diff --git a/libs/vr/libvrflinger/Android.bp b/libs/vr/libvrflinger/Android.bp
index 3e4a42c..4dc669b 100644
--- a/libs/vr/libvrflinger/Android.bp
+++ b/libs/vr/libvrflinger/Android.bp
@@ -72,6 +72,7 @@
     srcs: sourceFiles,
     export_include_dirs: includeFiles,
 
+    clang: true,
     cflags: [
         "-DLOG_TAG=\"vr_flinger\"",
         "-DTRACE=0",
@@ -83,6 +84,9 @@
         "-Wno-error=sign-compare", // to fix later
         "-Wno-unused-variable",
     ],
+    cppflags: [
+        "-std=c++1z"
+    ],
     shared_libs: sharedLibraries,
     whole_static_libs: staticLibraries,
     header_libs: headerLibraries,
diff --git a/libs/vr/libvrflinger/display_service.cpp b/libs/vr/libvrflinger/display_service.cpp
index a18ff1a..87162c0 100644
--- a/libs/vr/libvrflinger/display_service.cpp
+++ b/libs/vr/libvrflinger/display_service.cpp
@@ -177,12 +177,12 @@
 
 Status<display::Metrics> DisplayService::OnGetMetrics(
     pdx::Message& /*message*/) {
-  return {{static_cast<uint32_t>(GetDisplayMetrics().width),
-           static_cast<uint32_t>(GetDisplayMetrics().height),
-           static_cast<uint32_t>(GetDisplayMetrics().dpi.x),
-           static_cast<uint32_t>(GetDisplayMetrics().dpi.y),
-           static_cast<uint32_t>(
-               hardware_composer_.native_display_metrics().vsync_period_ns),
+  const auto& params = hardware_composer_.GetPrimaryDisplayParams();
+  return {{static_cast<uint32_t>(params.width),
+           static_cast<uint32_t>(params.height),
+           static_cast<uint32_t>(params.dpi.x),
+           static_cast<uint32_t>(params.dpi.y),
+           static_cast<uint32_t>(params.vsync_period_ns),
            0,
            0,
            0,
diff --git a/libs/vr/libvrflinger/display_service.h b/libs/vr/libvrflinger/display_service.h
index 316f15a..3090bd1 100644
--- a/libs/vr/libvrflinger/display_service.h
+++ b/libs/vr/libvrflinger/display_service.h
@@ -65,10 +65,6 @@
     hardware_composer_.SetVSyncCallback(callback);
   }
 
-  HWCDisplayMetrics GetDisplayMetrics() {
-    return hardware_composer_.display_metrics();
-  }
-
   void GrantDisplayOwnership() { hardware_composer_.Enable(); }
   void SeizeDisplayOwnership() { hardware_composer_.Disable(); }
   void OnBootFinished() { hardware_composer_.OnBootFinished(); }
diff --git a/libs/vr/libvrflinger/hardware_composer.cpp b/libs/vr/libvrflinger/hardware_composer.cpp
index 5b49645..44ce78c 100644
--- a/libs/vr/libvrflinger/hardware_composer.cpp
+++ b/libs/vr/libvrflinger/hardware_composer.cpp
@@ -50,9 +50,17 @@
 
 const char kRightEyeOffsetProperty[] = "dvr.right_eye_offset_ns";
 
+const char kUseExternalDisplayProperty[] = "persist.vr.use_external_display";
+
 // How long to wait after boot finishes before we turn the display off.
 constexpr int kBootFinishedDisplayOffTimeoutSec = 10;
 
+constexpr int kDefaultDisplayWidth = 1920;
+constexpr int kDefaultDisplayHeight = 1080;
+constexpr int64_t kDefaultVsyncPeriodNs = 16666667;
+// Hardware composer reports dpi as dots per thousand inches (dpi * 1000).
+constexpr int kDefaultDpi = 400000;
+
 // Get time offset from a vsync to when the pose for that vsync should be
 // predicted out to. For example, if scanout gets halfway through the frame
 // at the halfway point between vsyncs, then this could be half the period.
@@ -109,6 +117,11 @@
 #define TRACE_FORMAT(format, ...) \
   TraceArgs PASTE(__tracer, __LINE__) { format, ##__VA_ARGS__ }
 
+// Returns "primary" or "external". Useful for writing more readable logs.
+const char* GetDisplayName(bool is_primary) {
+  return is_primary ? "primary" : "external";
+}
+
 }  // anonymous namespace
 
 HardwareComposer::HardwareComposer()
@@ -132,42 +145,7 @@
 
   request_display_callback_ = request_display_callback;
 
-  HWC::Error error = HWC::Error::None;
-
-  Hwc2::Config config;
-  error = composer->getActiveConfig(primary_display_id, &config);
-
-  if (error != HWC::Error::None) {
-    ALOGE("HardwareComposer: Failed to get current display config : %d",
-          config);
-    return false;
-  }
-
-  error = GetDisplayMetrics(composer, primary_display_id, config,
-                            &native_display_metrics_);
-
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer: Failed to get display attributes for current "
-        "configuration : %d",
-        error.value);
-    return false;
-  }
-
-  ALOGI(
-      "HardwareComposer: primary display attributes: width=%d height=%d "
-      "vsync_period_ns=%d DPI=%dx%d",
-      native_display_metrics_.width, native_display_metrics_.height,
-      native_display_metrics_.vsync_period_ns, native_display_metrics_.dpi.x,
-      native_display_metrics_.dpi.y);
-
-  // Set the display metrics but never use rotation to avoid the long latency of
-  // rotation processing in hwc.
-  display_transform_ = HWC_TRANSFORM_NONE;
-  display_metrics_ = native_display_metrics_;
-
-  // Setup the display metrics used by all Layer instances.
-  Layer::SetDisplayMetrics(native_display_metrics_);
+  primary_display_ = GetDisplayParams(composer, primary_display_id, true);
 
   post_thread_event_fd_.Reset(eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK));
   LOG_ALWAYS_FATAL_IF(
@@ -236,43 +214,38 @@
   }
 }
 
-void HardwareComposer::OnPostThreadResumed() {
-  // Phones create a new composer client on resume and destroy it on pause.
-  // Standalones only create the composer client once and then use SetPowerMode
-  // to control the screen on pause/resume.
-  if (!is_standalone_device_ || !composer_) {
-    composer_.reset(new Hwc2::impl::Composer("default"));
-    composer_callback_ = new ComposerCallback;
-    composer_->registerCallback(composer_callback_);
-    LOG_ALWAYS_FATAL_IF(!composer_callback_->HasDisplayId(),
-        "Registered composer callback but didn't get primary display");
-    Layer::SetComposer(composer_.get());
-    Layer::SetDisplayId(composer_callback_->GetDisplayId());
-  } else {
-    SetPowerMode(true);
-  }
+void HardwareComposer::CreateComposer() {
+  if (composer_)
+    return;
+  composer_.reset(new Hwc2::impl::Composer("default"));
+  composer_callback_ = new ComposerCallback;
+  composer_->registerCallback(composer_callback_);
+  LOG_ALWAYS_FATAL_IF(!composer_callback_->GotFirstHotplug(),
+      "Registered composer callback but didn't get hotplug for primary"
+      " display");
+}
 
