@atux said:
But now the problem is this: for example, the values 60.0, 60.1, 60.2 inside the number box always get the same note. Is there a way to make all the notes sound at their true frequencies? In this way you can obtain a true continuous glissando.
No. 1/ MIDI note numbers cannot represent microtones. 2/ else/sfont~ ignores fractional note numbers too (so even if you bypass notein/noteout and put fractional note numbers directly into the sound font player, you still won't get microtones).
Basically: MIDI is outdated and boring, and we're still stuck with its 80s limitations 
Rant incoming... Actually, the VST framework has an extra data field for detuning, but I'm aware of only one plugin that actually implements it (the old VST2(!) version of Plogue's sforzando). I used to use that for microtuned sampler instruments, but then I had to migrate to yabridge instead of direct WINE support, and... yabridge ignores the detune field too
so that's gone. So what's left? sfizz = nope (and sfizz also makes it impossible to use MPE because "hey we're just a plugin, we'll never have to respond to MIDI through hardware so we're going to ignore MIDI channel completely, so, no MPE ever! We're stuck in 2015!") There's a cute sampler plugin called Decent Sampler which does support MPE, but it doesn't handle pitch bend right, and they ignore bug reports, so... for now, don't even think about continuous pitch in sampler plugins, at least not in Linux.
hjh