[cairo] const usage in API

[Hakki Dogusan]

Hi,

Some functions use const for parameters, but some not. Is there a rule?

ex:
cairo_public void
cairo_scaled_font_extents (cairo_scaled_font_t  *scaled_font, 
      	cairo_font_extents_t *extents);

cairo_public void
cairo_set_matrix (cairo_t *cr,
	const cairo_matrix_t *matrix);



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Regards,
Hakki Dogusan