-  EnableVsync(true);
+void HardwareComposer::OnPostThreadResumed() {
+  ALOGI("OnPostThreadResumed");
+  EnableDisplay(*target_display_, true);
 
   // Trigger target-specific performance mode change.
   property_set(kDvrPerformanceProperty, "performance");
 }
 
 void HardwareComposer::OnPostThreadPaused() {
+  ALOGI("OnPostThreadPaused");
   retire_fence_fds_.clear();
   layers_.clear();
 
-  if (composer_) {
-    EnableVsync(false);
-  }
-
+  // Phones create a new composer client on resume and destroy it on pause.
+  // Standalones only create the composer client once and then use SetPowerMode
+  // to control the screen on pause/resume.
   if (!is_standalone_device_) {
     composer_callback_ = nullptr;
     composer_.reset(nullptr);
-    Layer::SetComposer(nullptr);
-    Layer::SetDisplayId(0);
   } else {
-    SetPowerMode(false);
+    EnableDisplay(*target_display_, false);
   }
 
   // Trigger target-specific performance mode change.
@@ -305,28 +278,55 @@
       composer_->validateDisplay(display, &num_types, &num_requests);
 
   if (error == HWC2_ERROR_HAS_CHANGES) {
-    // TODO(skiazyk): We might need to inspect the requested changes first, but
-    // so far it seems like we shouldn't ever hit a bad state.
-    // error = hwc2_funcs_.accept_display_changes_fn_(hardware_composer_device_,
-    //                                               display);
+    ALOGE("Hardware composer has requested composition changes, "
+          "which we don't support.");
+    // Accept the changes anyway and see if we can get something on the screen.
     error = composer_->acceptDisplayChanges(display);
   }
 
   return error;
 }
 
-HWC::Error HardwareComposer::EnableVsync(bool enabled) {
-  return composer_->setVsyncEnabled(
-      composer_callback_->GetDisplayId(),
+bool HardwareComposer::EnableVsync(const DisplayParams& display, bool enabled) {
+  HWC::Error error = composer_->setVsyncEnabled(display.id,
       (Hwc2::IComposerClient::Vsync)(enabled ? HWC2_VSYNC_ENABLE
                                              : HWC2_VSYNC_DISABLE));
+  if (error != HWC::Error::None) {
+    ALOGE("Error attempting to %s vsync on %s display: %s",
+        enabled ? "enable" : "disable", GetDisplayName(display.is_primary),
+        error.to_string().c_str());
+  }
+  return error == HWC::Error::None;
 }
 
-HWC::Error HardwareComposer::SetPowerMode(bool active) {
+bool HardwareComposer::SetPowerMode(const DisplayParams& display, bool active) {
+  ALOGI("Turning %s display %s", GetDisplayName(display.is_primary),
+      active ? "on" : "off");
   HWC::PowerMode power_mode = active ? HWC::PowerMode::On : HWC::PowerMode::Off;
-  return composer_->setPowerMode(
-      composer_callback_->GetDisplayId(),
+  HWC::Error error = composer_->setPowerMode(display.id,
       power_mode.cast<Hwc2::IComposerClient::PowerMode>());
+  if (error != HWC::Error::None) {
+    ALOGE("Error attempting to turn %s display %s: %s",
+          GetDisplayName(display.is_primary), active ? "on" : "off",
+        error.to_string().c_str());
+  }
+  return error == HWC::Error::None;
+}
+
+bool HardwareComposer::EnableDisplay(const DisplayParams& display,
+                                     bool enabled) {
+  bool power_result;
+  bool vsync_result;
+  // When turning a display on, we set the power state then set vsync. When
+  // turning a display off we do it in the opposite order.
+  if (enabled) {
+    power_result = SetPowerMode(display, enabled);
+    vsync_result = EnableVsync(display, enabled);
+  } else {
+    vsync_result = EnableVsync(display, enabled);
+    power_result = SetPowerMode(display, enabled);
+  }
+  return power_result && vsync_result;
 }
 
 HWC::Error HardwareComposer::Present(hwc2_display_t display) {
@@ -345,78 +345,105 @@
   return error;
 }
 
-HWC::Error HardwareComposer::GetDisplayAttribute(Hwc2::Composer* composer,
-                                                 hwc2_display_t display,
-                                                 hwc2_config_t config,
-                                                 hwc2_attribute_t attribute,
-                                                 int32_t* out_value) const {
-  return composer->getDisplayAttribute(
-      display, config, (Hwc2::IComposerClient::Attribute)attribute, out_value);
-}
+DisplayParams HardwareComposer::GetDisplayParams(
+    Hwc2::Composer* composer, hwc2_display_t display, bool is_primary) {
+  DisplayParams params;
+  params.id = display;
+  params.is_primary = is_primary;
 
-HWC::Error HardwareComposer::GetDisplayMetrics(
-    Hwc2::Composer* composer, hwc2_display_t display, hwc2_config_t config,
-    HWCDisplayMetrics* out_metrics) const {
-  HWC::Error error;
+  Hwc2::Config config;
+  HWC::Error error = composer->getActiveConfig(display, &config);
 
-  error = GetDisplayAttribute(composer, display, config, HWC2_ATTRIBUTE_WIDTH,
-                              &out_metrics->width);
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer::GetDisplayMetrics: Failed to get display width: %s",
-        error.to_string().c_str());
-    return error;
+  if (error == HWC::Error::None) {
+    auto get_attr = [&](hwc2_attribute_t attr, const char* attr_name)
+        -> std::optional<int32_t> {
+      int32_t val;
+      HWC::Error error = composer->getDisplayAttribute(
+          display, config, (Hwc2::IComposerClient::Attribute)attr, &val);
+      if (error != HWC::Error::None) {
+        ALOGE("Failed to get %s display attr %s: %s",
+            GetDisplayName(is_primary), attr_name,
+            error.to_string().c_str());
+        return std::nullopt;
+      }
+      return val;
+    };
+
+    auto width = get_attr(HWC2_ATTRIBUTE_WIDTH, "width");
+    auto height = get_attr(HWC2_ATTRIBUTE_HEIGHT, "height");
+
+    if (width && height) {
+      params.width = *width;
+      params.height = *height;
+    } else {
+      ALOGI("Failed to get width and/or height for %s display. Using default"
+          " size %dx%d.", GetDisplayName(is_primary), kDefaultDisplayWidth,
+          kDefaultDisplayHeight);
+      params.width = kDefaultDisplayWidth;
+      params.height = kDefaultDisplayHeight;
+    }
+
+    auto vsync_period = get_attr(HWC2_ATTRIBUTE_VSYNC_PERIOD, "vsync period");
+    if (vsync_period) {
+      params.vsync_period_ns = *vsync_period;
+    } else {
+      ALOGI("Failed to get vsync period for %s display. Using default vsync"
+          " period %.2fms", GetDisplayName(is_primary),
+          static_cast<float>(kDefaultVsyncPeriodNs) / 1000000);
+      params.vsync_period_ns = kDefaultVsyncPeriodNs;
+    }
+
+    auto dpi_x = get_attr(HWC2_ATTRIBUTE_DPI_X, "DPI X");
+    auto dpi_y = get_attr(HWC2_ATTRIBUTE_DPI_Y, "DPI Y");
+    if (dpi_x && dpi_y) {
+      params.dpi.x = *dpi_x;
+      params.dpi.y = *dpi_y;
+    } else {
+      ALOGI("Failed to get dpi_x and/or dpi_y for %s display. Using default"
+          " dpi %d.", GetDisplayName(is_primary), kDefaultDpi);
+      params.dpi.x = kDefaultDpi;
+      params.dpi.y = kDefaultDpi;
+    }
+  } else {
+    ALOGE("HardwareComposer: Failed to get current %s display config: %d."
+        " Using default display values.",
+        GetDisplayName(is_primary), error.value);
+    params.width = kDefaultDisplayWidth;
+    params.height = kDefaultDisplayHeight;
+    params.dpi.x = kDefaultDpi;
+    params.dpi.y = kDefaultDpi;
+    params.vsync_period_ns = kDefaultVsyncPeriodNs;
   }
 
