Add Z Fade Height to M420 output if it is enabled

[FHeilmann]

When M420 is used, it echos the current state of the leveling.
With this change M420 will also echo the current value of the z fade height (if it is enabled).

This makes it easier to deduce what value the z fade height currently has.

[FHeilmann]

One might also consider printing MSG_OFF instead of 0.0 by replacing

SERIAL_ECHOLNPAIR("Fade Height ", planner.z_fade_height);

with

SERIAL_ECHOLNPAIR("Fade Height ", planner.z_fade_height > 0.0 ? planner.z_fade_height : MSG_OFF);
let me know and I'll make the change.

[thinkyhead]

I like this.

"OFF" is ok. It does make an extra piece of work for hosts though 😉 .

Watch out for that ternary. Its terms are not the same type, and the compiler will bark. You'll need two echos, possibly.

SERIAL_ECHOPGM("Fade Height ");
if (planner.z_fade_height > 0.0)
  SERIAL_ECHOLN(planner.z_fade_height);
else
  SERIAL_ECHOLNPGM(MSG_OFF);

[FHeilmann]

I made the change as you suggested, I didn't know that the compiler wouldn't like a ternary like that. Good to know ;) Thanks for the heads up.

[thinkyhead]

I didn't know that the compiler wouldn't like a ternary like that. Good to know ;)

Yeah, think of it like this: Everything in C returns a value with a certain type. For example, this valid line of C simply sends the value of my_value to nowhere:

my_value;

A ternary is like a mini function that returns a single value of some type. You're allowed to do this too, as long as the two functions return the same type:

my_cond ? function_one() : function_two();

If functions don't return the same type, you have to cast:

int answer = my_cond ? (int)function_one_return_bool() : function_two_return_int();

[fiveangle]

You've just cleared up something that had perplexed me before Scott - thanks :)