G30 Rework

[kisslorand]

Description

G30 is all over the place. In rare occasions does a Z-Probe at a specified position.
For example:

• G0 X100 Y100; G30
• G30 X100 Y100

These two will not make a Z-Probe in the same position.
It's a whole other story if there's home offset and/or position shift (G92) is applied.

From my understanding G30 Xxxxx Yyyyy should do a probe where the nozzle would be in case of a G0 Xxxxx Yxxxx command and G30 should do a probe exactly where the nozzle is prior this command, all this regardless of home offset and/or position shift in use.

Requirements

• Z-Probe capability at a given coordinate (ex.: BL-Touch)

Benefits

This PR makes G30 work as expected, doing Z-Probe at the same point on the bed where the nozzle is/would be.

Related Issues

None reported, the bug was found during an attempt of adjusting the corners of the bed using G30.

[thinkyhead]

This all seems correct to me, thanks for the patch! I'll do more testing on it as I get into testing a recently revamped Chiron that has need of a new firmware.

[thinkyhead]

I don't know whether we ever decided that the parameters to G30 should be independent of the position shift / home offsets. This change makes the parameters to G30 logical position, whereas before the parameters specified the native position. We should consult other firmwares to see what is the de facto standard.

[kisslorand]

My logic is simple:

• G0 X15 Y15
• G30
  should have the same outcome as
• G30 X15 Y15

[thinkyhead]

Ok, well G0 X15 Y15 moves to X15 Y15 relative to the workspace origin, so it is a "logical position" according to our parlance. So the G30 should also be moving to the logical position relative to the workspace origin. The workspace origin does currently include the home offset, but there is some controversy about keeping it that way.