why cause rhe folllowing result?

[4129qq]

MPGeometry* geom= dynamic_cast<MPGeometry*>( geode->getDrawable(0) );
std::string vs = Stringify()
<< "varying vec4 oe_layer_texc; \n"
<< "void my_filter_vertex(inout vec4 VertexMODEL) \n"
<< "{ \n"
<< " oe_layer_texc = gl_MultiTexCoord0; \n"
<<"} \n";
std::string fs =
"uniform sampler2D oe_layer_tex; \n"
"varying vec4 oe_layer_texc; \n"
"void my_color_filter(inout vec4 color) \n"
"{ \n"
" vec4 res = texture2D(oe_layer_tex, oe_layer_texc.st); \n"
" if ( res.a >= 0.0 ) \n"
" { \n"
" color.r=res.g+0.2;\n"
" } \n"
"} \n";

    // getOrCreate ensures we don't overwrite an existing VP.
    VirtualProgram* vp = VirtualProgram::getOrCreate( geom->getOrCreateStateSet() );

    // install the vertex function
    vp->setFunction( "my_filter_vertex",   vs, ShaderComp::LOCATION_VERTEX_MODEL );

    // install the color filter entry point. This is just a regular shader function,
    // not a pipeline injection, so just use setShader.
    vp->setShader( "my_color_filter", new osg::Shader(osg::Shader::FRAGMENT, fs) );

geom->getOrCreateStateSet()->getOrCreateUniform("oe_layer_tex", osg::Uniform::SAMPLER_2D)->set(0 );