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Le 17-11-07 à 14:32, Kenneth a écrit :
> I'm having a subtle problem that I can't pin down, when trying to use
> logical-OR statements inside of #case directives. I'm using the strcmp()
> function to compare various strings, plus OR blocks separating those strcmp()
> comparisons inside of each #case. Posting my problematic scene code isn't
> practical here (it involves lots of image_maps), but I came up with a simplified
> test. I'm hoping to glean some insights into these interactions, from more
> astute newsgroup observers ;-)
>
> There are four things involved: strings, #switch/#case, the strcmp() function,
> and OR.
>
> Here's the test code, before I go into the details. Note that IMG_TYPE and AA
> exactly match. The problem is that #switch is falling through to the #else
> clause, when it should not do so (because IMG_TYPE and AA *are* the same.) If
> the #case clause is successful, you'll see a GREEN box; otherwise, a
> crosshatched box. Comment-out the two OR lines for a successful test.
> --------------------
> #version 3.71; // or 3.7
>
> global_settings{assumed_gamma 1.0 max_trace_level 5}
> default{finish{ambient 0 emission 1 diffuse 0}}
>
> camera {
> perspective
> location <.5, .5, -1.5>
> look_at <.5, .5, 0>
> }
>
> #declare IMG_TYPE = "jpg"
> #local AA = "jpg"
> #local BB = "png"
> #local CC = "tiff"
>
> box{0,<1,1,0>
> no_shadow
> pigment{
> #switch(1000)
> #case(
> // INDIVIDUALLY, these all work the way they are supposed to-- but not
> // all three at once. The OR's are causing some kind of problem, and
> // the result always fall through to the #else clause.
> (strcmp(IMG_TYPE,AA) + 1000)
> | (strcmp(IMG_TYPE,BB) + 1000)
> | (strcmp(IMG_TYPE,CC) + 1000)
> )
> srgb <0,1,0> // GREEN square
> #debug "\nAt least ONE of the #case clauses is valid.\n\n\n\n"
> #break
> #else
> // A cross-hatch warning image...
> average
> pigment_map{
> [1 gradient x+y
> frequency 6
> color_map{
> [.25 srgb <1,0,0>]
> [.25 srgb 0]
> }
> ]
> [1 gradient x-y
> frequency 6
> color_map{
> [.25 srgb <1,0,0>]
> [.25 srgb 0]
> }
> ]
> }
> #debug "\nNO #case clause is valid.\n\n"
> #end // of #switch
> } // end of pigment
> }
> -----------------------
>
> I assume that a #case clause can USE logical operators like ORs??
>
> What DOES work is to *remove* all of the OR blocks--using just ONE
> strcmp() + 1000 in the #case (any one of the three). That results in correct
> #switch behavior (either a 'go' of 'no go'.) That's not what I want, of course,
> as I need all three in the #case statement. But is it possible that OR is not
> the correct logical operator to use? One *guess* I have is that #case is
> 'reading' the strcmp()-plus-OR blocks left to right-- and finally comes to
> strcmp(IMG_TYPE,CC) + 1000, the result of which does NOT 'match'
> #switch(1000) ... possibly causing the fall-through to the #else clause(?)
>
> My understanding of #switch is that ANY value can be used; it doesn't
> specifically need just TRUE/FALSE of 1/0, just so long as a particular #case
> result matches it. But I don't really know its hidden operation. BTW, I didn't
> use 'TRUE' in the #switch() because, when strcmp() finds two strings that
> *match*, its numerical output is zero-- which should be a logical 'false' in a
> TRUE/FALSE clause, not 'true.' (AFAIU!)
>
> Perhaps I shouldn't be using strcmp() at all. It *is* a rather complex beast--
> its numerical output depends on where the various strings fall into the 'ASCII
> collating sequence.' (I had to re-read the docs to try and understand this,
> along with running some experiments.) My use of +1000 in the #switch clause
> (and in the #case arguments) was to try and avoid such problems, as 1000 is way
> outside of the ASCII numbering sequence. But no matter *what* numerical value I
> use-- while also using the ORs-- the #else clause is always invoked.
>
> And in my real scene, I'm finding that the OR clauses *sometimes* need the added
> parentheses around the various strcmp() + 1000 statements -- but that
> seems to work inconsistently as well :-/
>
>
>
>
The OR operator is a binary operator. It can only return a result of
zero or one. Any input <> zero result in a true/on/1 result, and zero
returns flase/off/0.
You check for a value of 1000 that can NEVER appen.
You can use your OR statement inside parantesis, THEN add 1000 or
multiply by 1000.
You can have 3 #case() statements without ending #greak. That way, the
first will fall through the next two, and the second falls through the last.
You can use "on" in your #switch statement.
You can replace your #switch by an #if statement.
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