Implement Transition Tree plugin

[ZombieHDGaming]

Turns the plugin template into the full Transition Tree plugin: ~4,400 lines across a model, resolution engine, Qt editor, and obs-websocket vendor.

How it applies transitions

Same mechanism Exeldro's Transition Table uses, because it's the only one OBS supports: the plugin never performs a transition itself. Before each switch it writes OBS's own per-scene override (transition / transition_duration private settings) onto every scene that could be the next destination, and OBS's GetOverrideTransition() picks it up. Overrides are recomputed on transition_start, channel_change and SCENE_CHANGED, for every canvas.

One improvement over the reference: the plugin tracks which scenes it wrote to, and only clears those. A transition override you set in OBS yourself survives unless a mark actually targets that scene.

What's implemented

Presets — each is local (scene collection blob) or global (global-presets.json in the plugin config dir), switchable per preset. Every scene collection remembers its own active preset. Global presets whose scenes are missing from the current collection are kept, shown in red, and skipped at runtime.

Multiple transitions per mark — sequential, random, random-no-immediate-repeat, and weighted, with per-candidate duration and weight.

The selection timing is the subtle part: picks are armed on arrival at a scene and held until departure, so each switch consumes exactly one random roll rather than re-rolling on every incidental signal. Sequential positions advance only for the mark that actually fired, detected by comparing the program scene against the armed pick.

Scene matching — explicit scene lists (multi-scene), Any, and Any except … on both sides. Resolution is most-specific-first, from-side dominant (A → not-C beats Any → D, loses to A → D), ties going to the first-listed mark.

Editor — a tree grouped by from-scene with a detail panel. This is the fix for the reported Transition Table UX problem: there, fromCombo/toCombo are simultaneously the add-row inputs and the table filter, so picking a scene to add a mark hides every unrelated row. Here the search box only filters the view and "Add Mark" is a separate button, so narrowing the list can never hide the controls needed to create one.

Hotkeys — per-preset activation (registered dynamically, bindings survive renames by matching on hotkey id), next/previous preset, and a global enable/disable pair.

obs-websocket — vendor transition-tree with preset and mark control plus a preset_changed event, and Transition Table's get_transition / set_transition / get_table under the same names for script compatibility. Requests are marshalled onto the Qt main thread so they stay race-free while still answering synchronously.

Import/export — versioned JSON, accepting our format, a bare preset, and Transition Table exports. If a scene collection has Transition Table data and no Transition Tree data, the plugin offers once to migrate it.

Creating transitions — OBS exposes no API for adding a transition to its list (obs_frontend_get_transitions only reads it; OBS resolves names against the main window's transitions combo, and only what's in that combo persists). The "New Transition…" button therefore drives OBS's own transitionAdd button, so the transition is initialised, named and saved exactly as if added from the transitions dock. Injecting a private source into the combo directly was rejected — it skips OBS's private InitTransition(), which wires the transition_stop signals that re-enable the transition widgets.

Verification

• All five translation units compile clean (-Wall -Wextra) against the real OBS 31.1.1 headers and Qt6, including the generated moc output.
• CMakeLists.txt configures correctly (fails only at find_package(libobs), expected without OBS installed).
• clang-format-19 and gersemi both clean, matching what CI runs.

Not verified: runtime behaviour. There's no OBS instance here, so this proves it compiles, not that transitions fire correctly. Worth a local smoke test of a scene switch, a preset hotkey, and the sequential/weighted picking before merging.

Notes

• Requires OBS 31.1+ (the canvas API).
• Running Transition Table alongside is not supported — both write the same per-scene settings. Detected at load, logged, and surfaced once in the window.
• Metadata set to transition-tree / Voidscape Development / https://voidscape.dev / dev.voidscape.transition-tree, version 0.1.0. GPL-2.0, crediting Transition Table as prior art.

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https://claude.ai/code/session_01MBcrZqvWJy32tBVg5i9VD9

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