Gtk::GLAarea does not draw

 std::vector<glm::vec2>vtx{
            { 0, 1 },
            { -1, -1 },
            { 1, -1 }
};
const char*vertex_source=
            "#version 460"
            ""
            "invec2position;"
            ""
            "void main(){"
            "   gl_Position=vec4(position,0,1);"
            "}";
const char*fragment_source=
            "#version 460"
            ""
            "outvec4 outColor;"
            ""
            "void main(){"
            "   outColor=vec4(1,1,1,1);"
            "}";

class canvas:public Gtk::GLAarea{
public:
    canvas() {

    }
    void on_realize() override {
        Widget::on_realize();

        make_current();

        // create shader
        shader=glCreateProgram();
        // attach vertex and fragment shaders

        // create buffer
        glGenBuffers (1, & vbo);
        // glBindBuffer, glBufferData 

        glClearColor(0,0,0,1);
    }
    void on_unrealize() override {
        Widget::on_unrealize();

        // destroy buffer and shader
    }
    US>bool on_render(const Glib::RefPtr<Gdk::GLContext>&) override {
        glClear(GL_COLOR_BUFFER_BIT);
        glUseProgram (shader);
        glBindBuffer (vbo);
        glEnableVertexAttribArray(0);
        glVertexAttribPointer(0,2,GL_FLOAT,GL_FALSE,0,nullptr);
        glDrawArrays (GL_TRIANGLES, 0, 3);
        glDisableVertexAttribArray(0);

        glUseProgram(0);
        glFlush();
    }
private:
    GLuint shader;
    GLuint vbo;
};

int main(intargc, char*argv[]){
    auto app=Gtk::Application::create(argc,argv);
    Gtk::Window;
    window.set_default_size(1000,700);
    canvas cv;
    window.add(cv);
    window.show_all_children();

    return app ->run(window);
}