Add some comments.

Also, minor tweak to SurfaceTextureLayer.

Change-Id: If616d5ee4e8226dd0e16c5dbb0e0f80db553110e

6 files changed, 75 insertions, 9 deletions

diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index 8c2dade..f94a9ba 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -125,6 +125,22 @@ void Layer::setName(const String8& name) {
 
 sp<ISurface> Layer::createSurface()
 {
+    /*
+     * This class provides an implementation of BnSurface (the "native" or
+     * "remote" side of the Binder IPC interface ISurface), and mixes in
+     * LayerCleaner to ensure that mFlinger->onLayerDestroyed() is called for
+     * this layer when the BSurface is destroyed.
+     *
+     * The idea is to provide a handle to the Layer through ISurface that
+     * is cleaned up automatically when the last reference to the ISurface
+     * goes away.  (The references will be held on the "proxy" side, while
+     * the Layer exists on the "native" side.)
+     *
+     * The Layer has a reference to an instance of SurfaceFlinger's variant
+     * of GLConsumer, which holds a reference to the BufferQueue.  The
+     * getSurfaceTexture() call returns a Binder interface reference for
+     * the producer interface of the buffer queue associated with the Layer.
+     */
     class BSurface : public BnSurface, public LayerCleaner {
         wp<const Layer> mOwner;
         virtual sp<IGraphicBufferProducer> getSurfaceTexture() const {
diff --git a/services/surfaceflinger/Layer.h b/services/surfaceflinger/Layer.h
index 2d4afc4..ef829ed 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -47,11 +47,19 @@ class GLExtensions;
 
 // ---------------------------------------------------------------------------
 
+/*
+ * The Layer class is essentially a LayerBase combined with a BufferQueue.
+ * A new BufferQueue and a new SurfaceFlingerConsumer are created when the
+ * Layer is first referenced.
+ *
+ * This also implements onFrameAvailable(), which notifies SurfaceFlinger
+ * that new data has arrived.
+ */
 class Layer : public LayerBaseClient,
               public SurfaceFlingerConsumer::FrameAvailableListener
 {
 public:
-            Layer(SurfaceFlinger* flinger, const sp<Client>& client);
+    Layer(SurfaceFlinger* flinger, const sp<Client>& client);
     virtual ~Layer();
 
     virtual const char* getTypeId() const { return "Layer"; }
@@ -102,8 +110,9 @@ protected:
     virtual void clearStats();
 
 private:
-    friend class SurfaceTextureLayer;
+    // Creates an instance of ISurface for this Layer.
     virtual sp<ISurface> createSurface();
+
     uint32_t getEffectiveUsage(uint32_t usage) const;
     bool isCropped() const;
     Rect computeBufferCrop() const;
diff --git a/services/surfaceflinger/LayerBase.h b/services/surfaceflinger/LayerBase.h
index 7a9471e..47473e7 100644
--- a/services/surfaceflinger/LayerBase.h
+++ b/services/surfaceflinger/LayerBase.h
@@ -49,6 +49,18 @@ class SurfaceFlinger;
 
 // ---------------------------------------------------------------------------
 
+/*
+ * Layers are rectangular graphic entities, internal to SurfaceFlinger.
+ * They have properties including width, height, Z-depth, and 2D
+ * transformations (chiefly translation and 90-degree rotations).
+ *
+ * Layers are organized into "layer stacks".  Each layer is a member of
+ * exactly one layer stack, identified by an integer in Layer::State.  A
+ * given layer stack may appear on more than one display.
+ *
+ * Notable subclasses (below LayerBaseClient) include Layer, LayerDim, and
+ * LayerScreenshot.
+ */
 class LayerBase : virtual public RefBase
 {
     static int32_t sSequence;
@@ -308,16 +320,27 @@ private:
 
 // ---------------------------------------------------------------------------
 
+/*
+ * This adds some additional fields and methods to support some Binder IPC
+ * interactions.  In particular, the LayerBaseClient's lifetime can be
+ * managed by references to an ISurface object in another process.
+ */
 class LayerBaseClient : public LayerBase
 {
 public:
-            LayerBaseClient(SurfaceFlinger* flinger, const sp<Client>& client);
+    LayerBaseClient(SurfaceFlinger* flinger, const sp<Client>& client);
+
+    virtual ~LayerBaseClient();
 
