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ERROR_GRAPHICS_SOURCE_ALREADY_IN_SET
ERROR_GRAPHICS_SOURCE_ALREADY_IN_SET occurs when code adds a video present source ID that the set already contains. A source represents a scan-out surface producer. One source may feed more than one target in a clone topology, but that does not make the source ID appear multiple times in a set of sources.
Check the topology-building loop rather than the monitor hardware first. A common design error is to add the source once per present path, even though several paths can originate from the same source. Enumerate unique source IDs separately from path records, and keep path multiplicity in the topology interface where it belongs.
How to distinguish a duplicate source from valid cloning
- Count unique
VidPnSourceIdvalues independently of path count. - Treat two paths with the same source and different targets as one source with two outputs.
- Verify that retry logic does not append to a set left populated by an earlier attempt.
- Log source IDs in decimal and hexadecimal to expose sentinel or uninitialized values.
Microsoft: VidPN sources, targets, and paths
Microsoft: counting paths from a source
Microsoft: VidPN topology interface
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