@Quickman it doesnt work for PC Engine, the only way to change aspect ratio is press start + B but it's stlll streched, here is a comparaison of the aspect ratio of Temper (on top) and Mednafen :
If anyone knows how to make mednafen have the perfect aspect ratio of Temper, please let me know.
I don't know what your complains are...
Temper
IS stretching the game and in a horrible way. (the pixels are not crisp)
Mednafen on the other hand, is displaying the game at it's native resolution. (using Start+B of course)
What you are complaining is the fact that Mednafen, when scaling up the game,
applies linear filtering.
I guess you could try to modify the configuration file in home/.mednafen/mednafen-09x.cfg
and change that line :
pce_fast.stretch 0
to this :
pce_fast.stretch aspect_mult2
You could try to do that too instead :
From
pce_fast.xscale 1.000000
to
pce_fast.xscale 1.250000