Rephrase the cookie documentation
@@ -155,40 +155,41 @@ typedef struct clap_param_info {
clap_param_info_flags flags;
- // This value is optional and set by the plugin. The host will
- // set it on all subsequent events regarding this param_id
- // or set the cookie to nullptr if the host chooses to
- // not implement cookies.
+ // This value is optional and set by the plugin.
+ // Its purpose is to provide a fast access to the
+ // plugin parameter objects by caching its pointer.
+ // For instance:
//
- // The plugin must gracefully handle the case of a cookie
- // which is nullptr, but can safely assume any cookie
- // which is not nullptr is the value it issued.
- //
- // It is very strongly recommended that the host implement
- // cookies. Some plugins may have noticably reduced
- // performance when addressing params in hosts without cookies.
- //
- // The cookie's purpose is to provide a fast access to the
- // plugin parameter objects. For instance:
- //
- // in clap_plugin_params.get_info
+ // in clap_plugin_params.get_info():
// Parameter *p = findParameter(param_id);
// param_info->cookie = p;
//
- // later, in clap_plugin.process:
+ // later, in clap_plugin.process():
//
- // Parameter *p{nullptr};
- // if (evt->cookie) [[likely]]
- // p = (Parameter *)evt->cookie;
- // else
- // p = -- alternate mechanism --
+ // Parameter *p = (Parameter *)event->cookie;
+ // if (!p) [[unlikely]]
+ // p = findParameter(event->param_id);
//
- // where "alternate mechanism" is a mechanism the plugin implements
+ // where findParameter() is a function the plugin implements
// to map parameter ids to internal objects.
//
- // The host should make no assumption about the
- // value of the cookie other than passing it back to the plugin or
- // replacing it with nullptr.
+ // The host will either provide the cookie as issued or nullptr
+ // in events addressing parameters.
+ //
+ // The plugin must gracefully handle the case of a cookie
+ // which is nullptr, but can safely assume any cookie
+ // which is not nullptr is the value it issued.
+ //
+ // The host should provide the cookie if its retrival is cheaper
+ // than an hastable lookup, otherwise the plugin may as well do
+ // the parameter lookup.
+ //
+ // TIP: the host may build a cached array of parameters info
+ // and internally work with parameter index, that way the retrival cost
+ // of the cookie is equivalent to an array access.
+ //
+ // The host should make no assumption about the value of the cookie
+ // other than passing it back to the plugin or replacing it with nullptr.
//
// Once set, the cookie is valid until invalidated by a call to
// clap_host_params->rescan(CLAP_PARAM_RESCAN_ALL) or when the plugin is
