GL3: Implement RAMPreferred

--HG--
branch : opengl3

code/nel/src/3d/driver/opengl3/driver_opengl_vertex_buffer.cpp

@@ -148,7 +148,12 @@ void *CVertexBufferGL::lock()
 	case CVertexBuffer::RAMVolatile:
 		m_VertexPtr = nglMapBufferRange(GL_ARRAY_BUFFER, 0, size, GL_MAP_WRITE_BIT | GL_MAP_INVALIDATE_BUFFER_BIT);
 		break;
+	case CVertexBuffer::RAMPreferred:
+		// m_VertexPtr = nglMapBufferRange(GL_ARRAY_BUFFER, 0, size, GL_MAP_WRITE_BIT | GL_MAP_READ_BIT);
+		m_VertexPtr = nglMapBuffer(GL_ARRAY_BUFFER, GL_READ_WRITE);
+		break;
 	default:
+		// m_VertexPtr = nglMapBufferRange(GL_ARRAY_BUFFER, 0, size, GL_MAP_WRITE_BIT);
 		m_VertexPtr = nglMapBuffer(GL_ARRAY_BUFFER, GL_WRITE_ONLY);
 		break;
 	}