-  error = GetDisplayAttribute(composer, display, config, HWC2_ATTRIBUTE_HEIGHT,
-                              &out_metrics->height);
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer::GetDisplayMetrics: Failed to get display height: %s",
-        error.to_string().c_str());
-    return error;
-  }
+  ALOGI(
+      "HardwareComposer: %s display attributes: width=%d height=%d "
+      "vsync_period_ns=%d DPI=%dx%d",
+      GetDisplayName(is_primary),
+      params.width,
+      params.height,
+      params.vsync_period_ns,
+      params.dpi.x,
+      params.dpi.y);
 
-  error = GetDisplayAttribute(composer, display, config,
-                              HWC2_ATTRIBUTE_VSYNC_PERIOD,
-                              &out_metrics->vsync_period_ns);
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer::GetDisplayMetrics: Failed to get display height: %s",
-        error.to_string().c_str());
-    return error;
-  }
-
-  error = GetDisplayAttribute(composer, display, config, HWC2_ATTRIBUTE_DPI_X,
-                              &out_metrics->dpi.x);
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer::GetDisplayMetrics: Failed to get display DPI X: %s",
-        error.to_string().c_str());
-    return error;
-  }
-
-  error = GetDisplayAttribute(composer, display, config, HWC2_ATTRIBUTE_DPI_Y,
-                              &out_metrics->dpi.y);
-  if (error != HWC::Error::None) {
-    ALOGE(
-        "HardwareComposer::GetDisplayMetrics: Failed to get display DPI Y: %s",
-        error.to_string().c_str());
-    return error;
-  }
-
-  return HWC::Error::None;
+  return params;
 }
 
 std::string HardwareComposer::Dump() {
   std::unique_lock<std::mutex> lock(post_thread_mutex_);
   std::ostringstream stream;
 
-  stream << "Display metrics:     " << display_metrics_.width << "x"
-         << display_metrics_.height << " " << (display_metrics_.dpi.x / 1000.0)
-         << "x" << (display_metrics_.dpi.y / 1000.0) << " dpi @ "
-         << (1000000000.0 / display_metrics_.vsync_period_ns) << " Hz"
-         << std::endl;
+  auto print_display_metrics = [&](const DisplayParams& params) {
+    stream << GetDisplayName(params.is_primary)
+           << " display metrics:     " << params.width << "x"
+           << params.height << " " << (params.dpi.x / 1000.0)
+           << "x" << (params.dpi.y / 1000.0) << " dpi @ "
+           << (1000000000.0 / params.vsync_period_ns) << " Hz"
+           << std::endl;
+  };
+
+  print_display_metrics(primary_display_);
+  if (external_display_)
+    print_display_metrics(*external_display_);
 
   stream << "Post thread resumed: " << post_thread_resumed_ << std::endl;
   stream << "Active layers:       " << layers_.size() << std::endl;
@@ -439,7 +466,7 @@
   return stream.str();
 }
 
-void HardwareComposer::PostLayers() {
+void HardwareComposer::PostLayers(hwc2_display_t display) {
   ATRACE_NAME("HardwareComposer::PostLayers");
 
   // Setup the hardware composer layers with current buffers.
@@ -487,14 +514,14 @@
   }
 #endif
 
-  HWC::Error error = Validate(composer_callback_->GetDisplayId());
+  HWC::Error error = Validate(display);
   if (error != HWC::Error::None) {
-    ALOGE("HardwareComposer::PostLayers: Validate failed: %s",
-          error.to_string().c_str());
+    ALOGE("HardwareComposer::PostLayers: Validate failed: %s display=%" PRIu64,
+          error.to_string().c_str(), display);
     return;
   }
 
-  error = Present(composer_callback_->GetDisplayId());
+  error = Present(display);
   if (error != HWC::Error::None) {
     ALOGE("HardwareComposer::PostLayers: Present failed: %s",
           error.to_string().c_str());
@@ -503,7 +530,7 @@
 
   std::vector<Hwc2::Layer> out_layers;
   std::vector<int> out_fences;
-  error = composer_->getReleaseFences(composer_callback_->GetDisplayId(),
+  error = composer_->getReleaseFences(display,
                                       &out_layers, &out_fences);
   ALOGE_IF(error != HWC::Error::None,
            "HardwareComposer::PostLayers: Failed to get release fences: %s",
@@ -527,7 +554,8 @@
   const bool display_idle = surfaces.size() == 0;
   {
     std::unique_lock<std::mutex> lock(post_thread_mutex_);
-    pending_surfaces_ = std::move(surfaces);
+    surfaces_ = std::move(surfaces);
+    surfaces_changed_ = true;
   }
 
   if (request_display_callback_ && !is_standalone_device_)
@@ -643,13 +671,11 @@
   }
 }
 
-// Waits for the next vsync and returns the timestamp of the vsync event. If
-// vsync already passed since the last call, returns the latest vsync timestamp
-// instead of blocking.
-Status<int64_t> HardwareComposer::WaitForVSync() {
-  const int64_t predicted_vsync_time =
-      last_vsync_timestamp_ +
-      display_metrics_.vsync_period_ns * vsync_prediction_interval_;
+// Sleep until the next predicted vsync, returning the predicted vsync
+// timestamp.
+Status<int64_t> HardwareComposer::WaitForPredictedVSync() {
+  const int64_t predicted_vsync_time = last_vsync_timestamp_ +
+      (target_display_->vsync_period_ns * vsync_prediction_interval_);
   const int error = SleepUntil(predicted_vsync_time);
   if (error < 0) {
     ALOGE("HardwareComposer::WaifForVSync:: Failed to sleep: %s",
@@ -695,20 +721,28 @@
       "HardwareComposer: Failed to create vsync sleep timerfd: %s",
       strerror(errno));
 
