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302 lines
9.2 KiB
Text
302 lines
9.2 KiB
Text
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Ghostpads
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---------
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GhostPads are used to build complex compound elements out of
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existing elements. They are used to expose internal element pads
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on the complex element.
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Some design requirements
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- Must look like a real GstPad on both sides.
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- target of Ghostpad must be changeable
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* a GhostPad is implemented using a smaller GstProxyPad class:
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GstProxyPad
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(------------------)
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| GstPad |
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|------------------|
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| GstPad *target |
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(------------------)
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GstGhostPad
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(------------------) -\
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| GstPad | |
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|------------------| > GstProxyPad
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| GstPad *target | |
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|------------------| -/
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| GstPad *internal |
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(------------------)
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Some use case follow with a description of how the datastructure
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is modified.
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* Creating a ghostpad with a target:
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gst_ghost_pad_new (char *name, GstPad *target)
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1) create new GstGhostPad X
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2) X name set to @name
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3) X direction is the same as the target
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4) the target is set to @target
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5) internal is NULL
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6) link/unlink and activate functions are set up
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on GstGhostPad.
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(--------------
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(- X --------) |
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| | |------)
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| target *------------------> | sink |
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|------------| |------)
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| internal *---->// (--------------
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(------------)
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- Automatically takes same direction as target.
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- target is filled in automatically.
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* Creating a ghostpad without a target
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gst_ghost_pad_new_notarget (char *name, GstPadDirection dir)
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1) create new GstGhostPad X
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2) X name set to @name
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3) X direction is @dir
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4) internal is NULL
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5) link/unlink and activate functions are set up
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on GstGhostPad.
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(- X --------)
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| target *------>//
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|------------|
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| internal *---->//
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(------------)
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- allows for setting the target later
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* Setting target on an untargetted unlinked ghostpad
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gst_ghost_pad_set_target (char *name, GstPad *newtarget)
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(- X --------)
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| target *------>//
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|------------|
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| internal *---->//
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(------------)
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1) assert direction of newtarget == X direction
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2) target is set to newtarget
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(--------
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(- X --------) |
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| | |------)
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| target *------------->| sink |
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|------------| |------)
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| internal *--->// (--------
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(------------)
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* Setting target on an targetted unlinked ghostpad
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gst_ghost_pad_set_target (char *name, GstPad *newtarget)
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(--------
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(- X --------) |
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| | |------)
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| target *------------->| sink |
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|------------| |------)
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| internal *--->// (--------
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(------------)
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1) assert direction of newtarget == X direction
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2) target is set to newtarget
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(--------
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(- X --------) |
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| | |------)
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| target *------------->| sink |
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|------------| |------)
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| internal *--->// (--------
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(------------)
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* Linking a pad to an untargetted ghostpad:
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gst_pad_link (src, X)
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(- X --------)
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| target *------>//
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|------------|
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| internal *---->//
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(------------)
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-------)
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(-----|
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| src |
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(-----|
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-------)
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1) link function is called
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a) new GstProxyPad Y is created
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b) Y direction is same as peer
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c) Y target is set to peer
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d) X internal pad is set to Y
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e) Y is activated in the same mode as X
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f) core makes link from src to X
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(- X --------)
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| target *----->//
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>|------------|
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(real pad link) / | internal * |
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/ (----------|-)
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/ |
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-------) / V
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| / (- Y ------)
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(-----|/ | |
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| src |<-------------* target |
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(-----| (----------)
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-------)
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* Linking a pad to a targetted ghostpad:
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gst_pad_link (src, X)
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(--------
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(- X --------) |
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| | |------)
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| target *------------->| sink |
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|------------| |------)
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| internal *--->// (--------
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(------------)
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-------)
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(-----|
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| src |
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(-----|
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-------)
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1) link function is called
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a) new GstProxyPad Y is created
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b) Y direction is same as peer
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c) Y target is set to peer
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d) X internal pad is set to Y
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e) link is made from Y to X target (sink)
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f) Y is activated in the same mode as X
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g) core makes link from src to X
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(--------
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(- X --------) |
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| | |------)
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| target *------------->| sink |
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>|------------| >|------)
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(real pad link) / | internal * | / (--------
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/ (----------|-) /
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/ | /
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-------) / V / (real pad link)
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| / (- Y ------) /
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(-----|/ | |/
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| src |<-------------* target |
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(-----| (----------)
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-------)
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* Setting target on untargetted linked ghostpad:
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gst_ghost_pad_set_target (char *name, GstPad *newtarget)
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(- X --------)
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| target *----->//
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>|------------|
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(real pad link) / | internal * |
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/ (----------|-)
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/ |
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-------) / V
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| / (- Y ------)
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(-----|/ | |
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| src |<-------------* target |
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(-----| (----------)
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-------)
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1) assert direction of newtarget == X direction
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2) X target is set to newtarget
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3) Y (X internal) is linked to newtarget
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(--------
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(- X --------) |
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| target *------------->| sink |
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>|------------| >|------)
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(real pad link) / | internal * | / (--------
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/ (----------|-) /
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/ | /
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-------) / V / (real pad link)
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| / (- Y ------) /
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(-----|/ | |/
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| src |<-------------* target |
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(-----| (----------)
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-------)
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* Setting target on targetted linked ghostpad:
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gst_ghost_pad_set_target (char *name, GstPad *newtarget)
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(--------
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(- X --------) |
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| target *------------->| sink |
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>|------------| >|------)
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(real pad link) / | internal * | / (--------
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/ (----------|-) /
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/ | /
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-------) / V / (real pad link)
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| / (- Y ------) /
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(-----|/ | |/
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| src |<-------------* target |
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(-----| (----------)
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-------)
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1) assert direction of newtarget == X direction
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2) Y and X target are unlinked
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2) X target is set to newtarget
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3) Y (X internal) is linked to newtarget
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(--------
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(- X --------) |
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| target *------------->| sink |
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>|------------| >|------)
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(real pad link) / | internal * | / (--------
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/ (----------|-) /
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/ | /
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-------) / V / (real pad link)
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| / (- Y ------) /
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(-----|/ | |/
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| src |<-------------* target |
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(-----| (----------)
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-------)
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