-            virtual ~LayerBaseClient();
+    // Creates an ISurface associated with this object.  This may only be
+    // called once (see also getSurfaceBinder()).
+    sp<ISurface> getSurface();
 
-            sp<ISurface> getSurface();
-            wp<IBinder> getSurfaceBinder() const;
-            virtual wp<IBinder> getSurfaceTextureBinder() const;
+    // Returns the Binder object for the ISurface associated with
+    // this object.
+    wp<IBinder> getSurfaceBinder() const;
+
+    virtual wp<IBinder> getSurfaceTextureBinder() const;
 
     virtual sp<LayerBaseClient> getLayerBaseClient() const {
         return const_cast<LayerBaseClient*>(this); }
@@ -330,6 +353,10 @@ protected:
     virtual void dump(String8& result, char* scratch, size_t size) const;
     virtual void shortDump(String8& result, char* scratch, size_t size) const;
 
+    /*
+     * Trivial class, used to ensure that mFlinger->onLayerDestroyed(mLayer)
+     * is called.
+     */
     class LayerCleaner {
         sp<SurfaceFlinger> mFlinger;
         wp<LayerBaseClient> mLayer;
@@ -344,8 +371,13 @@ private:
     virtual sp<ISurface> createSurface();
 
     mutable Mutex mLock;
+
+    // Set to true if an ISurface has been associated with this object.
     mutable bool mHasSurface;
+
+    // The ISurface's Binder object, set by getSurface().
     wp<IBinder> mClientSurfaceBinder;
+
     const wp<Client> mClientRef;
     // only read
     const uint32_t mIdentity;
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index f0e5719..46476f9 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -575,13 +575,18 @@ bool SurfaceFlinger::authenticateSurfaceTexture(
     Mutex::Autolock _l(mStateLock);
     sp<IBinder> surfaceTextureBinder(bufferProducer->asBinder());
 
-    // Check the visible layer list for the ISurface
+    // We want to determine whether the IGraphicBufferProducer was created by
+    // SurfaceFlinger.  Check to see if we can find it in the layer list.
     const LayerVector& currentLayers = mCurrentState.layersSortedByZ;
     size_t count = currentLayers.size();
     for (size_t i=0 ; i<count ; i++) {
         const sp<LayerBase>& layer(currentLayers[i]);
         sp<LayerBaseClient> lbc(layer->getLayerBaseClient());
         if (lbc != NULL) {
+            // If this is an instance of Layer (as opposed to, say, LayerDim),
+            // we will get the consumer interface of SurfaceFlingerConsumer's
+            // BufferQueue.  If it's the same Binder object as the graphic
+            // buffer producer interface, return success.
             wp<IBinder> lbcBinder = lbc->getSurfaceTextureBinder();
             if (lbcBinder == surfaceTextureBinder) {
                 return true;
diff --git a/services/surfaceflinger/SurfaceTextureLayer.cpp b/services/surfaceflinger/SurfaceTextureLayer.cpp
index 0b638b4..395c8c8 100644
--- a/services/surfaceflinger/SurfaceTextureLayer.cpp
+++ b/services/surfaceflinger/SurfaceTextureLayer.cpp
@@ -20,7 +20,6 @@
 
 #include <utils/Errors.h>
 
-#include "Layer.h"
 #include "SurfaceTextureLayer.h"
 
 namespace android {
diff --git a/services/surfaceflinger/SurfaceTextureLayer.h b/services/surfaceflinger/SurfaceTextureLayer.h
index 8baa8d2..a75ccf4 100644
--- a/services/surfaceflinger/SurfaceTextureLayer.h
+++ b/services/surfaceflinger/SurfaceTextureLayer.h
@@ -29,12 +29,17 @@ namespace android {
 
 class Layer;
 
+/*
+ * This is a thin wrapper around BufferQueue, used by the Layer class.
+ */
 class SurfaceTextureLayer : public BufferQueue
 {
 public:
     SurfaceTextureLayer();
     ~SurfaceTextureLayer();
 
+    // After calling the superclass connect(), set or clear synchronous
+    // mode appropriately for the specified API.
     virtual status_t connect(int api, QueueBufferOutput* output);
 };