- extern void color_to_rgba (Color, double& r, double& g, double& b, double& a);
- extern Color rgba_to_color (double r, double g, double b, double a);
+ extern LIBCANVAS_API void set_source_rgba (cairo_t*, Color);
+ extern LIBCANVAS_API void set_source_rgb_a (cairo_t*, Color, float alpha); //override the color's alpha