I found the answer on my own:
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.clear:
// GLSurfaceView.queueEvent
surface.queueEvent(new Runnable() {
@Override
public void run() {
GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT);
}
});
break;
// ...
}
}