-  const int64_t ns_per_frame = display_metrics_.vsync_period_ns;
-  const int64_t photon_offset_ns = GetPosePredictionTimeOffset(ns_per_frame);
-
-  // TODO(jbates) Query vblank time from device, when such an API is available.
-  // This value (6.3%) was measured on A00 in low persistence mode.
-  int64_t vblank_ns = ns_per_frame * 63 / 1000;
-  int64_t right_eye_photon_offset_ns = (ns_per_frame - vblank_ns) / 2;
-
-  // Check property for overriding right eye offset value.
-  right_eye_photon_offset_ns =
-      property_get_int64(kRightEyeOffsetProperty, right_eye_photon_offset_ns);
-
+  struct VsyncEyeOffsets { int64_t left_ns, right_ns; };
   bool was_running = false;
 
+  auto get_vsync_eye_offsets = [this]() -> VsyncEyeOffsets {
+    VsyncEyeOffsets offsets;
+    offsets.left_ns =
+        GetPosePredictionTimeOffset(target_display_->vsync_period_ns);
+
+    // TODO(jbates) Query vblank time from device, when such an API is
+    // available. This value (6.3%) was measured on A00 in low persistence mode.
+    int64_t vblank_ns = target_display_->vsync_period_ns * 63 / 1000;
+    offsets.right_ns = (target_display_->vsync_period_ns - vblank_ns) / 2;
+
+    // Check property for overriding right eye offset value.
+    offsets.right_ns =
+        property_get_int64(kRightEyeOffsetProperty, offsets.right_ns);
+
+    return offsets;
+  };
+
+  VsyncEyeOffsets vsync_eye_offsets = get_vsync_eye_offsets();
+
   if (is_standalone_device_) {
     // First, wait until boot finishes.
     std::unique_lock<std::mutex> lock(post_thread_mutex_);
@@ -727,8 +761,8 @@
                         "Vr flinger should own the display by now.");
     post_thread_resumed_ = true;
     post_thread_ready_.notify_all();
-    OnPostThreadResumed();
-    was_running = true;
+    if (!composer_)
+      CreateComposer();
   }
 
   while (1) {
@@ -741,10 +775,8 @@
       std::unique_lock<std::mutex> lock(post_thread_mutex_);
       ALOGI("HardwareComposer::PostThread: Entering quiescent state.");
 
-      // Tear down resources if necessary.
-      if (was_running)
-        OnPostThreadPaused();
-
+      // Tear down resources.
+      OnPostThreadPaused();
       was_running = false;
       post_thread_resumed_ = false;
       post_thread_ready_.notify_all();
@@ -761,10 +793,18 @@
       ALOGI("HardwareComposer::PostThread: Exiting quiescent state.");
     }
 
-    if (!was_running) {
-      // Setup resources.
+    if (!composer_)
+      CreateComposer();
+
+    bool target_display_changed = UpdateTargetDisplay();
+    bool just_resumed_running = !was_running;
+    was_running = true;
+
+    if (target_display_changed)
+      vsync_eye_offsets = get_vsync_eye_offsets();
+
+    if (just_resumed_running) {
       OnPostThreadResumed();
-      was_running = true;
 
       // Try to setup the scheduler policy if it failed during startup. Only
       // attempt to do this on transitions from inactive to active to avoid
@@ -773,12 +813,16 @@
         thread_policy_setup =
             SetThreadPolicy("graphics:high", "/system/performance");
       }
+    }
 
+    if (target_display_changed || just_resumed_running) {
       // Initialize the last vsync timestamp with the current time. The
       // predictor below uses this time + the vsync interval in absolute time
       // units for the initial delay. Once the driver starts reporting vsync the
       // predictor will sync up with the real vsync.
       last_vsync_timestamp_ = GetSystemClockNs();
+      vsync_prediction_interval_ = 1;
+      retire_fence_fds_.clear();
     }
 
     int64_t vsync_timestamp = 0;
@@ -788,7 +832,7 @@
                    vsync_count_ + 1, last_vsync_timestamp_,
                    vsync_prediction_interval_);
 
-      auto status = WaitForVSync();
+      auto status = WaitForPredictedVSync();
       ALOGE_IF(
           !status,
           "HardwareComposer::PostThread: Failed to wait for vsync event: %s",
@@ -809,16 +853,16 @@
     if (vsync_prediction_interval_ == 1)
       ++vsync_count_;
 
-    const bool layer_config_changed = UpdateLayerConfig();
+    UpdateLayerConfig();
 
     // Publish the vsync event.
     if (vsync_ring_) {
       DvrVsync vsync;
       vsync.vsync_count = vsync_count_;
       vsync.vsync_timestamp_ns = vsync_timestamp;
-      vsync.vsync_left_eye_offset_ns = photon_offset_ns;
-      vsync.vsync_right_eye_offset_ns = right_eye_photon_offset_ns;
-      vsync.vsync_period_ns = ns_per_frame;
+      vsync.vsync_left_eye_offset_ns = vsync_eye_offsets.left_ns;
+      vsync.vsync_right_eye_offset_ns = vsync_eye_offsets.right_ns;
+      vsync.vsync_period_ns = target_display_->vsync_period_ns;
 
       vsync_ring_->Publish(vsync);
     }
@@ -832,7 +876,8 @@
       // Sleep until shortly before vsync.
       ATRACE_NAME("sleep");
 
-      const int64_t display_time_est_ns = vsync_timestamp + ns_per_frame;
+      const int64_t display_time_est_ns =
+          vsync_timestamp + target_display_->vsync_period_ns;
       const int64_t now_ns = GetSystemClockNs();
       const int64_t sleep_time_ns = display_time_est_ns - now_ns -
                                     post_thread_config_.frame_post_offset_ns;
@@ -853,11 +898,7 @@
     }
 
     {
-      auto status = composer_callback_->GetVsyncTime();
-      if (!status) {
-        ALOGE("HardwareComposer::PostThread: Failed to get VSYNC time: %s",
-              status.GetErrorMessage().c_str());
-      }
+      auto status = composer_callback_->GetVsyncTime(target_display_->id);
 
       // If we failed to read vsync there might be a problem with the driver.
       // Since there's nothing we can do just behave as though we didn't get an
@@ -884,20 +925,84 @@
       }
     }
 
