#371 Merge area command shows weird behaviour

[Matthias Kühlewein]

Trying to merge areas that don't overlap leads to strange effects, use the map (MergeAreaSample) attached e.g.
- select the both rightmost areas: trying to merge leads to changing the symbol type for one area
- select the both rightmost areas and the one at the top: trying to merge leads to deleting one area and to changing the symbol type for one of the remaining ones
- select all areas: all but two are deleted and one of the 'surviving' areas changes its type to that of the other remaining one

Even if two areas of the same type overlap, selecting those two and another one leads to similar effects.

If three areas of the same type partially overlap (see MergeAreaSample2), then only two of them are merged and one is deleted.

[Kai Pastor]

The result of merging will always have the symbol of the first selected object.

Since the last boolean operation modification, operations on two objects work much better now. But more than two objects is a different story...

[Thomas Schöps]

If I remember correctly, before the modifications the tool worked by finding all subsets of area objects with the same symbol in the object selection, and applying the merge to every subset separately. In particular, this means that objects with different symbols were not merged. I think that this is useful: it prevents "merging in" accidentally selected areas and doesn't unexpectedly change symbols. If a user really wants to merge areas with different symbols, it's easy to use the symbol conversion tool before.

[Kai Pastor]

I now tested 0.5.3/wine, and it's behaviour is not as perfect as the previous comment indicates:

• Merging is disabled as long as you don't have at least two objects of the same symbol (okay).

• Merging is indeed done independently for each group of objects of the same symbol (okay).

• However, all resulting objects will have the symbol of the first selected original object, except if there is only a single original object of a symbol. (This is weird.)

So the current implementation is merging thoroughly, at least:-)

I agree that grouping objects by original symbols - and keeping these symbols - is a good proposal.

[Kai Pastor]

The unify-area tool now handles each group of objects sharing the same symbol independently. Other than in Mapper 0.5, the symbol remains unchanged. Note that this behaviour is diferent from the other boolean tools which use the first selected object as "primary object".

Only objects with area symbolks are unified this way. Closed paths (e.g. separate border line symbols) are ignored.