Fix event pumping with non-owned platforms.

Tested with WebGL and macOS.

filament/src/Engine.cpp

@@ -109,8 +109,6 @@ FEngine* FEngine::create(Backend backend, Platform* platform, void* sharedGLCont
     // Normally we launch a thread and create the context and Driver from there (see FEngine::loop).
     // In the single-threaded case, we do so in the here and now.
     if (!UTILS_HAS_THREADING) {
-        // we don't own the external context at that point, set it to null
-        instance->mPlatform = nullptr;
         if (platform == nullptr) {
             platform = DefaultPlatform::create(&instance->mBackend);
             instance->mPlatform = platform;
@@ -406,13 +404,8 @@ void FEngine::flushAndWait() {
 // -----------------------------------------------------------------------------------------------
 
 int FEngine::loop() {
-    // we don't own the external context at that point, set it to null
-    Platform* platform = mPlatform;
-    mPlatform = nullptr;
-
-    if (platform == nullptr) {
-        platform = DefaultPlatform::create(&mBackend);
-        mPlatform = platform;
+    if (mPlatform == nullptr) {
+        mPlatform = DefaultPlatform::create(&mBackend);
         mOwnPlatform = true;
         slog.d << "FEngine resolved backend: ";
         switch (mBackend) {
@@ -460,7 +453,7 @@ int FEngine::loop() {
     JobSystem::setThreadName("FEngine::loop");
     JobSystem::setThreadPriority(JobSystem::Priority::DISPLAY);
 
-    mDriver = platform->createDriver(mSharedGLContext);
+    mDriver = mPlatform->createDriver(mSharedGLContext);
     mDriverBarrier.latch();
     if (UTILS_UNLIKELY(!mDriver)) {
         // if we get here, it's because the driver couldn't be initialized and the problem has

filament/src/details/Engine.h

@@ -268,6 +268,10 @@ public:
     // flush the current buffer
     void flush();
 
+    /**
+     * Processes the platform's event queue when called from the platform's event-handling thread.
+     * Returns false when called from any other thread.
+     */
     bool pumpPlatformEvents() {
         return mPlatform->pumpEvents();
     }