Slow isDone()

[Boudewijn Rempt]

I've got the bumpmap filter working, and now I'm optimizing it. One point 
where the filter took a lot of time was calling isDone() on the iterator,
compared to using a counter:

isDone():

krita (filters): Filter activated: Bumpmap
krita: Mapping took: 35
krita: Mapping took: 1939
krita (filters): Filter activated: Bumpmap
krita: Mapping took: 38
krita: Mapping took: 2047
krita (filters): Filter activated: Bumpmap
krita: Mapping took: 40
krita: Mapping took: 1900

counter:

krita (filters): Filter activated: Bumpmap
krita: Mapping took: 32
krita: Mapping took: 1134
krita (filters): Filter activated: Bumpmap
krita: Mapping took: 35
krita: Mapping took: 1744
krita (filters): Filter activated: Bumpmap
krita: Mapping took: 32
krita: Mapping took: 1194
krita (filters): Filter activated: Bumpmap
krita: Mapping took: 34
krita: Mapping took: 1761


The small number is for the preview: the larger number for a 1000x1000 image. 
There's some variation, of course, because I just use QTime.elapsed, but the 
pattern is clear: isDone() is always slower.

isDone() is not just a function call; except in the rect iterator it's 
actually a computation.

In the light if this I wonder whether we shouldn't stop using isDone(). After 
all, paint devices have no bounds, reads and writes are always valid, and we 
know the extent to which we want to read beforehand because we give it as a 
parameter to the create functions.
-- 
Boudewijn Rempt 
http://www.valdyas.org/fading/index.cgi
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