feat(vars): Add obsPreviousSceneName variable (#3057)

src/backend/integrations/builtin/obs/obs-integration.ts

@@ -44,6 +44,7 @@ import GroupNameEventFilter from "./filters/group-name-filter";
 import SceneNameEventFilter from "./filters/scene-name-filter";
 
 import { SceneNameVariable } from "./variables/scene-name-variable";
+import { PreviousSceneNameVariable } from "./variables/previous-scene-name";
 import { SceneCollectionNameVariable } from "./variables/scene-collection-name";
 import { IsConnectedVariable } from "./variables/is-connected";
 import { IsStreamingVariable } from "./variables/is-streaming";
@@ -169,6 +170,7 @@ class ObsIntegration
         FilterManager.registerFilter(SceneNameEventFilter);
 
         ReplaceVariableManager.registerReplaceVariable(SceneNameVariable);
+        ReplaceVariableManager.registerReplaceVariable(PreviousSceneNameVariable);
         ReplaceVariableManager.registerReplaceVariable(SceneCollectionNameVariable);
         ReplaceVariableManager.registerReplaceVariable(IsConnectedVariable);
         ReplaceVariableManager.registerReplaceVariable(IsStreamingVariable);

src/backend/integrations/builtin/obs/obs-remote.ts

@@ -61,6 +61,8 @@ let groupInfos: Array<CachedGroupInfo> = [];
 let previewSceneName: string | null;
 // The cached program scene name.
 let programSceneName: string;
+// The cached previous program scene name.
+let previousProgramSceneName: string;
 
 const TEXT_SOURCE_IDS = ["text_gdiplus_v2", "text_gdiplus_v3", "text_ft2_source_v2"];
 
@@ -179,6 +181,8 @@ async function setupRemoteListeners() {
     });
 
     obs.on("SceneTransitionStarted", async ({ transitionName }) => {
+        previousProgramSceneName = programSceneName || "";
+
         programSceneName = (await obs.call("GetCurrentProgramScene"))?.sceneName || "";
         eventManager?.triggerEvent(
             OBS_EVENT_SOURCE_ID,
@@ -663,6 +667,10 @@ export function getCurrentSceneName(): string {
     return programSceneName;
 }
 
+export function getPreviousSceneName(): string {
+    return previousProgramSceneName;
+}
+
 export async function setCurrentScene(sceneName: string): Promise<void> {
     if (!connected) {
         return;

src/backend/integrations/builtin/obs/variables/previous-scene-name.ts

@@ -0,0 +1,15 @@
+import { ReplaceVariable } from "../../../../../types/variables";
+import { getPreviousSceneName } from "../obs-remote";
+
+export const PreviousSceneNameVariable: ReplaceVariable = {
+    definition: {
+        handle: "obsPreviousSceneName",
+        description:
+      "The name of the previous OBS scene. If OBS isn't running, it returns 'Unknown'.",
+        possibleDataOutput: ["text"],
+        categories: ["advanced", "integrations", "obs"]
+    },
+    evaluator: () => {
+        return getPreviousSceneName() ?? "Unknown";
+    }
+};