Dropping frames / Low framerate

[GitBruno]

When I run the example example_send in this repository the frame rate of art-net messages is much lower than the OF framerate. It is so slow I am wondering if I'm doing something wrong. Setting ofSetFrameRate(1); does not help and the example still drops frames. You can see it more clearly when you add these lines:

ofSetColor(255,0,0);
ofDrawRectangle(ofGetFrameNum() % (int)sendData.getWidth(), 0, 1, 1);