glVertex2f(peak_pos - 0.1, 0.0f);
glVertex2f(peak_pos - 0.1, 1.0f);
glVertex2f(peak_pos + 0.1, 1.0f);
glVertex2f(peak_pos + 0.1, 0.0f);
glEnd();
glVertex2f(peak_pos - 0.1, 0.0f);
glVertex2f(peak_pos - 0.1, 1.0f);
glVertex2f(peak_pos + 0.1, 1.0f);
glVertex2f(peak_pos + 0.1, 0.0f);
glEnd();