[eigen] Eigen2 in Krita

[jacob@xxxxxxxxxxxxxxx]

Hi,

Just letting you know that Eigen 2 is now being used quite a lot in  
Krita. I just replaced their old KisVector2D class by a typedef around  
essentially Vector2d (qreal instead of double to be precise, but  
that's double in most cases). Their code lends itself very well to  
this porting, for example they have a lot of
  center = (p1 + p2) / 2;
which is benefiting a lot from expression templates (only one vector  
traversal instead of 3). Another nice thing is that Vector2d is of  
course nice for vectorization. One of the places where this should  
bring large performance improvements is in the Bezier curves.

There are other usages, for example Cyrille wrote a perspective  
transformation tool a while ago, using a 9x9 LU solver which is now  
provided by Eigen.

The most useful thing in the future would be a complete Sparse module  
with some features such as least squares (Ben and Cyrille could  
refresh us on what exactly is needed). That would allow to remove the  
GMM dependency, and hopefully to improve performance. Perhaps for  
KOffice 2.1...

Cheers,
Benoit

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