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Streaming a KDE desktop showed two cursors: the one the user was moving, and a
second one sitting underneath it that never moved. It was not KDE's — KWin 6.7.3
in cursor-as-metadata mode calls `setRenderCursor(false)` on every recorded buffer
and hands the cursor item to an exclusive `ItemTreeView`, so `shouldRenderItem()`
skips it and no pointer is ever painted into that stream. It was ours.
Both clients declared the render model as `captured && desktop`, so ANY released
pointer handed compositing back to the host. But releasing does not remove the
local cursor — it restores the ordinary window arrow over the video. The host then
blends its own pointer in underneath, and since a released client forwards no
motion, nothing drives it: it stays frozen wherever the host pointer was last left.
Caught live on the host with the render-model diag:
cursor diag: client_draws=false blended=true live=Some((-1, 622, true))
x = -1 — parked on the streamed output's left edge, unchanged sample after sample,
while the user moved their own cursor around freely. Engaging capture flipped it to
`client_draws=true blended=false` and the duplicate vanished, which is why it only
looked "stuck when not dragging": dragging means engaged, and engaged was the one
state that behaved.
The host may composite ONLY while the client holds a grabbed, hidden pointer — the
capture model, engaged — which is the single state with no local cursor on screen.
Released now counts as "the client draws it": the host stops compositing and keeps
forwarding shape/state over the channel (the forwarder ticks on this side of the
flip), so re-engaging is seamless and the client's cached shape stays warm.