Take a look line 170 from https://code.google.com/p/tightvncpanel/source/browse/trunk/src/main/java/com/glavsoft/viewer/swing/Surface.java
This ((Graphics2D) g).setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY); make g.drawImage(offscreenImage,0,0,null); runs very slow on Mac Retina.
Solve: set the value to “VALUE_RENDER_SPEED” instead of VALUE_RENDER_QUALITY