How to draw near objects in first person view? (like a gun)

Question

I have my rendering engine more or less figured out. But I need to add functionality to render a 3d object that's pinned next to the camera (like holding a gun in an fps).

I tried first doing it by doing a lot of angle calculations and placing the object (in this case a cube) in the world at the coordinates where the camera would be looking at. This did not work out as I expected it to.

Then I searched on the web and people recommend drawing the object before applying the camera matrix. I've been trying to do this but with no success. The object doesn't appear at all.

The exact code segment is as follows:

        camera_matrix = camera.Matrix;
        GL.ClearColor(Color.White);
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

        GL.MatrixMode(MatrixMode.Modelview);
        GL.PushMatrix();
        GL.LoadMatrix(ref camera_matrix);

        foreach (var obj in farobjects)
        {
            GL.PushMatrix();
            GL.Translate(obj.Location);
            obj.Render(camera);
            GL.PopMatrix();
        }
        GL.PopMatrix();

        GL.MatrixMode(MatrixMode.Modelview);
        foreach (var obj in nearobjects)
        {
            GL.PushMatrix();
            GL.LoadIdentity();
            GL.Translate(obj.Location);
            obj.Render(camera);
            GL.PopMatrix();
        }

Any ideas on what I'm doing wrong? The object I placed does not appear at all. I tried moving it to (1,0,1), (0,0,1) and (1,0,0) and the object is nowhere to be found.

Answer 1

I finally found the solution. I had to create a second camera matrix for this and apply it, as well as flush the z buffer.

        camera_matrix = camera.Matrix;
        GL.ClearColor(Color.White);
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
        GL.MatrixMode(MatrixMode.Modelview);

        GL.PushMatrix();
        GL.LoadMatrix(ref camera_matrix);
        foreach (var obj in farobjects)
        {
            GL.PushMatrix();
            GL.Translate(obj.Location);
            obj.Render(camera);
            GL.PopMatrix();
        }
        GL.PopMatrix();

        GL.Clear(ClearBufferMask.DepthBufferBit);

        GL.PushMatrix();
        Matrix4 modelview = Matrix4.LookAt(Vector3.Zero, Vector3.UnitZ, Vector3.UnitY);
        GL.LoadMatrix(ref modelview);

        foreach (var obj in nearobjects)
        {
            GL.PushMatrix();
            GL.Translate(obj.Location);
            obj.Render(camera);
            GL.PopMatrix();
        }
        GL.PopMatrix();