public void unapply(GOut g) {
   BGL gl = g.gl;
   gl.glSampleCoverage(1.0f, false);
   gl.glDisable(GL.GL_SAMPLE_COVERAGE);
 }
 public void apply(GOut g) {
   BGL gl = g.gl;
   gl.glEnable(GL.GL_SAMPLE_COVERAGE);
   gl.glSampleCoverage(cov, inv);
 }