Am 10.07.2016 um 09:00 schrieb Thomas de Groot:
> On 9-7-2016 13:42, clipka wrote:
>> Am 09.07.2016 um 13:17 schrieb Thomas de Groot:
>>> On 9-7-2016 12:38, clipka wrote:
>>>> Am 09.07.2016 um 08:52 schrieb Thomas de Groot:
>>>>> On 7-7-2016 16:02, Bald Eagle wrote:
>>>>>> I see:
>>>>>> #declare WriteStrands = off; //set to 'on' for the first pass.
>>>>>>
>>>>>> Isn't there a way to just check if the file exists, and if not,
>>>>>> create
>>>>>> it?
>>>>>> I looked - but it's not clear that this is possible.
>>>>>> Seemed like a useful and desirable feature to be added, if that's the
>>>>>> case.
>>>>>>
>>>>>
>>>>> In fact, there is a simple reason why I did not use the file_exists(S)
>>>>> function, now that I think about it. It is that you may want to test
>>>>> different settings before choosing the final ones (at least that is
>>>>> how
>>>>> I work) and so - except for the very first time - there is always a
>>>>> file
>>>>> present.
>>>>
>>>> You could use something like:
>>>>
>>>>     #declare WriteStrands = off; // set to 'on' to force re-writing
>>>>     ...
>>>>     #if (!file_exists(...)) #declare WriteStrands = on; #end
>>>>
>>>
>>> But, that would always set it to on, even when you want it to be off, or
>>> do I misunderstand this?
>>
>> It would always set it to on _if_ the file does not already exist, so
>> you don't need to manually set it to on for the first run.
>>
>> Of course if there are any use cases where you might want to have _no_
>> file at all, then this is of no use.
> 
> I think you misunderstand my use of the on/off switch.

Not at all. But you apparently misunderstand my use of `file_exists()` ;)

> The writing away
> of data is only meant as time saving later on when reading the data
> (always faster than having to do the complete calculations for each
> run). So, the switching off of the writing section (once you are
> satisfied with the written data) is essential. A file_exist switch can
> only make sense to check the existence of a file in the "Read" section
> of the macro.

No, the `file_exists()` test makes perfect sense before the file
generation. It's pretty simple:

- You use `#declare WriteStrands = on;` while experimenting, forcing a
(re-)write on every run.

- You use `#declare WriteStrands = off;` once you're ok, suppressing a
re-write.

- In case the file does not yet exist, the `#if (!file_exists(...))
#declare WriteStrands = on; #end` overrides your choice and forces a
write, thus making sure that the finished scene can be rendered as-is,
with no tampering necessary even if the data file happens to be missing
for some reason.

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