POV-Ray : Newsgroups : povray.beta-test : <1, 0, 0> + 1*t : Re: <1, 0, 0> + 1*t Server Time
17 Aug 2022 00:31:43 EDT (-0400)
  Re: <1, 0, 0> + 1*t  
From: Mike Williams
Date: 21 Jan 2002 01:48:09
Message: <ZgqRnDAol7S8EwIR@econym.demon.co.uk>
Wasn't it mm who wrote:
>I don't know if it is a bug or intended, but it caused me some loss of time
>: the <1, 0, 0> + 0.5*t  yields <1, 0, 0, 0> and not <1, 0, 0, 0.5> as
>expected (by me!). (This happens whatever the number at the place of 0.5)
>Additions <1, 0, 0> + t, <1, 0, 0> + t*1, or 1*t + <1, 0, 0> yield <1, 0, 0,
>1>!
>
>#macro V4Show(S, V)
>#debug concat(S, ": ", str(V.x,6,2), ", ", str(V.y,6,2), ", ",str(V.z,6,2),
>", ",str(V.t,6,2), "\n")
>#end
>
>#declare vvv = <1, 0, 0> +1*t;
>V4Show("vvv ",vvv)


The documentation states that "t" is defined as

 #declare t = <0, 0, 0, 1>;

But that's a long way from the place where we learned that the order of
the vector components is "rgbft". The fourth vector is "filter", not
"transmit".

V.t extracts the fifth component, not the fourth.


I reckon things would make more sense if "t" where defined (and
documented) to be <0,0,0,0,1> and "f" were defined to be <0,0,0,1,0>,
but the current code works exactly as documented, so it's not really a
bug.

-- 
Mike Williams
Gentleman of Leisure


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