"clipka" <nomail@nomail> wrote in message 
news:web.49afac96ed80e874f567c3de0@news.povray.org...
> Um... unfortunately, rotation stuff is quite complex, and I know neither 
> whether
> you got the docs right

No, no...you are correct, I actually *do* have no idea what I'm talking 
about. :-p
I tend to learn best by undertaking difficult tasks with basically no idea 
what I am doing.
I know, I'm weird.. :-D

>nor whether I get you right :}

This is likely, as I am worse than horrible at explaining things that I 
happen to be attempting, as I am sure you have realized by now.  :-)

>
> First off, vrotate(A,B) does the same thing to vector A that an "object 
> { O
> rotate B }" does to the whole object O; i.e., B does not specify the axis 
> to
> rotate about, but rather a set of three consecutive rotations about the X, 
> Y
> and Z axes respectively.

I found this out by dicking around these last few hours.

> For that reason, computing the dot product of A and B makes absolutely no 
> sense.
>
> Speaking of the VRotation macro and the perpendicular axis, the thing you 
> should
> input to - say - VRotation(A,B,C) - as C is c*VCross(A,B), where c is an
> arbitrary float constant, of which only the size matters.

Ok, so I wasn't too awfully far from target there at least.

> Actually, to my knowledge the only added value of VRotation over VAngle is 
> that
> while VAngle just gives you the angle between two vectors, VRotation will 
> add
> some direction information to this angle.

This is potentially useful.

> Maybe the best thing is you tell us what you actually want to do; vector 
> stuff
> involving rotations is quite a complex topic (as you can probably see from 
> the
> number of macros related to it).

Ok.
I'm using the following macro (ye olde snowmacro core) to output relevant 
vectors along with the surface normal:

#macro 
GDSX_VectTestN(Array,normArray,ctr,vectorArray,testVector,testObject,Normal)
 #local vectorA = min_extent(testObject);
 #local vectorB = max_extent(testObject);
 #local i=0;
 #while (i<ctr)
  #if (((vectorArray[i].x <= vectorB.x) & (vectorArray[i].x >= vectorA.x)) & 
((vectorArray[i].y <= vectorB.y) & (vectorArray[i].y >= vectorA.y)) & 
((vectorArray[i].z <= vectorB.z) & (vectorArray[i].z >= vectorA.z)))
   #if (inside(testObject,vectorArray[i]))
    #declare Array[i] = trace(testObject,vectorArray[i],testVector,Normal);
    #declare normArray[i] = Normal;
   #end
  #end
 #set i=i+1;
 #end
#end

This works well, and I've tested the output with cyls, which give the effect 
that I want, with the obvious exception that cyls make *terrible* moss. 
Since I'm dealing with a moss object generated from a macro that 
approximates Campylopus sp., which is obviously more complicated than a cyl, 
I need to find a meaningful way to rotate the individual models according to 
the surface normal to acheive any kind of meaningful effect.

Right now I am stuck with the attached image, and I know you guys are just 
about sick of that damned torus, but it renders fast and has a hole, so is 
useful for testing trace based effects.
I also would like to use some kind of rotation within the actual moss object 
macro every so often, as real moss isn't y+ straight (but the base of one 
object must remain stationary while the top moves, I think NewTop = 
vrotate(CylTop-CylBot,<30,0,0>)+CylBot; as proposed by Chris B might get 
that at least in part, but requires the solution to the other problem to 
use).

Thanks!
ian

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