URI Map Feature. More...
|Opaque pointer to host data. |
|uint32_t(*||uri_to_id )(LV2_URI_Map_Callback_Data callback_data, const char *map, const char *uri)|
|Get the numeric ID of a URI from the host. |
URI Map Feature.
To support this feature the host must pass an LV2_Feature struct to the plugin's instantiate method with URI "http://lv2plug.in/ns/ext/uri-map" and data pointed to an instance of this struct.
Opaque pointer to host data.
The plugin MUST pass this to any call to functions in this struct. Otherwise, it must not be interpreted in any way.
|uint32_t(* LV2_URI_Map_Feature::uri_to_id)(LV2_URI_Map_Callback_Data callback_data, const char *map, const char *uri)|
Get the numeric ID of a URI from the host.
|callback_data||Must be the callback_data member of this struct.|
|map||The 'context' of this URI. Certain extensions may define a URI that must be passed here with certain restrictions on the return value (e.g. limited range). This value may be NULL if the plugin needs an ID for a URI in general. Extensions SHOULD NOT define a context unless there is a specific need to do so, e.g. to restrict the range of the returned value.|
|uri||The URI to be mapped to an integer ID.|
This function is referentially transparent; any number of calls with the same arguments is guaranteed to return the same value over the life of a plugin instance (though the same URI may return different values with a different map parameter). However, this function is not necessarily very fast: plugins SHOULD cache any IDs they might need in performance critical situations.
The return value 0 is reserved and indicates that an ID for that URI could not be created for whatever reason. Extensions MAY define more precisely what this means in a certain context, but in general plugins SHOULD handle this situation as gracefully as possible. However, hosts SHOULD NOT return 0 from this function in non-exceptional circumstances (e.g. the URI map SHOULD be dynamic). Hosts that statically support only a fixed set of URIs should not expect plugins to function correctly.