Context

#GstContext is a container object used to store contexts like a device context, a display server connection and similar concepts that should be shared between multiple elements.

Applications can set a context on a complete pipeline by using gst_element_set_context(), which will then be propagated to all child elements. Elements can handle these in #GstElementClass.set_context() and merge them with the context information they already have.

When an element needs a context it will do the following actions in this order until one step succeeds: 1. Check if the element already has a context 2. Query downstream with GST_QUERY_CONTEXT for the context 3. Query upstream with GST_QUERY_CONTEXT for the context 4. Post a GST_MESSAGE_NEED_CONTEXT message on the bus with the required context types and afterwards check if a usable context was set now 5. Create a context by itself and post a GST_MESSAGE_HAVE_CONTEXT message on the bus.

Bins will catch GST_MESSAGE_NEED_CONTEXT messages and will set any previously known context on the element that asks for it if possible. Otherwise the application should provide one if it can.

#GstContexts can be persistent. A persistent #GstContext is kept in elements when they reach %GST_STATE_NULL, non-persistent ones will be removed. Also, a non-persistent context won't override a previous persistent context set to an element.

class Context {

protected

GstContext* gstContext;

protected

bool ownedRef;

GstContext* getContextStruct(bool transferOwnership);

void* getStruct();

this(GstContext* gstContext, bool ownedRef);

static GType getType();

this(string contextType, bool persistent);

string getContextType();

Structure getStructure();

bool hasContextType(string contextType);

bool isPersistent();

Structure writableStructure();

}

Constructors

this this(GstContext* gstContext, bool ownedRef): Sets our main struct and passes it to the parent class.
this this(string contextType, bool persistent): Create a new context.

Members

Functions

getContextStruct GstContext* getContextStruct(bool transferOwnership): Get the main Gtk struct
getContextType string getContextType(): Get the type of @context.
getStruct void* getStruct(): the main Gtk struct as a void*
getStructure Structure getStructure(): Access the structure of the context.
hasContextType bool hasContextType(string contextType): Checks if @context has @context_type.
isPersistent bool isPersistent(): Check if @context is persistent.
writableStructure Structure writableStructure(): Get a writable version of the structure.

Static functions

getType GType getType()

Variables

gstContext GstContext* gstContext;: the main Gtk struct
ownedRef bool ownedRef;: Undocumented in source.