[Kst] getData flexibility

[Eli Fidler]

George and I have discussed this issue some more. I think that we need to 
change the internals of Kst, particularly RVector. I think that instead of 
containing a range of samples from frame 0 to n, we should be able to store a 
set of frame ranges.

Some situations where this is useful:
1. The cache contains frames 10-20 and 100-500 of a field. The server is 
unreachable. Kst can use the stored frames from the cache and add the other 
frames once the server is reachable. Without frame ranges, I would have to 
either say the datasource is empty, allow the user to use the first range 
only or allow the user to retrieve all the frames but 0-9 and 21-99 will be 
filled with NaNs. None of these solutions are very good.

2. Progressive loading. The user could retrieve frames 0-end skip 10, then 
1-end skip 10, then 2-end skip 10... The RVector would know which frames are 
missing and still need to be retrieved.

3. I think frame ranges is a better representation of holes in the data than 
NaNs. It could be useful to visualize missing frame ranges by shading in the 
gui. Frame ranges would work for masking as well.

4. We could remove the hack in the piolib datasource which moves all the 
vectors to frame 0. I don't know exactly what the dirfile datasource does 
with data that doesn't begin at frame 0 as I don't have such a dirfile, but a 
similar hack likely exists.

I have a class in NAD which stores sets of frame ranges (QPair<uint32_t, 
uint32_t>'s actually). It allows you to add ranges, intersect ranges, skip, 
etc. I think it could be used in Kst with some modifications. The header file 
is attached.

I'm interested in people's thoughts on this idea.

Eli

On Tuesday 02 May 2006 18:08, Eli Fidler wrote:
> I'm in the process of writing the new NAD KstDataSource with uses the local
> cache. I've run into a case of getData() where the current interface seems
> insufficient.
>
> When using the NAD cache, I may have frames 1 to 50 of a particular field
> in the cache. If the NAD server connection is unavailable, what should I do
> if the user requests frames 1 to 100? What about 1 to 50?
>
> I assume I should just give them the data in the second case and pretend
> everything is fine. In the first case, should I return partial data? no
> data? something else?
>
> What if I have part of the data, but it's not the first part?
>
> The problem stems from the fact that I can only return -1 for any error, so
> I can't signal a partial success very easily.
>
> Eli
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