuilding it each time :-/

Hope you like this one.

Bye for now,
	Mike Andrews.

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Attachments:
Download 'bball.avi.dat' (313 KB)

Michael Andrews wrote:
> Hope you like this one.

Looks so much better with a Texture on the ball - reminds me of the old
Amiga ball demo


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Rick

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"Michael Andrews" <m.c### [at] readingacuk> wrote in message
news:3e54a341@news.povray.org...
> Hi Folks,
>
> As suggested, I wrote a transformation macro to align a pigment using
> three points. Turned out to be very simple, the idea based on the
> Point_At_Trans() macro.
>
> It also uses radiosity and the Skylight dome generator by Philippe
> Debar. I do need to make a modification of this to write the mesh out as
> an include and just read it back in for each frame, rather than
> rebuilding it each time :-/
>
> Hope you like this one.

I do.. I do! Top marks.. 100%. Really great work there. What's the sim time per frame?

All the best,

Andy Cocker

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I've got an include which could be suited for the job:
the IO-Macros, which you can find on my homepage.
They'll at least write an array (any 5-dimensional) to
disk and may load it. But they may not be what you want,
still you might want to have a look at those for input-output
"examples".

Regards,Tim


--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

> Hi Folks,
>
> As suggested, I wrote a transformation macro to align a pigment using
> three points. Turned out to be very simple, the idea based on the
> Point_At_Trans() macro.
>
> It also uses radiosity and the Skylight dome generator by Philippe
> Debar. I do need to make a modification of this to write the mesh out as
> an include and just read it back in for each frame, rather than
> rebuilding it each time :-/
>
> Hope you like this one.
>
> Bye for now,
> Mike Andrews.
>

Post a reply to this message

Rick [Kitty5] wrote:
> Looks so much better with a Texture on the ball - reminds me of the old
> Amiga ball demo

Hi Rick,

Yes, the texturing adds a lot. I surprised myself with how easy the 
orientation macro was to write:

#macro Three_Point_Trans(T1a, T1b, T1c, T2a, T2b, T2c)
   transform {
     #local Y = vnormalize(T1b - T1a);
     #local X = vnormalize(T1c - T1a);
     #local Z = vnormalize(vcross(X, Y));
     #local X = vcross(Z, Y);
     #local T = Shear_Trans(X, Y, Z)
     translate -T1a
     transform { T inverse }
     #local Y = vnormalize(T2b - T2a);
     #local X = vnormalize(T2c - T2a);
     #local Z = vnormalize(vcross(X, Y));
     #local X = vcross(Z, Y);
     Shear_Trans(X, Y, Z)
     translate T2a
   }
#end

The three points a,b,c define a triangle; a is the origin, b-a is the 
primary orientation and abc gives a secondary orientation plane. The two 
orientation axes b-a and c-a do not have to be orthogonal, just 
independant so vcross(b-a,c-a) doesn't return a zero length vector.

So Three_Point_Trans(0,y,x, P0,P1,P2) gives a transform from the origin 
to P0, aligns y with P1-P0 and puts the (x,y) plane in the plane of the 
(P0,P1,P2) triangle.

I never actually had an Amiga; Atari 400, Acorn Electron, BBC B, various 
PC types ... I wrote my first (spheres only) raytracer on my Electron, 
16 colour error-diffusion dithered screen output only :-) The hardware 
and software have improved immeasurably, it's a shame I still can't 
produce anything artistic :-(

Bye for now,
	Mike Andrews.

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Hi Andrew,

Andrew Cocker wrote:
> I do.. I do! Top marks.. 100%. Really great work there. 

Thanks :-)

>What's the sim time per frame?

Quite quick; parsing time averaged 23.5 seconds per frame, but most of 
that was building the skylight mesh. I didn't notice what the actual sim 
time was.

The sim has 151 masses, 594 connections, 296 faces and 2500 steps.

Bye for now,
	Mike Andrews.

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Hi Tim,

Tim Nikias wrote:
> I've got an include which could be suited for the job:
> the IO-Macros, which you can find on my homepage.
> They'll at least write an array (any 5-dimensional) to
> disk and may load it. But they may not be what you want,
> still you might want to have a look at those for input-output
> "examples".

