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Currently my problem is with the linear gradients when a matrix operation 
is applied on them.


The linear gradient use a vector v = (x1, y1) - (x2, y2) to indicate 
his direction and length.


grad-pen is defined like this:  [grad-pen linear normal xy 0 len 
angle [... stop colors]]

And i calculate his values with:

- xy = (x1,y1)
- len =  length of the vector v 
- the angle of the vector v


When a matrix is associated with the gradient, i multiply the coordinates 
of the vector v by the matrix before calculating the other values.
It's working well when the gradient is vertical or horizontal.

But when the gradient is inclined , the matrix multiplication give 
a wrong vector and i don't know why.