Updating QGLWidget - event or signal/slot?

I need to flash some images with very precise timing (order of milliseconds) for which I developed a subclass of QGLwidget. The images are loaded as textures at initialization. I am using a QTimer instance to change the image being displayed. The timer's timeOut signal is connected to a timeOutSlot which does some file I/O and then calls updateGL().

While I understand that event handlers are for external events and signal/slot is for communication internal to the GUI, I could also implement this as a t开发者_开发百科imeOutEvent handler.

Is there any performance difference between the two? Any performance penalty above 2-3 milliseconds is important to me (hardware is average, say Intel core 2 duo T5700 with nVidia 8600M GT graphics card).

Signals and slots are about 10 x slower than the plain old function calls. But they are definitely not so slow that they would take milliseconds to process. The time to process one signal is about 0.001 ms (see slide 27).

You say that you are requiring a very precise timing, so are you aware how the display refresh rate affects the drawing? Image is (usually) drawn using 60 Hz refresh rate. The time between images is 16.7 ms so that is the maximum accuracy you can get.

I would say signal/slot because events are added to an event queue where Qt often does call optimisations and importance ordering, whilst s/s are executed immediately - albeit slower than direct calls.