-    PostLayers();
+    PostLayers(target_display_->id);
   }
 }
 
+bool HardwareComposer::UpdateTargetDisplay() {
+  bool target_display_changed = false;
+  auto displays = composer_callback_->GetDisplays();
+  if (displays.external_display_was_hotplugged) {
+    bool was_using_external_display = !target_display_->is_primary;
+    if (was_using_external_display) {
+      // The external display was hotplugged, so make sure to ignore any bad
+      // display errors as we destroy the layers.
+      for (auto& layer: layers_)
+        layer.IgnoreBadDisplayErrorsOnDestroy(true);
+    }
+
+    if (displays.external_display) {
+      // External display was connected
+      external_display_ = GetDisplayParams(composer_.get(),
+          *displays.external_display, /*is_primary*/ false);
+
+      if (property_get_bool(kUseExternalDisplayProperty, false)) {
+        ALOGI("External display connected. Switching to external display.");
+        target_display_ = &(*external_display_);
+        target_display_changed = true;
+      } else {
+        ALOGI("External display connected, but sysprop %s is unset, so"
+              " using primary display.", kUseExternalDisplayProperty);
+        if (was_using_external_display) {
+          target_display_ = &primary_display_;
+          target_display_changed = true;
+        }
+      }
+    } else {
+      // External display was disconnected
+      external_display_ = std::nullopt;
+      if (was_using_external_display) {
+        ALOGI("External display disconnected. Switching to primary display.");
+        target_display_ = &primary_display_;
+        target_display_changed = true;
+      }
+    }
+  }
+
+  if (target_display_changed) {
+    // If we're switching to the external display, turn the primary display off.
+    if (!target_display_->is_primary) {
+      EnableDisplay(primary_display_, false);
+    }
+    // If we're switching to the primary display, and the external display is
+    // still connected, turn the external display off.
+    else if (target_display_->is_primary && external_display_) {
+      EnableDisplay(*external_display_, false);
+    }
+
+    // Turn the new target display on.
+    EnableDisplay(*target_display_, true);
+
+    // When we switch displays we need to recreate all the layers, so clear the
+    // current list, which will trigger layer recreation.
+    layers_.clear();
+  }
+
+  return target_display_changed;
+}
+
 // Checks for changes in the surface stack and updates the layer config to
 // accomodate the new stack.
-bool HardwareComposer::UpdateLayerConfig() {
+void HardwareComposer::UpdateLayerConfig() {
   std::vector<std::shared_ptr<DirectDisplaySurface>> surfaces;
   {
     std::unique_lock<std::mutex> lock(post_thread_mutex_);
-    if (pending_surfaces_.empty())
-      return false;
 
-    surfaces = std::move(pending_surfaces_);
+    if (!surfaces_changed_ && (!layers_.empty() || surfaces_.empty()))
+      return;
+
+    surfaces = surfaces_;
+    surfaces_changed_ = false;
   }
 
   ATRACE_NAME("UpdateLayerConfig_HwLayers");
@@ -934,8 +1039,8 @@
       layers_.erase(search);
     } else {
       // Insert a layer for the new surface.
-      layers.emplace_back(surface, blending, display_transform_,
-                          HWC::Composition::Device, layer_index);
+      layers.emplace_back(composer_.get(), *target_display_, surface, blending,
+          HWC::Composition::Device, layer_index);
     }
 
     ALOGI_IF(
@@ -956,7 +1061,6 @@
 
   ALOGD_IF(TRACE, "HardwareComposer::UpdateLayerConfig: %zd active layers",
            layers_.size());
-  return true;
 }
 
 void HardwareComposer::SetVSyncCallback(VSyncCallback callback) {
@@ -965,15 +1069,27 @@
 
 Return<void> HardwareComposer::ComposerCallback::onHotplug(
     Hwc2::Display display, IComposerCallback::Connection conn) {
+  std::lock_guard<std::mutex> lock(mutex_);
+  ALOGI("onHotplug display=%" PRIu64 " conn=%d", display, conn);
+
+  bool is_primary = !got_first_hotplug_ || display == primary_display_.id;
+
   // Our first onHotplug callback is always for the primary display.
-  //
-  // Ignore any other hotplug callbacks since the primary display is never
-  // disconnected and we don't care about other displays.
-  if (!has_display_id_) {
+  if (!got_first_hotplug_) {
     LOG_ALWAYS_FATAL_IF(conn != IComposerCallback::Connection::CONNECTED,
         "Initial onHotplug callback should be primary display connected");
-    has_display_id_ = true;
-    display_id_ = display;
+    got_first_hotplug_ = true;
+  } else if (is_primary) {
+    ALOGE("Ignoring unexpected onHotplug() call for primary display");
+    return Void();
+  }
+
+  if (conn == IComposerCallback::Connection::CONNECTED) {
+    if (!is_primary)
+      external_display_ = DisplayInfo();
+    DisplayInfo& display_info = is_primary ?
+        primary_display_ : *external_display_;
+    display_info.id = display;
 
     std::array<char, 1024> buffer;
     snprintf(buffer.data(), buffer.size(),
@@ -983,15 +1099,20 @@
           "HardwareComposer::ComposerCallback::onHotplug: Driver supports "
           "vsync_event node for display %" PRIu64,
           display);
-      driver_vsync_event_fd_ = std::move(handle);
+      display_info.driver_vsync_event_fd = std::move(handle);
     } else {
       ALOGI(
           "HardwareComposer::ComposerCallback::onHotplug: Driver does not "
           "support vsync_event node for display %" PRIu64,
           display);
     }
+  } else if (conn == IComposerCallback::Connection::DISCONNECTED) {
+    external_display_ = std::nullopt;
   }
 
+  if (!is_primary)
+    external_display_was_hotplugged_ = true;
+
   return Void();
 }
 
@@ -1002,23 +1123,45 @@
 
 Return<void> HardwareComposer::ComposerCallback::onVsync(Hwc2::Display display,
                                                          int64_t timestamp) {
-  // Ignore any onVsync callbacks for the non-primary display.
-  if (has_display_id_ && display == display_id_) {
+  DisplayInfo* display_info = GetDisplayInfo(display);
+  if (display_info) {
     TRACE_FORMAT("vsync_callback|display=%" PRIu64 ";timestamp=%" PRId64 "|",
                  display, timestamp);
-    callback_vsync_timestamp_ = timestamp;
+    display_info->callback_vsync_timestamp = timestamp;
   }
+
   return Void();
 }
 
-Status<int64_t> HardwareComposer::ComposerCallback::GetVsyncTime() {
+HardwareComposer::ComposerCallback::Displays
+HardwareComposer::ComposerCallback::GetDisplays() {
+  std::lock_guard<std::mutex> lock(mutex_);
+  Displays displays;
+  displays.primary_display = primary_display_.id;
+  if (external_display_)
+    displays.external_display = external_display_->id;
+  if (external_display_was_hotplugged_) {
+    external_display_was_hotplugged_ = false;
+    displays.external_display_was_hotplugged = true;
+  }
+  return displays;
+}
+
+Status<int64_t> HardwareComposer::ComposerCallback::GetVsyncTime(
+    hwc2_display_t display) {
+  DisplayInfo* display_info = GetDisplayInfo(display);
+  if (!display_info) {
+    ALOGW("Attempt to get vsync time for unknown display %" PRIu64, display);
+    return ErrorStatus(EINVAL);
+  }
+
   // See if the driver supports direct vsync events.
-  LocalHandle& event_fd = driver_vsync_event_fd_;
+  LocalHandle& event_fd = display_info->driver_vsync_event_fd;
   if (!event_fd) {
     // Fall back to returning the last timestamp returned by the vsync
     // callback.
-    std::lock_guard<std::mutex> autolock(vsync_mutex_);
-    return callback_vsync_timestamp_;
+    std::lock_guard<std::mutex> autolock(mutex_);
+    return display_info->callback_vsync_timestamp;
   }
 
   // When the driver supports the vsync_event sysfs node we can use it to
@@ -1066,19 +1209,32 @@
   return {timestamp};
 }
 
