Add G68/G51 rotate/scale workspace (LinuxCNC)

[classicrocker883]

Description

Supposed to be able to rotate the workspace/bed.

Preliminary code, needs work+testing so far works well.
One stipulation I can make is when using G68 for square beds rotation should be in 90 degs. like +/- 90|180|270
Delta beds would not have this issue.

Another thing is when testing, you must use both X and Y in the coordinates - something like G1 X100 Y90
That is for now...
so, TODO: make it so can use either X or Y in Gcode moving commands.

See #27898

Requirements

Benefits

Configurations

Related Issues

[DerAndere1]

If using the LinuxCNC-compatible G10 L2 P- R- syntax for coordinate rotation is not desired, can Marlin use the Haas/Fanuc/RepRapFirmware-compatible G68 command instead of repurposing G7?

[classicrocker883]

If using the LinuxCNC-compatible G10 L2 P- R- syntax for coordinate rotation is not desired, can Marlin use the Haas/Fanuc/RepRapFirmware-compatible G68 command instead of repurposing G7?

so G7 doesn't appear to be used in Marlin, neither for G68. I suppose we could rename to G68 then? only reason for G7 was because it was close to G10

it sounds like G10 from LinuxCNC is just like G68, so that might work better

[DerAndere1]

Cool. Thanks. Can you briefly verify

-that G68 without x and y parameters rotates around the current Position and

-that the direktion if the rotation follows the conventions? I found this example for how it should work:

G68 X0 Y0 R90	(Rotates coordinate system 90° CCW around origin)
G01 X10 Y0	(Now moves along positive Y axis in machine coordinates)
G69	(Restores original coordinate system)

source:
https://cnccode.com/2025/06/23/g68-g69-in-cnc-mastering-coordinate-system-rotation-with-real-world-applications/

[DerAndere1]

I have some untested suggestions for improvement in this commit:
DerAndere1@83c8817

You can ignore changes to G10

[classicrocker883]

yes improvements for sure. in my testing with the simulator there seems to be some promises: G28 homes normally at any angle. but I think maybe that rotations should stick to +/- 90|180|270 for cartesian square beds. for Delta i suppose doesn't matter, but for consistency maybe have that can also stick to 90 deg increments?

im not sure if it rotates around the current position, but it rotates around the center (BED_SIZE / 2). and that was the issue I ran into, it started to rotate around its relative position. so, say you enter G1 X100 it goes to a different position every time (when rotation set). that would me it needs to know an absolute position/ or maybe saved position?

and thanks I will look into your commit and try it out 👍

[DerAndere1]

Workspace rotation is mainly used to simplify Gcode programming of parts with rotational symmetry. That rotational symmetry can be arbitrary (e.g. turbines with 3, 4, 5, 6,...100 blades) no restriction of angels please, that would marke behaviour once again incompatible with other controllers. Choosing angels wisely is task of the gcode programmer/CAM software/slicer

[DerAndere1]

Maybe the inverse_rotate_gcode_coordinates function has to be implemented as part of the get_destination_from_command function in gcode.cpp, taking into account current_position so that variables current_position and destination and cartes remain in cartesian Machine space

[classicrocker883]

checked out your code, seems to have some issues/typo

I did work on it a bit more and so far I have something working in my testing.

will need some more work as to make it so degrees are only +/- 90|180|270
I added this for square/non-Delta types

can you test it out using MarlinSimulator? I want to say it looks promising now

[DerAndere1]

With your G68 followed by multiple G1 commands I still got erratic movement. That is probably because G1 without X or Y resulted in destination[i} = current_position[i], see function get_destination_from_command in gcode.cpp.

With quite a bit of efford I got G68 working as documented in the Haas manual at https://www.haascnc.com/service/codes-settings.type=gcode.machine=mill.value=G68.html.

• syntax: G68 X Y R. X and Y should specify the center of rotation (no movement) for the active coordinate system. If X or Y are not specified, it should set the rotation center to the current position at the time when G68 is commanded.
  R specifies the angle in degrees. It must be allowed to set arbitrary angles to be compatible with all the other CNC controls. Software endstops in Marlin ensure that motion never exceeds the set limits in case the Gcode was not checked in CAM software.

In addition I have the P parameter working like in LinuxCNC G10.

• syntax: G68 P X Y R, Here, P should never change the active coordinate system. It should just specify for which coordinate system the rotation is set. Changing the active coordinate system should be done with G54...G59.
• G68 P0 X Y R sets rotation for the active coordinate system. G68 P1 X Y R sets rotation for the first coordinate system (the coordinate system that can be selected with G54)

Have a look at the last few commits of my branch: https://github.com/DerAndere1/Marlin/tree/coordinate_rotation

[classicrocker883]

oh nice. yeah that was something I noticed too - G1 moving commands without X or Y results in weird behavior, I might have forgot to mention it but I did write it in the Description at the top

Another thing is when testing, you must use both X and Y in the coordinates - something like G1 X100 Y90
That is for now...
so, TODO: make it so can use either X or Y in Gcode moving commands.

that is something that can probably be fixed easy

[DerAndere1]

It is already fixed at https://github.com/DerAndere1/Marlin/tree/coordinate_rotation. I tried to integrate individual changes from my branch in your branch. So far, correct motion was only achieved when introducing the additional raw_destination variable.

[thinkyhead]

Seems like this could supplant #21792 especially with the additional fixes from DerAndere1/Marlin/tree/coordinate_rotation . I will doublecheck and close that PR.

[thinkyhead]

Also consider G69 (Reset rotation) and G50, G51 which pertain to scaling — particularly useful for linear plotters.

[DerAndere1]

G69 is already added to my branch. I removed the P parameter from G68 because it will lead to confusion later if someone wants to add the G68.2 3D rotation command, where P selects between different modes. When I am at my PC I will have a look at PR 21792 for additional goodies and prepare a clean pull request targeting classicrocker's branch

[DerAndere1]

PR with improvements, including G50, G51 scaling is open at classicrocker883#3

[thinkyhead]

Pro Tip: When the rotation angle is set, calculate and cache the sin and cos of the angle and then use those cached values instead of calling sin() and cos() all the time in the motion code.

I leave this one to you.

[classicrocker883]

made some fixes according to comments, not all but some.

one issue that remains is when using like G1 X100 with single move command results in odd behavior. i suppose it corrects itself when entered again, but it works normally with two coordinates - G1 X0 Y0

reworked gcode.cpp to make this work with single move coordinates

[thinkyhead]

My text editor is trippin' today, dropping two characters here and there….

[classicrocker883]

My text editor is trippin' today, dropping two characters here and there….

mischievous and deceitful, chicanerous and deplorable

[DerAndere1]

Requiring G51 C to use the current position as the scaling center is not my preferred solution for dealing with the situation when rotation AND scaling are active. Maybe we have to enforce that rotation center and scaling center are identical in that case. But, conventionally, if rotation is cancelled with G69 and then G51 without C is sent, Marlin should use the current position at the time of the G51 command as the default scaling center.