"Samuel B." <stb### [at] hotmailcom> wrote:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> > 3) so it appears (to me) that the texture does not follow the object
> > rotation. Why this is is a mystery to me and it is the first time I
> > witness such behaviour indeed.
>
> Regarding your third bullet point... The texture not following the object's
> rotation is an issue I predicted, but was unsure if it would manifest or not. My
> guess is that the slope inputs (x, y, z) need to be rotated independently of the
> object [...]

(To everyone: I'm sorry for not replying to everything right now.)

As you've seen, rotating an object using a slope pattern doesn't give the result
one would hope for. Whether the rotation is placed before or after the triplanar
pattern matters a /bit/, but not enough: in either case the result will be
wrong. The answer seems to be to rotate the slope vectors /independently/ of the
object.

In the attached image, the left object is rotated in a naive manner. The right
object uses a new macro that rotates the slope vectors in tandem with the
object. It can be a hassle to do it this way, but it would appear that if you
wish to rotate your object it's what you have to put up with ;)

Here's the scene code:

/*
 triplanar-debug.pov

 2024 stb

 +fn +f +a0.3 +am2 +r2 +w1024 +h512
*/


#version 3.7;

global_settings{assumed_gamma 1.0}

camera{
 orthographic
 right x*2 up y
 location <0, 5, -10>
 look_at 0
 angle 33
}

// sunlight
#if(true)
 light_source{
  <1, .5, 0>*1e5, srgb <1.5, 1.4, 1.3>
  shadowless
 }
#end

// starry background
#if(true)
 background{rgb .5}
#end

// input image for triplanar color and normal
#declare PImg =
 pigment{
  image_map{
   png "craters.png"
   interpolate 2
  }
  scale 2
 }

#declare ObjRotate = <0, 37, 0>;

/*
 Triplanar macro
  Pigment: a pigment oriented in the z-direction
  Sharpness: a value between 0 and 1
  Rotate: the object's rotation
*/
#macro TriplanarR(Pigment, Sharpness, Rotate)
 pigment_pattern{
  slope vrotate(x, Rotate)
  triangle_wave
 }
 pigment_map{
  [0+.5*Sharpness Pigment rotate y*90]
  [1-.5*Sharpness
   pigment_pattern{
    slope vrotate(y, Rotate)
    triangle_wave
   }
   pigment_map{
    [0+.5*Sharpness Pigment rotate x*90]
    [1-.5*Sharpness Pigment rotate z*165]
   }
  ]
 }
#end

// don't use this if you want to rotate your object
#macro Triplanar(Pigment, Sharpness)
 pigment_pattern{
  slope x
  triangle_wave
 }
 pigment_map{
  [0+.5*Sharpness Pigment rotate y*90]
  [1-.5*Sharpness
   pigment_pattern{
    slope y
    triangle_wave
   }
   pigment_map{
    [0+.5*Sharpness Pigment rotate x*90]
    [1-.5*Sharpness Pigment rotate z*165]
   }
  ]
 }
#end

// object on left (naive rotation)
superellipsoid{
 <.2, .2>

 texture{
  pigment{pigment_pattern{Triplanar(PImg, .5)}}
  normal{
   pigment_pattern{Triplanar(PImg, .5)}
   poly_wave .5
   bump_size .75
   accuracy .01
  }
 }

 rotate ObjRotate

 translate -x*1.5
}

// object on right (corrected rotation)
superellipsoid{
 <.2, .2>

 texture{
  pigment{pigment_pattern{TriplanarR(PImg, .5, ObjRotate)}}
  normal{
   pigment_pattern{TriplanarR(PImg, .5, ObjRotate)}
   poly_wave .5
   bump_size .75
   accuracy .01
  }
 }

 rotate ObjRotate

 translate x*1.5
}


Sam

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