diff --git a/services/surfaceflinger/RenderArea.h b/services/surfaceflinger/RenderArea.h
index e38f462..9920f0a 100644
--- a/services/surfaceflinger/RenderArea.h
+++ b/services/surfaceflinger/RenderArea.h
@@ -8,8 +8,13 @@
 
 namespace android {
 
+// RenderArea describes a rectangular area that layers can be rendered to.
+//
+// There is a logical render area and a physical render area.  When a layer is
+// rendered to the render area, it is first transformed and clipped to the logical
+// render area.  The transformed and clipped layer is then projected onto the
+// physical render area.
 class RenderArea {
-
 public:
     enum class CaptureFill {CLEAR, OPAQUE};
 
@@ -20,23 +25,51 @@
 
     virtual ~RenderArea() = default;
 
-    virtual const ui::Transform& getTransform() const = 0;
-    virtual Rect getBounds() const = 0;
-    virtual int getHeight() const = 0;
-    virtual int getWidth() const = 0;
-    virtual bool isSecure() const = 0;
-    virtual bool needsFiltering() const = 0;
-    virtual Rect getSourceCrop() const = 0;
-
+    // Invoke drawLayers to render layers into the render area.
     virtual void render(std::function<void()> drawLayers) { drawLayers(); }
 
-    int getReqHeight() const { return mReqHeight; };
-    int getReqWidth() const { return mReqWidth; };
-    ui::Transform::orientation_flags getRotationFlags() const { return mRotationFlags; };
-    status_t updateDimensions(int displayRotation);
+    // Returns true if the render area is secure.  A secure layer should be
+    // blacked out / skipped when rendered to an insecure render area.
+    virtual bool isSecure() const = 0;
 
+    // Returns true if the otherwise disabled layer filtering should be
+    // enabled when rendering to this render area.
+    virtual bool needsFiltering() const = 0;
+
+    // Returns the transform to be applied on layers to transform them into
+    // the logical render area.
+    virtual const ui::Transform& getTransform() const = 0;
+
+    // Returns the size of the logical render area.  Layers are clipped to the
+    // logical render area.
+    virtual int getWidth() const = 0;
+    virtual int getHeight() const = 0;
+    virtual Rect getBounds() const = 0;
+
+    // Returns the source crop of the render area.  The source crop defines
+    // how layers are projected from the logical render area onto the physical
+    // render area.  It can be larger than the logical render area.  It can
+    // also be optionally rotated.
+    //
+    // Layers are first clipped to the source crop (in addition to being
+    // clipped to the logical render area already).  The source crop and the
+    // layers are then rotated around the center of the source crop, and
+    // scaled to the physical render area linearly.
+    virtual Rect getSourceCrop() const = 0;
+
+    // Returns the rotation of the source crop and the layers.
+    ui::Transform::orientation_flags getRotationFlags() const { return mRotationFlags; };
+
+    // Returns the size of the physical render area.
+    int getReqWidth() const { return mReqWidth; };
+    int getReqHeight() const { return mReqHeight; };
+
+    // Returns the fill color of the physical render area.  Regions not
+    // covered by any rendered layer should be filled with this color.
     CaptureFill getCaptureFill() const { return mCaptureFill; };
 
+    status_t updateDimensions(int displayRotation);
+
 private:
     uint32_t mReqHeight;
     uint32_t mReqWidth;