-Hwc2::Composer* Layer::composer_{nullptr};
-HWCDisplayMetrics Layer::display_metrics_{0, 0, {0, 0}, 0};
-hwc2_display_t Layer::display_id_{0};
+HardwareComposer::ComposerCallback::DisplayInfo*
+HardwareComposer::ComposerCallback::GetDisplayInfo(hwc2_display_t display) {
+  if (display == primary_display_.id) {
+    return &primary_display_;
+  } else if (external_display_ && display == external_display_->id) {
+    return &(*external_display_);
+  }
+  return nullptr;
+}
 
 void Layer::Reset() {
   if (hardware_composer_layer_) {
-    composer_->destroyLayer(display_id_, hardware_composer_layer_);
+    HWC::Error error =
+        composer_->destroyLayer(display_params_.id, hardware_composer_layer_);
+    if (error != HWC::Error::None &&
+        (!ignore_bad_display_errors_on_destroy_ ||
+         error != HWC::Error::BadDisplay)) {
+      ALOGE("destroyLayer() failed for display %" PRIu64 ", layer %" PRIu64
+          ". error: %s", display_params_.id, hardware_composer_layer_,
+          error.to_string().c_str());
+    }
     hardware_composer_layer_ = 0;
   }
 
   z_order_ = 0;
   blending_ = HWC::BlendMode::None;
-  transform_ = HWC::Transform::None;
   composition_type_ = HWC::Composition::Invalid;
   target_composition_type_ = composition_type_;
   source_ = EmptyVariant{};
@@ -1086,25 +1242,29 @@
   surface_rect_functions_applied_ = false;
   pending_visibility_settings_ = true;
   cached_buffer_map_.clear();
+  ignore_bad_display_errors_on_destroy_ = false;
 }
 
-Layer::Layer(const std::shared_ptr<DirectDisplaySurface>& surface,
-             HWC::BlendMode blending, HWC::Transform transform,
-             HWC::Composition composition_type, size_t z_order)
-    : z_order_{z_order},
+Layer::Layer(Hwc2::Composer* composer, const DisplayParams& display_params,
+             const std::shared_ptr<DirectDisplaySurface>& surface,
+             HWC::BlendMode blending, HWC::Composition composition_type,
+             size_t z_order)
+    : composer_(composer),
+      display_params_(display_params),
+      z_order_{z_order},
       blending_{blending},
-      transform_{transform},
       target_composition_type_{composition_type},
       source_{SourceSurface{surface}} {
   CommonLayerSetup();
 }
 
-Layer::Layer(const std::shared_ptr<IonBuffer>& buffer, HWC::BlendMode blending,
-             HWC::Transform transform, HWC::Composition composition_type,
-             size_t z_order)
-    : z_order_{z_order},
+Layer::Layer(Hwc2::Composer* composer, const DisplayParams& display_params,
+             const std::shared_ptr<IonBuffer>& buffer, HWC::BlendMode blending,
+             HWC::Composition composition_type, size_t z_order)
+    : composer_(composer),
+      display_params_(display_params),
+      z_order_{z_order},
       blending_{blending},
-      transform_{transform},
       target_composition_type_{composition_type},
       source_{SourceBuffer{buffer}} {
   CommonLayerSetup();
@@ -1118,10 +1278,11 @@
   if (this != &other) {
     Reset();
     using std::swap;
+    swap(composer_, other.composer_);
+    swap(display_params_, other.display_params_);
     swap(hardware_composer_layer_, other.hardware_composer_layer_);
     swap(z_order_, other.z_order_);
     swap(blending_, other.blending_);
-    swap(transform_, other.transform_);
     swap(composition_type_, other.composition_type_);
     swap(target_composition_type_, other.target_composition_type_);
     swap(source_, other.source_);
@@ -1130,6 +1291,8 @@
          other.surface_rect_functions_applied_);
     swap(pending_visibility_settings_, other.pending_visibility_settings_);
     swap(cached_buffer_map_, other.cached_buffer_map_);
+    swap(ignore_bad_display_errors_on_destroy_,
+         other.ignore_bad_display_errors_on_destroy_);
   }
   return *this;
 }
@@ -1169,14 +1332,14 @@
     HWC::Error error;
 
     error = composer_->setLayerBlendMode(
-        display_id_, hardware_composer_layer_,
+        display_params_.id, hardware_composer_layer_,
         blending_.cast<Hwc2::IComposerClient::BlendMode>());
     ALOGE_IF(error != HWC::Error::None,
              "Layer::UpdateLayerSettings: Error setting layer blend mode: %s",
              error.to_string().c_str());
 
-    error = composer_->setLayerZOrder(display_id_, hardware_composer_layer_,
-                                      z_order_);
+    error = composer_->setLayerZOrder(display_params_.id,
+        hardware_composer_layer_, z_order_);
     ALOGE_IF(error != HWC::Error::None,
              "Layer::UpdateLayerSettings: Error setting z_ order: %s",
              error.to_string().c_str());
@@ -1191,28 +1354,28 @@
   // TODO(eieio): Use surface attributes or some other mechanism to control
   // the layer display frame.
   error = composer_->setLayerDisplayFrame(
-      display_id_, hardware_composer_layer_,
-      {0, 0, display_metrics_.width, display_metrics_.height});
+      display_params_.id, hardware_composer_layer_,
+      {0, 0, display_params_.width, display_params_.height});
   ALOGE_IF(error != HWC::Error::None,
            "Layer::UpdateLayerSettings: Error setting layer display frame: %s",
            error.to_string().c_str());
 
   error = composer_->setLayerVisibleRegion(
-      display_id_, hardware_composer_layer_,
-      {{0, 0, display_metrics_.width, display_metrics_.height}});
+      display_params_.id, hardware_composer_layer_,
+      {{0, 0, display_params_.width, display_params_.height}});
   ALOGE_IF(error != HWC::Error::None,
            "Layer::UpdateLayerSettings: Error setting layer visible region: %s",
            error.to_string().c_str());
 
-  error = composer_->setLayerPlaneAlpha(display_id_, hardware_composer_layer_,
-                                        1.0f);
+  error = composer_->setLayerPlaneAlpha(display_params_.id,
+      hardware_composer_layer_, 1.0f);
   ALOGE_IF(error != HWC::Error::None,
            "Layer::UpdateLayerSettings: Error setting layer plane alpha: %s",
            error.to_string().c_str());
 }
 
 void Layer::CommonLayerSetup() {
-  HWC::Error error = composer_->createLayer(display_id_,
+  HWC::Error error = composer_->createLayer(display_params_.id,
                                             &hardware_composer_layer_);
   ALOGE_IF(error != HWC::Error::None,
            "Layer::CommonLayerSetup: Failed to create layer on primary "
@@ -1257,10 +1420,10 @@
     if (composition_type_ == HWC::Composition::Invalid) {
       composition_type_ = HWC::Composition::SolidColor;
       composer_->setLayerCompositionType(
-          display_id_, hardware_composer_layer_,
+          display_params_.id, hardware_composer_layer_,
           composition_type_.cast<Hwc2::IComposerClient::Composition>());
       Hwc2::IComposerClient::Color layer_color = {0, 0, 0, 0};
-      composer_->setLayerColor(display_id_, hardware_composer_layer_,
+      composer_->setLayerColor(display_params_.id, hardware_composer_layer_,
                                layer_color);
     } else {
       // The composition type is already set. Nothing else to do until a
@@ -1270,7 +1433,7 @@
     if (composition_type_ != target_composition_type_) {
       composition_type_ = target_composition_type_;
       composer_->setLayerCompositionType(
-          display_id_, hardware_composer_layer_,
+          display_params_.id, hardware_composer_layer_,
           composition_type_.cast<Hwc2::IComposerClient::Composition>());
     }
 
