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OK, can someone tell me why this generates a parse error:
#declare Spline = spline {cubic_spline
-2/13, <-1,0,0>
-1/13, <0,0,0>
0, <1,0,0>
1/13, <5,0,0>
2/13, <8,0,0>
}
While this doesn't:
#declare Spline = spline {cubic_spline
-2/13, <-1,0,0>
(-1/13), <0,0,0>
0, <1,0,0>
1/13, <5,0,0>
2/13, <8,0,0>
}
The only difference between these two bits of code is the brackets
around -1/13.
I'm hopelessly confused as to why the brackets are necessary on that one
line, and that one line alone.
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In article <3c4990b9$1@news.povray.org>,
"Andrew" <ast### [at] hotmail com> wrote:
> OK, can someone tell me why this generates a parse error:
>
> #declare Spline = spline {cubic_spline
> -2/13, <-1,0,0>
> -1/13, <0,0,0>
> 0, <1,0,0>
> 1/13, <5,0,0>
> 2/13, <8,0,0>
> }
You don't have commas separating the items. POV-Ray doesn't care about
spaces or separate lines, it sees:
-2/13, <-1,0,0>
-1/13, <0,0,0>
as:
-2/13, <-1,0,0> - 1/13, <0,0,0>
When you add in the parentheses, it sees:
-2/13, <-1,0,0> (-1/13), <0,0,0>
and can figure out that the "-1/13" is a separate value.
--
--
Christopher James Huff <chr### [at] maccom>
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Aha! Thank you. I thought it would be something really obvious, and I
had wondered why commas weren't necessary. I guess I shall simply use
commas at all times now.
> You don't have commas separating the items. POV-Ray doesn't care about
> spaces or separate lines, it sees:
> -2/13, <-1,0,0>
> -1/13, <0,0,0>
> as:
> -2/13, <-1,0,0> - 1/13, <0,0,0>
>
> When you add in the parentheses, it sees:
> -2/13, <-1,0,0> (-1/13), <0,0,0>
> and can figure out that the "-1/13" is a separate value.
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Why are those commas optional anyway?
- Slime
[ http://www.slimeland.com/ ]
[ http://www.slimeland.com/images/ ]
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In article <3c49da50$1@news.povray.org>, "Slime" <noo### [at] hotmailcom>
wrote:
> Why are those commas optional anyway?
Backwards compatibility. The same code is used to parse all commas, and
that code was written to support the old <xVal yVal zVal> vector syntax,
so it tries to accept blank spaces. Sometimes it accepts them when it
shouldn't, but it has no way to tell...
--
--
Christopher James Huff <chr### [at] maccom>
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Andrew <ast### [at] hotmailcom> wrote:
: had wondered why commas weren't necessary.
The main reason is backwards compatibility, but there are other really good
reasons as well.
For example, suppose that you wanted to make the spline points inside a
loop. You could do something like this:
spline
{ cubic_spline
#declare Ind = 0;
#while(Ind < 10)
Ind, <Ind, Ind*Ind, 0>
#declare Ind = Ind+1;
#end
}
Now suppose that the commas were mandatory. That wouldn't work anymore.
It won't work either if you add a comma after the vector.
I'll let it as an exercise how complicated that would need to be done if
commas were mandatory.
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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In article <3c49df0d@news.povray.org>, Warp <war### [at] tagpovrayorg>
wrote:
> I'll let it as an exercise how complicated that would need to be done if
> commas were mandatory.
Not very. I always do it anyway, for possible forwards compatability in
case a future version makes them required.
spline {cubic_spline
#declare Ind = 0;
#while(Ind < 9)
Ind, <Ind, Ind*Ind, 0>
#declare Ind = Ind + 1;
#end
Ind, <Ind, Ind*Ind, 0>
}
--
--
Christopher James Huff <chr### [at] maccom>
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"Warp" <war### [at] tagpovrayorg> wrote:
> Now suppose that the commas were mandatory. That wouldn't work anymore.
> It won't work either if you add a comma after the vector.
> I'll let it as an exercise how complicated that would need to be done if
> commas were mandatory.
Only one line more, if the following parses ...
spline
{ cubic_spline
0, 0
#declare Ind = 1;
#while(Ind < 10)
,Ind, <Ind, Ind*Ind, 0>
#declare Ind = Ind+1;
#end
}
OK .. I(We all) know, what you mean, but probably this example was too simple
...
Question: How far back do we need Backward-compatibility ?
Commas are standard at least since 3.0, so I think somewhere should be a
hard-cut ...
_IF_ all the suggestions for the (somewhere in the far future) POV4 will
come true, we
will have a complete(?) different SDL, with hardly any way for
backward-compatibility ...
--
[Talking about cardriving]
"People are opstacles?
Oh...I always treat them as bonus points..." [Ian Burgmyer in p.o-t]
// Jan Walzer <jan### [at] lzernet>
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Christopher James Huff <chr### [at] maccom> wrote:
: Not very. I always do it anyway, for possible forwards compatability in
: case a future version makes them required.
If a future version makes commas mandatory, that would be a huge step
*backwards* in versatility.
(Unless a #-command can replace a comma.)
--
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}// - Warp -
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In article <3c49ec58@news.povray.org>, Warp <war### [at] tagpovrayorg>
wrote:
> If a future version makes commas mandatory, that would be a huge step
> *backwards* in versatility.
How?
--
--
Christopher James Huff <chr### [at] maccom>
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