How to draw polygon with 3D points in modern openGL?

Question

I know in 2.0- openGL we can draw a line simply like this.

glBegin(GL_LINES);  
glVertex3f(20.0f,150.0f,0.0f);  
glVertex3f(220.0f,150.0f,0.0f);  
glVertex3f(200.0f,160.0f,0.0f);  
glVertex3f(200.0f,160.0f,0.0f);  
glEnd();

but how to do similar thing in modern openGL(3.0+)

I have read Drawing round points using modern OpenGL but the answer is not about certain point,since I want to draw polygon with points have certain coordinates,it's not quite helpful.

I use this code,but it shows nothing except a blue background.what do I missed?

GLuint VertexArrayID;
    glGenVertexArrays(1, &VertexArrayID);
    glBindVertexArray(VertexArrayID);

static const GLfloat g_vertex_buffer_data[] = {
        20.0f, 150.0f, 0.0f, 1.0f,
            220.0f, 150.0f, 0.0f, 1.0f,
            200.0f, 160.0f, 0.0f, 1.0f
    };

GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW);

do{

    // Clear the screen
    glClear( GL_COLOR_BUFFER_BIT );

    // 1rst attribute buffer : vertices
    glEnableVertexAttribArray(0);
    glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
    glVertexAttribPointer(
        0,                  // attribute 0. No particular reason for 0, but must match the layout in the shader.
        4,                  // size
        GL_FLOAT,           // type
        GL_FALSE,           // normalized?
        0,                  // stride
        (void*)0            // array buffer offset
    );

    // Draw the triangle !
    glDrawArrays(GL_LINES, 0, 2); // 3 indices starting at 0 -> 1 triangle

    glDisableVertexAttribArray(0);

    // Swap buffers
    glfwSwapBuffers(window);


} // Check if the ESC key was pressed or the window was closed
while( glfwGetKey(window, GLFW_KEY_ESCAPE ) != GLFW_PRESS &&
       glfwWindowShouldClose(window) == 0 );

Answer 1

1) You have to define an array of vertices, that contain the points of your polygon lines. Like in your example:

GLfloat vertices[] =
{
    20.0f, 150.0f, 0.0f, 1.0f,
    220.0f, 150.0f, 0.0f, 1.0f,
    200.0f, 160.0f, 0.0f, 1.0f
};

2) You have to define and bind a Vertex Buffer Object (VBO) to be able to pass your vertices to the vertex shader. Like this:

// This is the identifier for your vertex buffer
GLuint vbo;
// This creates our identifier and puts it in vbo
glGenBuffers(1, &vbo);
// This binds our vbo
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// This hands the vertices into the vbo and to the rendering pipeline    
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

3) Now we are ready to draw. Doing this:

// "Enable a port" to the shader pipeline
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
// pass information about how vertex array is composed
glVertexAttribPointer(0, // same as in glEnableVertexAttribArray(0)
                      4, // # of coordinates that build a vertex
                      GL_FLOAT, // data type
                      GL_FALSE, // normalized?
                      0,        // stride
                      (void*)0);// vbo offset

glDrawArrays(GL_LINES, 0, 2);
glDisableVertexAttribArray(0);

Step 1) and 2) can be done before rendering as initialization. Step 3) is done in your rendering loop. Also you'll need a vertex shader and a fragment shader to visualize the line with color.

If you don't know anything about these things and like to start with OpenGL 3, I'd suggest to start over with a tutorial like this: http://www.opengl-tutorial.org/beginners-tutorials/tutorial-1-opening-a-window/