imb.glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5f);
imb.glNormal3f(0.0f, 0.0f, 1.0f);
imb.glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), -width * 0.5f);
imb.glNormal3f(0.0f, 0.0f, 1.0f);
imb.glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5f);
imb.glNormal3f(0.0f, 0.0f, 1.0f);
imb.glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), -width * 0.5f);
}