|Cairo: A Vector Graphics Library|
Like patterns, surfaces, which use only the cairo_surface_t type in the C API should be broken up into a hierarchy of types in a language binding.
cairo_surface_t cairo_image_surface_t cairo_atsui_surface_t cairo_win32_surface_t cairo_xlib_surface_t
Unlike patterns, the constructors and methods on these types are clearly named, and can be trivially associated with the appropriate subtype. Many language bindings will want to avoid binding the platform-specific subtypes at all, since the methods on these types are not useful without passing in native C types. Unless there is a language binding for Xlib available, there is no way to represent a XLib Display * in that language.
This doesn't mean that platform-specific surface types can't be used in a language binding that doesn't bind the constructor. A very common situation is to use a cairo language binding in combination with a binding for a higher level system like the GTK+ widget toolkit. In such a situation, the higher level toolkit provides ways to get references to platform specific surfaces.
methods are provided for use in language bindings, and should
not be directly exposed to applications. One example of the use
of these functions in a language binding is creating a binding for:
cairo_image_surface_create_for_data(unsigned char *data, cairo_format_t format, int width, int height, int stride);
The memory block passed in for
data must be
kept around until the surface is destroyed, so the language
binding must have some way of determining when that happens. The
way to do this is to use the
Some languages may not have a suitable “pointer to a block of
data” type to pass in for
data. And even
where a language does have such a type, the user will be
frequently able to cause the backing store to be reallocated
to a different location or truncated. Should we recommend a
standard type name and binding for a buffer object here?