How to use subwindows in opengl

Question

I am trying to use subwindows to generate an object out of a curve by rotating it. I am able to generate all the curves. Now I have also divided the window in two parts. I want to draw curves in the left subwindow and want to generate a solid by rotating it along an axis in the right. I am not able to draw anything in the right subwindow.

Edit:

Ok this is how I am drawing dots in the left part. The dots are basically clicks by user. I capture those events and make a list and then using a for loop print them.

// This function takes a list of points and draws the dots in the screen
void drawDot(vector<vec2> listPts)
{
    glBegin(GL_POINTS);
    glColor3f(1.0,1.0,1.0);

    if(j==0) // J=0 means points are being added using add option, no insert after is currently being used
    {
        for(int i=0;i<listPts.size();i++)
        {
            glVertex2i(listPts[i].x,listPts[i].y);
        }
    }
    else if(j!=0)// this else part is for making selected points look red, as for this j!=0 
    {
        for(int i=0;i<listPts.size();i++)
        {
            if(i==j ) // make only the selected point red
            {
                glColor3f(1.0,0.0,0.0);
                glVertex2i(listPts[i].x,listPts[i].y);
            }
            else // rest all the points are same as before i.e. white
            {
                glColor3f(1.0,1.0,1.0);
                glVertex2i(listPts[i].x,listPts[i].y);
            }
        }
    }

    glEnd();
    glFlush();
}

Now suppose I have a set of points. I just want to draw in the right subwindow the same points just to see if it is working. So, I have created a button and when ever I press the button, I want to switch to the right window and draw something. I used debug in VS2010 and checked that if the drawing func is at all called and it is being called and still nothing comes in the screen.

this is the function I am using to draw in the second window.

void drawDotWin2(vector<vec2> listPts)
{
    glBegin(GL_POINTS);
    glColor3f(1.0,1.0,1.0);

    for(int i=0;i<listPts.size();i++)
        {
            glVertex2i(listPts[i].x,listPts[i].y);
        }
    glEnd();
    glutWireTeapot (0.5);
    glFlush();
}

when I press the button. the above function is called but nothing happens. Is my co-ordinate system wrong? I didn't do much to set the coordinate system though.

Answer 1

I suggest to avoid GLUT utilities as much as possible, especially when they are not strictly necessary in the application implementation; glutCreateSubWindow could be one of them.

If you need to split you window in different sections, learn how to use glViewport.

For example, if the main window has a client area of 800x600 pixels, and I want to split horizontally the window, the draw routine would be:

void draw()
{
    // Draw on left side
    glViewport(0, 0, 400, 600);
    glClear(...);
    gluOrtho2D(0, 0, 400, 600);

    // ... DrawCommands1

    // Draw on left side
    glViewport(400, 0, 400, 600);
    glClear(...);
    gluOrtho2D(0, 0, 400, 600);

    // ... DrawCommands2
}

In a such way, the two drawings does not overlap. The primitives drawn on each side are clipped by the defined viewport area, defined in pixel coordinates relative to the main window client area.

The projection matrix (in the above case a 2D orthogonal) is relative to the viewport are, not to the window area, indeed you don't need to worry about viewport position.

Note also that each GLUT sub-windows creates an OpenGL context, indeed each GLUT sub-window holds its own state, and a state change don't affect the other ones. Instead, in my answer the two routines shares the very same OpenGL context.