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64 lines
2.1 KiB
Text
64 lines
2.1 KiB
Text
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0) definitions:
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All pads without further specifiers are assumed to belong to the element
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in question. The pad's peer is always denoted with ->peer. If there's
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question, pads will be prefixed with self-> and other-> as necessary.
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All elements in this document have at most one source and one sink pad,
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called srcpad and sinkpad. Multi-pad cases are supposed to be simple
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extrapolations except in a couple strange cases, to be covered elsewhere.
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1) loop functions:
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A loop function will call gst_pad_pull(sinkpad), do something, and call
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gst_pad_push(srcpad).
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gst_pad_pull first checks to see if there's a buffer in the pen. If not,
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it calls that pad's pullfunc handler, passing it the peer pad. When that
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finishes, we check again and return the buffer. If no buffer, we squawk.
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The pullfunc handler simply causes a cothread switch to the peer pad's
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context;
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gst_pad_push places the buffer in the peer pad's pen, and calls the local
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pad's pushfunc. The pushfunc simply causes a switch to the peer pad's
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context.
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2) chain functions
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The loopfunc constructed around a chain function starts by finding all
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sink pads. For each sink pad, it calls gst_pad_pull. This causes a
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switch to the peer pad's context and a buffer to appear, which is
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returned. The pad is the handed off to the chain function, which
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presumably does some processing and calls gst_pad_push(), which causes a
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context switch to that pad's peer.
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3) source
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The loopfunc must repeatedly call the srcpad's pull
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--------------------------------- ---------------------------------
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srcpad | | sinkpad
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GstPad *peer; | <-p-> | GstPad *peer;
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pointer to peer pad | | pointer to peer pad
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funcptr *pushfunc; | --s-> | funcptr *pushfunc;
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causes switch to peer ctx | | element uses buffer in pen,
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funcptr *pullfunc; | <-s-- | funcptr *pullfunc;
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element puts buffer in pen, | | causes switch to peer ctx
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calls gst_pad_push() | |
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funcptr *pullregion func | <-s-- | funcptr *pullregionfunc;
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element puts region in pen | | causes switch to peer ctx
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calls gst_pad_push() | |
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--------------------------------- ---------------------------------
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