SF: tidy comments for luma sampling.

Tidying of const, comment and one internal fn name for
Region Luma sampling.

Test: libgui_test --gtest_filter="RegionSamp*"

Change-Id: I46895c8ed5b2e2045d7ce7444085585b62b5ab6e
diff --git a/services/surfaceflinger/RegionSamplingThread.cpp b/services/surfaceflinger/RegionSamplingThread.cpp
index cbc7ada..bd8548c 100644
--- a/services/surfaceflinger/RegionSamplingThread.cpp
+++ b/services/surfaceflinger/RegionSamplingThread.cpp
@@ -119,8 +119,9 @@
 }
 } // anonymous namespace
 
-std::vector<float> sampleBuffer(const sp<GraphicBuffer>& buffer, const Point& leftTop,
-                                const std::vector<RegionSamplingThread::Descriptor>& descriptors) {
+std::vector<float> RegionSamplingThread::sampleBuffer(
+        const sp<GraphicBuffer>& buffer, const Point& leftTop,
+        const std::vector<RegionSamplingThread::Descriptor>& descriptors) {
     void* data_raw = nullptr;
     buffer->lock(GRALLOC_USAGE_SW_READ_OFTEN, &data_raw);
     std::shared_ptr<uint32_t> data(reinterpret_cast<uint32_t*>(data_raw),
@@ -150,7 +151,7 @@
         descriptors.emplace_back(descriptor);
     }
 
-    Rect sampledArea = sampleRegion.bounds();
+    const Rect sampledArea = sampleRegion.bounds();
 
     sp<const DisplayDevice> device = mFlinger.getDefaultDisplayDevice();
     DisplayRenderArea renderArea(device, sampledArea, sampledArea.getWidth(),
@@ -174,8 +175,8 @@
             }
 
             // Compute the layer's position on the screen
-            Rect bounds = Rect(layer->getBounds());
-            ui::Transform transform = layer->getTransform();
+            const Rect bounds = Rect(layer->getBounds());
+            const ui::Transform transform = layer->getTransform();
             constexpr bool roundOutwards = true;
             Rect transformed = transform.transform(bounds, roundOutwards);
 
@@ -215,7 +216,7 @@
     //
     // To avoid this, we drop the mutex while we call into SF.
     mMutex.unlock();
-    mFlinger.captureScreenCore(renderArea, traverseLayers, buffer, false);
+    mFlinger.captureScreenCommon(renderArea, traverseLayers, buffer, false);
     mMutex.lock();
 
     std::vector<Descriptor> activeDescriptors;
@@ -229,6 +230,8 @@
     std::vector<float> lumas = sampleBuffer(buffer, sampledArea.leftTop(), activeDescriptors);
 
     if (lumas.size() != activeDescriptors.size()) {
+        ALOGW("collected %zu median luma values for %zu descriptors", lumas.size(),
+              activeDescriptors.size());
         return;
     }
 
diff --git a/services/surfaceflinger/RegionSamplingThread.h b/services/surfaceflinger/RegionSamplingThread.h
index bf59007..ab06513 100644
--- a/services/surfaceflinger/RegionSamplingThread.h
+++ b/services/surfaceflinger/RegionSamplingThread.h
@@ -38,11 +38,16 @@
     explicit RegionSamplingThread(SurfaceFlinger& flinger);
     ~RegionSamplingThread();
 
+    // Add a listener to receive luma notifications. The luma reported via listener will
+    // report the median luma for the layers under the stopLayerHandle, in the samplingArea region.
     void addListener(const Rect& samplingArea, const sp<IBinder>& stopLayerHandle,
                      const sp<IRegionSamplingListener>& listener);
+    // Remove the listener to stop receiving median luma notifications.
     void removeListener(const sp<IRegionSamplingListener>& listener);
+    // Instruct the thread to perform a median luma sampling on the layers.
     void sampleNow();
 
+private:
     struct Descriptor {
         Rect area = Rect::EMPTY_RECT;
         wp<Layer> stopLayer;
@@ -54,8 +59,10 @@
             return std::hash<IBinder*>()(p.unsafe_get());
         }
     };
+    std::vector<float> sampleBuffer(
+            const sp<GraphicBuffer>& buffer, const Point& leftTop,
+            const std::vector<RegionSamplingThread::Descriptor>& descriptors);
 
-private:
     void binderDied(const wp<IBinder>& who) override;
 
     void captureSample() REQUIRES(mMutex);
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index df558e5..a59d45a 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -5485,13 +5485,13 @@
                                              static_cast<android_pixel_format>(reqPixelFormat), 1,
                                              usage, "screenshot");
 
-    return captureScreenCore(renderArea, traverseLayers, *outBuffer, useIdentityTransform);
+    return captureScreenCommon(renderArea, traverseLayers, *outBuffer, useIdentityTransform);
 }
 
-status_t SurfaceFlinger::captureScreenCore(RenderArea& renderArea,
-                                           TraverseLayersFunction traverseLayers,
-                                           const sp<GraphicBuffer>& buffer,
-                                           bool useIdentityTransform) {
+status_t SurfaceFlinger::captureScreenCommon(RenderArea& renderArea,
+                                             TraverseLayersFunction traverseLayers,
+                                             const sp<GraphicBuffer>& buffer,
+                                             bool useIdentityTransform) {
     // This mutex protects syncFd and captureResult for communication of the return values from the
     // main thread back to this Binder thread
     std::mutex captureMutex;
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 31b4fb6..deb7870 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -635,8 +635,8 @@
     status_t captureScreenCommon(RenderArea& renderArea, TraverseLayersFunction traverseLayers,
                                  sp<GraphicBuffer>* outBuffer, const ui::PixelFormat reqPixelFormat,
                                  bool useIdentityTransform);
-    status_t captureScreenCore(RenderArea& renderArea, TraverseLayersFunction traverseLayers,
-                               const sp<GraphicBuffer>& buffer, bool useIdentityTransform);
+    status_t captureScreenCommon(RenderArea& renderArea, TraverseLayersFunction traverseLayers,
+                                 const sp<GraphicBuffer>& buffer, bool useIdentityTransform);
     status_t captureScreenImplLocked(const RenderArea& renderArea,
                                      TraverseLayersFunction traverseLayers,
                                      ANativeWindowBuffer* buffer, bool useIdentityTransform,