Not really what I want, but thanks for the thought. For reusing things 
like meshes in an animation I usually write the complete mesh to a file 
on the first frame and then just #include "hull.msh" or whatever on 
subsequent frames. It only takes a couple more #writes() and I don't 
have to worry about parsing anything back in - just let PoV do the work 
for me :-)

Bye for now,
	Mike Andrews.

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Michael Andrews wrote:
> 
> Hi Folks,
> 
> As suggested, I wrote a transformation macro to align a pigment using
> three points. Turned out to be very simple, the idea based on the
> Point_At_Trans() macro.

Nice. Is the mass distribution between rim masses and central mass correct
so you get a correct moment of inertia?  Maybe you should also try making
one side of the ball heavier. I think this would look interesting.  

Christoph

-- 
POV-Ray tutorials, include files, Sim-POV,
HCR-Edit and more: http://www.tu-bs.de/~y0013390/
Last updated 31 Dec. 2002 _____./\/^>_*_<^\/\.______

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Michael Andrews <m.c### [at] readingacuk> wrote in
news:3e54d2d5$1@news.povray.org: 

...
>I surprised myself with how easy the 
> orientation macro was to write:
> 
> #macro Three_Point_Trans(T1a, T1b, T1c, T2a, T2b, T2c)
>    transform {
>      #local Y = vnormalize(T1b - T1a);
>      #local X = vnormalize(T1c - T1a);
>      #local Z = vnormalize(vcross(X, Y));
>      #local X = vcross(Z, Y);
>      #local T = Shear_Trans(X, Y, Z)
>      translate -T1a
>      transform { T inverse }
>      #local Y = vnormalize(T2b - T2a);
>      #local X = vnormalize(T2c - T2a);
>      #local Z = vnormalize(vcross(X, Y));
>      #local X = vcross(Z, Y);
>      Shear_Trans(X, Y, Z)
>      translate T2a
>    }
> #end
> 
> The three points a,b,c define a triangle; a is the origin, b-a is
> the primary orientation and abc gives a secondary orientation plane.
> The two orientation axes b-a and c-a do not have to be orthogonal,
> just independant so vcross(b-a,c-a) doesn't return a zero length
> vector. 
> 
> So Three_Point_Trans(0,y,x, P0,P1,P2) gives a transform from the
> origin to P0, aligns y with P1-P0 and puts the (x,y) plane in the
> plane of the (P0,P1,P2) triangle.
...

Here is a slightly modified version of that macro:


#macro ThreePoint_Trans(pA1, pB1, pC1, pA2, pB2, pC2)

  #local vY1 = vnormalize(pB1 - pA1);
  #local vZ1 = vnormalize(vcross(pC1 - pA1, vY1));
  #local vX1 = vcross(vZ1, vY1);
  #local T1 = transform { Matrix_Trans(vX1, vY1, vZ1, pA1) inverse }
  #local vY2 = vnormalize(pB2 - pA2);
  #local vZ2 = vnormalize(vcross(pC2 - pA2, vY2));
  #local vX2 = vcross(vZ2, vY2);
  #local T2 = transform { Matrix_Trans(vX2, vY2, vZ2, pA2) }

  transform { T1 T2 }

#end // macro ThreePoint_Trans
 

Tor Olav

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Hi Tor Olav,

Tor Olav Kristensen wrote:
> Here is a slightly modified version of that macro:
> 
> 
> #macro ThreePoint_Trans(pA1, pB1, pC1, pA2, pB2, pC2)
> 
>   #local vY1 = vnormalize(pB1 - pA1);
>   #local vZ1 = vnormalize(vcross(pC1 - pA1, vY1));
>   #local vX1 = vcross(vZ1, vY1);
>   #local T1 = transform { Matrix_Trans(vX1, vY1, vZ1, pA1) inverse }
>   #local vY2 = vnormalize(pB2 - pA2);
>   #local vZ2 = vnormalize(vcross(pC2 - pA2, vY2));
>   #local vX2 = vcross(vZ2, vY2);
>   #local T2 = transform { Matrix_Trans(vX2, vY2, vZ2, pA2) }
> 
>   transform { T1 T2 }
> 
> #end // macro ThreePoint_Trans
>  
> 
> Tor Olav

Nice. I used the Shear_Trans() macro because that's what the 
Point_At_Trans() macro used, I didn't think to use the Matrix_Trans() to 
do the shear and translate in one go. Kudos to you :-)

Bye for now,
	Mike Andrews.

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