Plug-in distributors (PIDs) are a way to extend the functionality of the
filter graph manager. A plug-in distributor is a COM object that the filter
graph manager aggregates at run time. Applications obtain access to the PID
through the filter graph manager.
PIDs
是一种扩展
filter graph manager
功能的方法。一个
PIDs
是一个
filter graph manager
在运行时聚合的
COM
对象。应用程序通过
filter graph manager
获得访问
PID
的权限。
When the filter graph manager is queried for an interface that it does not
support, it searches the registry for a key with the following form:
当
filter graph manager
被询问一个它不支持的接口的时候，它就到注册表的
HKEY_CLASSES_ROOT/Interface/IID/Distributor
KEY
中搜索。
IID
is a string containing the interface
identifier. If the registry entry exists, the value of the entry defines the
class identifier (CLSID) of a PID that supports the interface. The filter graph
manager aggregates the PID and returns an interface pointer, thereby acting as
the outer IUnknown
for the PID. When the application calls methods on
the interface, it is actually calling them on the PID. However, the existence
of the PID is transparent to the application
。
IID
是一个包含接口标识的字符串。如果注册表条目存在，那个条目的值就是支持这个接口的
PID
的类标识（
CLSID
）。
filter graph manager
聚合
PID
并返回接口指针，当应用程序在接口上调用方法，实际上是在
PID
上调用方法。对于应用程序来说，
PID
是透明的。
The term distributor
stems from the fact that a PID can query its
outer IUnknown
pointer for interfaces on the filter graph manager. By
calling the IFilterGraph::EnumFilters
method, the PID can
enumerate the filters in the graph and distribute method calls to those
filters. In this way, a PID can serve as a single control point for the
application to call methods on filters.
术语
distributor
源自
PID
能在
filter graph manager
上为接口询问它外部的
IUnknown
指针。通过调用
IFilterGraph::EnumFilter
方法，
PID
可以枚举
graph
中的
filter
并分配
filter
调用的方法。用这种方法，
PID
可以为应用程序在
filter
上调用方法充当一个控制点。
When the filter graph manager aggregates a PID, it queries the PID for the
IDistributorNotify
interface. If the PID
supports this interface, the filter graph manager uses it to notify the PID
about changes in the graph:
当
filter graph manager
聚合一个
PID
，它就询问
PID
的
IDistributorNotify
接口。如果
PID
支持这个接口，
filter graph manager
就使用这个接口通知
PID
一下
graph
的变化：
·
When the filter graph switches between
run, paused, and stopped states, it calls IDistributorNotify::Run
, IDistributorNotify::Pause
, or IDistributorNotify::Stop
.
·
当
filter graph
在运行，暂停和停止之间切换状态时，它调用
IDistributorNotify::Run
，
IDistributorNotify::Pasuse
，或者
IDistributorNotify::Stop
。
·
When a reference clock is set, the filter
graph manager calls IDistributorNotify::SetSyncSource
.
·
当参考时钟被设置，
filter graph manager
调用
IDistributorNotify::SetSyncSource
。
·
When filters are added or removed, or pin
connections are changed, the filter graph manager calls IDistributorNotify::NotifyGraphChange
.
·
当
filter
被添加或移除，或者
pin
连接被改变，
filter graph manager
调用
IDistributorNotify::NotifyGraphChange
。
To implement a custom PID, create a COM object that supports aggregation.
It must support an interface that the filter graph manager does not already
support. Optionally, it can support the IDistributorNotify
interface.
要执行通用的
PID
，就要创建一个支持聚合的
COM
对象。必须支持一个
filter graph manager
不支持的接口。它能支持
IDistributorNotify
接口。
If the PID obtains any interface pointers from the filter graph manager,
it should release them immediately. Otherwise, it might create a circular
reference count, which could prevent the filter graph manager from being
destroyed. Holding a reference count on the filter graph manager is unnecessary
in any case, because the filter graph manager controls the PID's lifetime.
如果
PID
从
filter graph manager
获得一些接口指针，它应该立即释放掉。否则，它可能创建循环引用计数。在
filter Graph Manager
上握着引用计数没有必要，因为
filter graph manager
控制
PID
的生命周期。
Because a PID is designed specifically for aggregation by the filter graph
manager, you might want to enforce this in the PID's constructor method. Check
whether the outer IUnknown
pointer is NULL, and if so, return the error
code VFW_E_NEED_OWNER. (See Error and Success Codes
.) Also, to prevent other
objects from aggregating the PID, you can query the outer IUnknown
pointer for the IGraphBuilder
interface. Return an error code
if the object does not expose IGraphBuilder
.
因为
PID
被
filter graph manager
设计特殊的聚合，你可能想在
PID
的构造函数中强制这一点。检测
IUnknown
指针释放为
NULL
，如果为，返回错误码
VFW_E_NEED_OWNER
。为了防止其他对象聚合
PD
，你可以询问
IGrpahBuilder
接口的
IUnknown
指针。如果对象没有暴露
IGraphBuilder
则返回错误码。