What I tried to do with the gegl_interpolator was in fact what gimp is
doing in gimpdrawable-transform,
Gimp only downsamples in the scale-funcs not during the transformation .
I'm not sure if it is possible to corectly downsample during transformation.
So the resampler should use a transformation matrix, and take source
coördinates.
instead of :
matrix3_copy (inverse, matrix);
matrix3_invert (inverse);
fu = du = inverse[0][0] * dest->x + inverse[0][1] * dest->y + inverse[0][2] - src->x;
fv = dv = inverse[1][0] * dest->x + inverse[1][1] * dest->y + inverse[1][2] - src->y;
for (dest_ptr = dest_buf, y = 0; y < dest->height; y++)
{
for (x = 0; x < dest->width; x++)
{
gegl_interpolator_get (interpolator, fu, fv, dest_buf);
fu += inverse [0][0];
fv += inverse [1][0];
}
du += inverse [0][1];
dv += inverse [1][1];
fu = du;
fv = dv;
...
}
The transformed coordinates should be calculated within the resampler.
gegl_resampler_set_matrix(resampler, matrix);
for (y = 0; y < dest->height; y++)
{
for (x = 0; x < dest->width; x++)
{
gegl_resampler_get (resampler, x, y, dest_buf);
}
...
}
The gegl_resampler_get should then calculate the number of transformed
coordinates needed by the
resampling method (lanczos/bicubic/bilinear/nearest) as in
gimpdrawable-transform.
ca= cos a
sa = sin a
. = don't touch
gegl_resampler_set_matrix_identity()
| 1 0 0 |
| 0 1 0 |
| 0 0 1 |
gegl_resampler_set_scale(x, y)
| *sy . 0 |
| . *sy 0 |
| . . 1 |
gegl_resampler_set_translscale(tx, ty)
| . . 0 |
| . . 0 |
| tx ty 1 |
gegl_resampler_set_rotate(a)
| *ca *sa 0 |
| *-sa *ca 0 |
| . . 1 |
gegl_resampler_set_matrix(a,b,c,d,e,f )
| a d 0 |
| b e 0 |
| c f 1 |
Geert
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