From fb410365ca67d36d4c81d7826712c6a05437612f Mon Sep 17 00:00:00 2001
From: Mathias Agopian <mathias@google.com>
Date: Tue, 15 Nov 2011 21:27:52 -0800
Subject: [PATCH] improve hw composer documentation

Change-Id: I39363e37417991b9853309154d6691240e706acf
---
 include/hardware/hwcomposer.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index 0fa3512f..a17f3e43 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -287,6 +287,11 @@ typedef struct hwc_composer_device {
      * entire composition has been handled by SurfaceFlinger with OpenGL ES.
      * In this case, (*set)() behaves just like eglSwapBuffers().
      *
+     * IMPORTANT NOTE: there is an implicit layer containing opaque black
+     * pixels behind all the layers in the list.
+     * It is the responsibility of the hwcomposer module to make
+     * sure black pixels are output (or blended from).
+     *
      * returns: 0 on success. An negative error code on error:
      *    HWC_EGL_ERROR: eglGetError() will provide the proper error code
      *    Another code for non EGL errors.