@@ -1281,7 +1444,7 @@
 
     HWC::Error error{HWC::Error::None};
     error =
-        composer_->setLayerBuffer(display_id_, hardware_composer_layer_,
+        composer_->setLayerBuffer(display_params_.id, hardware_composer_layer_,
                                   slot, handle, acquire_fence_.Get());
 
     ALOGE_IF(error != HWC::Error::None,
@@ -1291,7 +1454,7 @@
     if (!surface_rect_functions_applied_) {
       const float float_right = right;
       const float float_bottom = bottom;
-      error = composer_->setLayerSourceCrop(display_id_,
+      error = composer_->setLayerSourceCrop(display_params_.id,
                                             hardware_composer_layer_,
                                             {0, 0, float_right, float_bottom});
 
diff --git a/libs/vr/libvrflinger/hardware_composer.h b/libs/vr/libvrflinger/hardware_composer.h
index 4a503f8..1d8d463 100644
--- a/libs/vr/libvrflinger/hardware_composer.h
+++ b/libs/vr/libvrflinger/hardware_composer.h
@@ -13,6 +13,7 @@
 #include <condition_variable>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <thread>
 #include <tuple>
 #include <vector>
@@ -35,16 +36,19 @@
 namespace android {
 namespace dvr {
 
-// Basic display metrics for physical displays. Dimensions and densities are
-// relative to the physical display orientation, which may be different from the
-// logical display orientation exposed to applications.
-struct HWCDisplayMetrics {
+// Basic display metrics for physical displays.
+struct DisplayParams {
+  hwc2_display_t id;
+  bool is_primary;
+
   int width;
   int height;
+
   struct {
     int x;
     int y;
   } dpi;
+
   int vsync_period_ns;
 };
 
@@ -58,26 +62,29 @@
   // automatically handles ACQUIRE/RELEASE phases for the surface's buffer train
   // every frame.
   //
+  // |composer| The composer instance.
+  // |display_params| Info about the display to use.
   // |blending| receives HWC_BLENDING_* values.
-  // |transform| receives HWC_TRANSFORM_* values.
   // |composition_type| receives either HWC_FRAMEBUFFER for most layers or
   // HWC_FRAMEBUFFER_TARGET (unless you know what you are doing).
   // |index| is the index of this surface in the DirectDisplaySurface array.
-  Layer(const std::shared_ptr<DirectDisplaySurface>& surface,
-        HWC::BlendMode blending, HWC::Transform transform,
-        HWC::Composition composition_type, size_t z_roder);
+  Layer(Hwc2::Composer* composer, const DisplayParams& display_params,
+        const std::shared_ptr<DirectDisplaySurface>& surface,
+        HWC::BlendMode blending, HWC::Composition composition_type,
+        size_t z_order);
 
   // Sets up the layer to use a direct buffer as its content source. No special
   // handling of the buffer is performed; responsibility for updating or
   // changing the buffer each frame is on the caller.
   //
+  // |composer| The composer instance.
+  // |display_params| Info about the display to use.
   // |blending| receives HWC_BLENDING_* values.
-  // |transform| receives HWC_TRANSFORM_* values.
   // |composition_type| receives either HWC_FRAMEBUFFER for most layers or
   // HWC_FRAMEBUFFER_TARGET (unless you know what you are doing).
-  Layer(const std::shared_ptr<IonBuffer>& buffer, HWC::BlendMode blending,
-        HWC::Transform transform, HWC::Composition composition_type,
-        size_t z_order);
+  Layer(Hwc2::Composer* composer, const DisplayParams& display_params,
+        const std::shared_ptr<IonBuffer>& buffer, HWC::BlendMode blending,
+        HWC::Composition composition_type, size_t z_order);
 
   Layer(Layer&&);
   Layer& operator=(Layer&&);
@@ -144,17 +151,8 @@
   }
   bool operator<(int surface_id) const { return GetSurfaceId() < surface_id; }
 
-  // Sets the composer instance used by all Layer instances.
-  static void SetComposer(Hwc2::Composer* composer) { composer_ = composer; }
-
-  // Sets the display metrics used by all Layer instances.
-  static void SetDisplayMetrics(HWCDisplayMetrics display_metrics) {
-    display_metrics_ = display_metrics;
-  }
-
-  // Sets the display id used by all Layer instances.
-  static void SetDisplayId(hwc2_display_t display_id) {
-    display_id_ = display_id;
+  void IgnoreBadDisplayErrorsOnDestroy(bool ignore) {
+    ignore_bad_display_errors_on_destroy_ = ignore;
   }
 
  private:
@@ -174,21 +172,11 @@
   // associated and always returns false.
   bool CheckAndUpdateCachedBuffer(std::size_t slot, int buffer_id);
 
-  // Composer instance shared by all instances of Layer. This must be set
-  // whenever a new instance of the Composer is created. This may be set to
-  // nullptr as long as there are no instances of Layer that might need to use
-  // it.
-  static Hwc2::Composer* composer_;
+  // Composer instance.
+  Hwc2::Composer* composer_ = nullptr;
 
-  // Display metrics shared by all instances of Layer. This must be set at least
-  // once during VrFlinger initialization and is expected to remain constant
-  // thereafter.
-  static HWCDisplayMetrics display_metrics_;
-
-  // Id of the primary display. Shared by all instances of Layer. This must be
-  // set whenever the primary display id changes. This can be left unset as long
-  // as there are no instances of Layer that might need to use it.
-  static hwc2_display_t display_id_;
+  // Parameters of the display to use for this layer.
+  DisplayParams display_params_;
 
   // The hardware composer layer and metrics to use during the prepare cycle.
   hwc2_layer_t hardware_composer_layer_ = 0;
@@ -197,7 +185,6 @@
   // Prepare phase.
   size_t z_order_ = 0;
   HWC::BlendMode blending_ = HWC::BlendMode::None;
-  HWC::Transform transform_ = HWC::Transform::None;
   HWC::Composition composition_type_ = HWC::Composition::Invalid;
   HWC::Composition target_composition_type_ = HWC::Composition::Device;
 
@@ -293,6 +280,12 @@
   // importing a buffer HWC already knows about.
   std::map<std::size_t, int> cached_buffer_map_;
 
