/* Helpers for get_preferred_width()/get_preferred_height() ClutterActor vfuncs */
void st_theme_node_adjust_for_height       (StThemeNode  *node,
                                            float        *for_height);
void st_theme_node_adjust_preferred_width  (StThemeNode  *node,
                                            float        *min_width_p,
                                            float        *natural_width_p);
void st_theme_node_adjust_for_width        (StThemeNode  *node,
                                            float        *for_width);
void st_theme_node_adjust_preferred_height (StThemeNode  *node,
                                            float        *min_height_p,
                                            float        *natural_height_p);

Do not result in very readable code:

 st_theme_node_adjust_for_height (theme_node, &for_height);

Does that adjust the theme node for a height? or?

is pretty opaque in what it does. Various suggestions in bug 595993. I think my favorite idea at this point is:

float st_theme_node_get_content_height   (StThemeNode  *node,
                                          float         total_height);
void  st_theme_node_get_preferred_width  (StThemeNode  *node,
                                          float         content_min_width,
                                          float         content_natural_width,
                                          float        *min_width_p,
                                          float        *natural_width_p);
float st_theme_node_get_content_width    (StThemeNode  *node,
                                          float         total_width);
void  st_theme_node_get_preferred_height (StThemeNode  *node,
                                          float         content_min_height,
                                          float         content_natural_height,
                                          float        *min_width_p,
                                          float        *natural_width_p);

Though to really get the readability increase from that, you need to add extra locals content_height, content_min_width, content_natural_width, so it's bit of typing to fix everything up.