From 75fd039dba9cc049e8a37b2c8dfa84ea8a3b1002 Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Wed, 24 Jul 2013 13:02:32 +0000
Subject: [PATCH] Added GL2Extensions::isDrawBuffersSupported() and usage of
 this in FrameBufferObject.cpp to prevent crash under GLES2 when users attempt
 to use MRT when it's not supported

---
 include/osg/GL2Extensions     | 2 ++
 src/osg/FrameBufferObject.cpp | 8 ++++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/osg/GL2Extensions b/include/osg/GL2Extensions
index 39d2c3545..0c4a1a699 100644
--- a/include/osg/GL2Extensions
+++ b/include/osg/GL2Extensions
@@ -530,6 +530,8 @@ class OSG_EXPORT GL2Extensions : public osg::Referenced
         void setShaderAtomicCounterSupported(bool flag) { _isShaderAtomicCountersSupported = flag; }
         bool isShaderAtomicCounterSupported() const {return _isShaderAtomicCountersSupported; }
 
+        bool isDrawBuffersSupported() const { return _glDrawBuffers!=0; }
+
         /** Function to call to get the extension of a specified context.
           * If the Exentsion object for that context has not yet been created then
           * and the 'createIfNotInitalized' flag been set to false then returns NULL.
diff --git a/src/osg/FrameBufferObject.cpp b/src/osg/FrameBufferObject.cpp
index 68c755a8c..ec570d14e 100644
--- a/src/osg/FrameBufferObject.cpp
+++ b/src/osg/FrameBufferObject.cpp
@@ -916,10 +916,14 @@ void FrameBufferObject::apply(State &state, BindTarget target) const
     if (_drawBuffers.size() > 0)
     {
         GL2Extensions *gl2e = GL2Extensions::Get(state.getContextID(), true );
-        if (gl2e)
+        if (gl2e && gl2e->isDrawBuffersSupported())
         {
             gl2e->glDrawBuffers(_drawBuffers.size(), &(_drawBuffers[0]));
         }
+        else
+        {
+            OSG_WARN <<"Warning: FrameBufferObject: could not set draw buffers, glDrawBuffers is not supported!" << std::endl;
+        }
     }
 
     if (dirtyAttachmentList)
@@ -939,7 +943,7 @@ void FrameBufferObject::apply(State &state, BindTarget target) const
                     {
                         OSG_WARN <<
                             "Warning: FrameBufferObject: could not attach PACKED_DEPTH_STENCIL_BUFFER, "
-                            "EXT_packed_depth_stencil is not supported !" << std::endl;
+                            "EXT_packed_depth_stencil is not supported!" << std::endl;
                     }
                     break;