On 07/10/2016 11:50 AM, clipka wrote:
> Am 10.07.2016 um 17:30 schrieb William F Pokorny:
>
>> OK. If the optionality is what we are trying to indicate, I think we
>> probably want something like :
>>
>> COLOR_VECTOR:
>>       [rgb] float            | (promoted to 3 value vector)
>>       [rg0] <2 Term Vector>  |
>>       [rgb] <3_Term_Vector>  |
>>       [rgbf] <4_Term_Vector> |
>>       rgbt <4_Term_Vector>   |
>>       [ rgbft ] <5_Term_Vector> |
>>       srgb <3_Term_Vector>   |
>>       srgbf <4_Term_Vector>  |
>>       srgbt <4_Term_Vector>  |
>>       srgbft <5_Term_Vector>
>
> Since floats and less-than-5-term vectors are automatically promoted to
> 5-term vectors this is not necessary. To the contrary, what you suggest
> might be misinterpreted to imply that e.g. `rgbft <4_Term_Vector>` would
> be invalid, when in fact it is perfectly legal.
>
> Also, there is no `rg0` keyword, so that's plain nonsense right there.
>
(Indeed. I'm about half nonsensical in any given moment. ;-) See my own, 
earlier correction to rg0)

The block under discussion is in the section:

http://wiki.povray.org/content?title=Reference:Color_Expressions

where we describe how a user can specify color as in:

pigment { color .... }

In this context it seems to me we care not that a 5 term vector is 
otherwise treated by POV-Ray as a color vector by default, but whether 
we need to specify the rgb... whatever string in the color 
specification. In the latter context I think what I have written is what 
happens. All these are today valid ways to specify color:

color 1           // We get white
color <1,1>       // We get yellow
color <1,1,1>     // White
color <1,1,1,1>   // Clear by filter
color <1,1,1,1,1> // Again clear

Bill P.

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