[Gegl-developer] API change for samplers to pass inverse Jacobian data to samplers

[Nicolas Robidoux]

Adam Turcotte writes:
> In addition, I will need to expand the OpAffine struct to include an
> additional GeglMatrix3 (call it matrix_inverse or inverse_jacobian?)
> to store this data.

GeglMatrix3?  Is this a 3x3 matrix type?

(Ignore the following if it is not.)

Maybe the matrix created by the create_matrix () method is not really
the "plain Jacobian matrix" even for affine transformations.

I understand that there are convenient representations of common image
transforms in terms of 3x3 matrices, but I wonder if using a 3x3 to
store either the Jacobian or its inverse just confuses things, at
least for our purposes.

My suggestion: If create_matrix () returns a 3x3, keep the inverse
Jabocian computation out of create_matrix (). 

Because I am far from certain that there would ever be a need to do
matrix operations on the inverse Jacobian, I actually am not even sure
that it is necessary to store it in an explicit matrix type. For
documentation sake? Can anyone foresee a use for the inverse Jacobian
matrix being stored in a 3x3?

Nicolas Robidoux