+  // When calling destroyLayer() on an external display that's been removed we
+  // typically get HWC2_ERROR_BAD_DISPLAY errors. If
+  // ignore_bad_display_errors_on_destroy_ is true, don't log the bad display
+  // errors, since they're expected.
+  bool ignore_bad_display_errors_on_destroy_ = false;
+
   Layer(const Layer&) = delete;
   void operator=(const Layer&) = delete;
 };
@@ -330,22 +323,12 @@
   // Called on a binder thread.
   void OnBootFinished();
 
-  // Get the HMD display metrics for the current display.
-  display::Metrics GetHmdDisplayMetrics() const;
-
   std::string Dump();
 
   void SetVSyncCallback(VSyncCallback callback);
 
-  // Metrics of the logical display, which is always landscape.
-  int DisplayWidth() const { return display_metrics_.width; }
-  int DisplayHeight() const { return display_metrics_.height; }
-  HWCDisplayMetrics display_metrics() const { return display_metrics_; }
-
-  // Metrics of the native display, which depends on the specific hardware
-  // implementation of the display.
-  HWCDisplayMetrics native_display_metrics() const {
-    return native_display_metrics_;
+  const DisplayParams& GetPrimaryDisplayParams() const {
+    return primary_display_;
   }
 
   // Sets the display surfaces to compose the hardware layer stack.
@@ -356,16 +339,16 @@
   void OnDeletedGlobalBuffer(DvrGlobalBufferKey key);
 
  private:
-  HWC::Error GetDisplayAttribute(Hwc2::Composer* composer,
-                                 hwc2_display_t display, hwc2_config_t config,
-                                 hwc2_attribute_t attributes,
-                                 int32_t* out_value) const;
-  HWC::Error GetDisplayMetrics(Hwc2::Composer* composer, hwc2_display_t display,
-                               hwc2_config_t config,
-                               HWCDisplayMetrics* out_metrics) const;
+  DisplayParams GetDisplayParams(Hwc2::Composer* composer,
+      hwc2_display_t display, bool is_primary);
 
-  HWC::Error EnableVsync(bool enabled);
-  HWC::Error SetPowerMode(bool active);
+  // Turn display vsync on/off. Returns true on success, false on failure.
+  bool EnableVsync(const DisplayParams& display, bool enabled);
+  // Turn display power on/off. Returns true on success, false on failure.
+  bool SetPowerMode(const DisplayParams& display, bool active);
+  // Convenience function to turn a display on/off. Turns both power and vsync
+  // on/off. Returns true on success, false on failure.
+  bool EnableDisplay(const DisplayParams& display, bool enabled);
 
   class ComposerCallback : public Hwc2::IComposerCallback {
    public:
@@ -376,22 +359,38 @@
     hardware::Return<void> onVsync(Hwc2::Display display,
                                    int64_t timestamp) override;
 
-    bool HasDisplayId() { return has_display_id_; }
-    hwc2_display_t GetDisplayId() { return display_id_; }
-    pdx::Status<int64_t> GetVsyncTime();
+    bool GotFirstHotplug() { return got_first_hotplug_; }
+
+    struct Displays {
+      hwc2_display_t primary_display = 0;
+      std::optional<hwc2_display_t> external_display;
+      bool external_display_was_hotplugged = false;
+    };
+
+    Displays GetDisplays();
+    pdx::Status<int64_t> GetVsyncTime(hwc2_display_t display);
 
    private:
-    std::mutex vsync_mutex_;
-    bool has_display_id_ = false;
-    hwc2_display_t display_id_;
-    pdx::LocalHandle driver_vsync_event_fd_;
-    int64_t callback_vsync_timestamp_{0};
+    struct DisplayInfo {
+      hwc2_display_t id = 0;
+      pdx::LocalHandle driver_vsync_event_fd;
+      int64_t callback_vsync_timestamp{0};
+    };
+
+    DisplayInfo* GetDisplayInfo(hwc2_display_t display);
+
+    std::mutex mutex_;
+
+    bool got_first_hotplug_ = false;
+    DisplayInfo primary_display_;
+    std::optional<DisplayInfo> external_display_;
+    bool external_display_was_hotplugged_ = false;
   };
 
   HWC::Error Validate(hwc2_display_t display);
   HWC::Error Present(hwc2_display_t display);
 
-  void PostLayers();
+  void PostLayers(hwc2_display_t display);
   void PostThread();
 
   // The post thread has two controlling states:
@@ -419,16 +418,24 @@
   int PostThreadPollInterruptible(const pdx::LocalHandle& event_fd,
                                   int requested_events, int timeout_ms);
 
-  // WaitForVSync and SleepUntil are blocking calls made on the post thread that
-  // can be interrupted by a control thread. If interrupted, these calls return
-  // kPostThreadInterrupted.
+  // WaitForPredictedVSync and SleepUntil are blocking calls made on the post
+  // thread that can be interrupted by a control thread. If interrupted, these
+  // calls return kPostThreadInterrupted.
   int ReadWaitPPState();
-  pdx::Status<int64_t> WaitForVSync();
+  pdx::Status<int64_t> WaitForPredictedVSync();
   int SleepUntil(int64_t wakeup_timestamp);
 
+  // Initialize any newly connected displays, and set target_display_ to the
+  // display we should render to. Returns true if target_display_
+  // changed. Called only from the post thread.
+  bool UpdateTargetDisplay();
+
   // Reconfigures the layer stack if the display surfaces changed since the last
   // frame. Called only from the post thread.
-  bool UpdateLayerConfig();
+  void UpdateLayerConfig();
+
+  // Called on the post thread to create the Composer instance.
+  void CreateComposer();
 
   // Called on the post thread when the post thread is resumed.
   void OnPostThreadResumed();
@@ -459,18 +466,19 @@
   sp<ComposerCallback> composer_callback_;
   RequestDisplayCallback request_display_callback_;
 
-  // Display metrics of the physical display.
-  HWCDisplayMetrics native_display_metrics_;
-  // Display metrics of the logical display, adjusted so that orientation is
-  // landscape.
-  HWCDisplayMetrics display_metrics_;
-  // Transform required to get from native to logical display orientation.
-  HWC::Transform display_transform_ = HWC::Transform::None;
+  DisplayParams primary_display_;
+  std::optional<DisplayParams> external_display_;
+  DisplayParams* target_display_ = &primary_display_;
 
-  // Pending surface list. Set by the display service when DirectSurfaces are
-  // added, removed, or change visibility. Written by the message dispatch
-  // thread and read by the post thread.
-  std::vector<std::shared_ptr<DirectDisplaySurface>> pending_surfaces_;
+  // The list of surfaces we should draw. Set by the display service when
+  // DirectSurfaces are added, removed, or change visibility. Written by the
+  // message dispatch thread and read by the post thread.
+  std::vector<std::shared_ptr<DirectDisplaySurface>> surfaces_;
+  // Set to true by the dispatch thread whenever surfaces_ changes. Set to false
+  // by the post thread when the new list of surfaces is processed.
+  bool surfaces_changed_ = false;
+
+  std::vector<std::shared_ptr<DirectDisplaySurface>> current_surfaces_;
 
   // Layer set for handling buffer flow into hardware composer layers. This
   // vector must be sorted by surface_id in ascending order.