Added IECoreGL::Selector::IDSelect fallback for GLSL < 330.

include/IECoreGL/Selector.h

@@ -73,7 +73,10 @@ class Selector : boost::noncopyable
 			OcclusionQuery,
 			/// Renders each object to an offscreen framebuffer using a
 			/// unique colour per object. Can therefore only select the
-			/// frontmost objects, but does provide accurate depth information. 
+			/// frontmost objects, but does provide accurate depth information.
+			/// Note that this mode is currently only supported for GLSL
+			/// versions 330 and up - lesser versions will fall back to using
+			/// the GLSelect mode.
 			IDRender
 		};
 

src/IECoreGL/Selector.cpp

@@ -52,6 +52,7 @@
 #include "IECoreGL/Primitive.h"
 #include "IECoreGL/ShaderLoader.h"
 #include "IECoreGL/TextureLoader.h"
+#include "IECoreGL/IECoreGL.h"
 
 using namespace IECoreGL;
 
@@ -100,6 +101,13 @@ class Selector::Implementation : public IECore::RefCounted
 			glMultMatrixd( projectionMatrix );
 			glMatrixMode( GL_MODELVIEW );
 
+			// fall back to GLSelect mode if we can't
+			// support IDRender mode.
+			if( m_mode == IDRender && glslVersion() < 330 )
+			{
+				m_mode = GLSelect;
+			}
+
 			switch( m_mode )
 			{
 				case GLSelect :