Have you tested this? FIX2INT() only works with fixnums.

Yes,
the only games that I encountered this problem are some rgss1 games,
that use a plugin to determine the characters position.
float value (X,Y position of the character) & rational value (expected X,Y new value)
The new value is determined from the move direction of the character.

Yeah, RGSS3 also supports rational numbers but your change may only appear to work. Could you please try something like Rect.new(Rational(10, 10), 0, 0, 0) and check the value of its x attribute? I can't compile mkxp at the moment and there's no test suite or build bot.

IMHO the type check isn't necessary anyway. *out = NUM2INT(arg); is good enough (and rb_rescue() if the custom error message should be kept). This would add support for complex numbers too: Rect.new(Complex(10, 0), 0, 0, 0).

Can you give another test?
My Falcon-mkxp has unlocked resolution, so the x result will always deffer, depending on the game resolution & monitor resolution & position of the window.

• I had tested it against these examples
  https://ruby-doc.org/core-2.5.3/Rational.html
  and the only ones that could not resolve (if I remember correctly) were the examples with half keyword arguments e.g.
  Rational(25, 100).round(1, half: :up) #=> (3/10)

X should always be 1. But it can be tested with any other integer attribute:

s = Sprite.new
s.z = Rational(10, 2)
p s.z # => 5

Thank you.
I created 2 events to call the test scripts and both of them
return positive random(?) values with 8 digits(!) instead of returning x=1 & s=5.