[cairo] How cairo_pattern_set_matrix() works?

[Silenio Quarti]

Owen Taylor <otaylor at redhat.com> wrote on 03/18/2005 01:15:14 PM:

> Silenio Quarti wrote:
> > What cairo_pattern_set_matrix() should do? Should it affect every
> > individual cell or the whole pattern coordinate system? It seems also
> > that the matrix have the inverse effect. If the matrix scaling portion
> > is 0.5, it actually enlarges the image, instead of reducing it.
> > 
> > For example, in the code below I was expecting 4 surfaces/pixmaps
> > of reduced size (30x30) to be drawn completely (one in which corner of 
the
> > rectangle (50,50, 60,60)), but instead the output is partial enlarged
> > images.
> > 
> > Is this the expected behavior?
> 
> The matrix for a pattern defines a mapping from user space to pattern
> space. So, if we set a scale on the pattern matrix of 0.5, that means
> that for every unit we move in user space, we move 0.5 units in pattern
> space ... that is, enlargement.

Ok, that makes sense. So if I change the matrix as follow:

cairo_matrix_translate(matrix, -50, -50);
cairo_matrix_scale(matrix, 2, 2);

shouldn't I get 4 reduced images one in which corner
of the rectangle (50,50,60,60)? With snapshot 0.4.0,
the output is only one image in the top/left corner of the
rectangle. The problem is that only one quarter of the
rectangle is filled. It seems that the pattern cell 
was not affected.

Thanks!
Silenio