GUI Development Reference

This document attempts to be a best practices reference for general use screen development.
While it’s possible to program just about anything to work with linuxcnc, using common frame work, language and configuration requirements allows easier transition between screens and more developers to maintain them.
That said, nothing in this document is written in stone.

1. Language

Python is currently the preferred language of linuxcnc’s screen code.
Python has a low entry bar for new users to modify the screens to suit them.
Python has a rich array of documentation, tutorials and libraries to pull from. + It is already used and integrated into linuxcnc’s system requirements.
While C or C++ could be used, it severely limits who can maintain and develop them.
It would be better to extend python with C/C++ modules for whatever function that requires it.

2. Basic Configuration

Currently, most screens use a combination of INI file and preference file entries to configure their functions.
INi text files are usually used for the common machine controller settings, while text based preference files are used for more GUI related properties (such as sounds, size, colors).
There can be other files used for translations, stylizing and function customization. These are highly dependant on the underlying widget toolkit.

2.1. INI [DISPLAY]

The [DISPLAY] section of the INI is for specifying screen related settings.

2.1.1. Display

The most important of is specifying the name of the screen that the linuxcnc script will use to load.
The screen program usually recognizes switches such as to set full screen.
Title is for the window title and icon is used for iconizing the window.

[DISPLAY]
DISPLAY = axis
TITLE = XYZA Rotational Axis
ICON = silver_dragon.png

2.1.2. Cycle Time

If settable, this is how to set the cycle time of the display GUI.
This is often the update rate rather then sleep time between updates.
A value of 100 ms (0.1 s) is a common setting though a range of 50 - 200 ms is not unheard of.

[DISPLAY]
CYCLE_TIME = 100

2.1.3. File Paths

If these functions are available in the screen here is how to specify the path to use.
These should reference from the current INI file, or allow ~ for the home folder, or allow use of absolute paths.

MDI_HISTORY_FILE = mdi_history.txt
PREFERENCE_FILE_PATH = gui.pref
LOG_FILE = gui-log.txt

2.1.4. Jog Increments

Radio buttons or a combobox are generally used for increments selection.
The linear increments can be a mix of inches or millimeters.
Angular increments are specified in degrees.
The word continuous is used to specify continuous jogging and probably should be added even if left out of the INI line.

INCREMENTS = continuous, 10 mm, 1.0 mm, 0.10 mm, 0.01 mm, 1.0 inch, 0.1 inch, 0.01 inch
ANGULAR_INCREMENTS = continuous, .5, 1, 45, 90, 360

2.1.5. Machine Type Hint

The screen often needs to be adjusted based on machine type. Lathes have different controls and display DROs differently. Foam machine display the plot differently.
The old way to do this was adding switches LATHE = 1, FOAM = 1 etc

MACHINE_TYPE_HINT = LATHE

2.1.6. Overrides

Overrides allows the user to adjust feed rate or spindle speed on the fly. Usually a slider or dial is used.
These settings are in percent.

MAX_FEED_OVERRIDE       = 120
MIN_SPINDLE_0_OVERRIDE    = 50
MAX_SPINDLE_0_OVERRIDE    = 120

2.1.7. Jog Rate

Most screens have slider controls to adjust the linear and angular jog speed rate,
These settings should be specified in machine units per minute for linear and degrees per minute for angular
Default refers to the starting rate when the screen is first loaded.

DEFAULT_LINEAR_VELOCITY =
MIN_LINEAR_VELOCITY =
MAX_LINEAR_VELOCITY =

DEFAULT_ANGULAR_VELOCITY =
MIN_ANGULAR_VELOCITY =
MAX_ANGULAR_VELOCITY =

2.1.8. Spindle Manual Controls

Manual controls for spindle control could be, (or a combinations of) buttons, sliders or dials
You can set limits that are less then the what the machine controller can utilize by setting these entries.
If your screen is capable of running multiple spindles, then should accept entries higher then the shown 0

SPINDLE_INCREMENT = 100
DEFAULT_SPINDLE_0_SPEED = 500
MIN_SPINDLE_0_SPEED = 50
MAX_SPINDLE_0_SPEED = 1000

2.2. INI [MDI_COMMAND]

Some screens use buttons to run Macro NGC commands.
They can be specified like these compact examples.
NGC commands separated by colons are run to completion before the next.
The optional comma separates text for the button from the NGC code.

[MDI_COMMAND_LIST]
MDI_COMMAND_MACRO0 = G0 Z25;X0 Y0;Z0, Goto\nUser\nZero
MDI_COMMAND_MACRO1 = G53 G0 Z0;G53 G0 X0 Y0,Goto\nMachn\nZero

2.3. INI [FILTER]

This sction allows setting of what files are shown in the file chooser and what filter programs will preprocess it’s output before sending it to linuxcnc.
The extensions are follows this pattern:
PROGRAM_EXTENSION = .extension,.extension2[space]Description of extensions
The filter program definitions are such:
filter extension = program to run

[FILTER]
# Controls what programs are shown in the file manager
PROGRAM_EXTENSION = .ngc,.nc,.tap G-Code File (*.ngc,*.nc,*.tap)
PROGRAM_EXTENSION = .png,.gif,.jpg Greyscale Depth Image
PROGRAM_EXTENSION = .py Python Script

# specifies what special 'filter' programs runs based on program ending
png = image-to-gcode
gif = image-to-gcode
jpg = image-to-gcode
py = python3

2.4. INI [HAL]

Most screens will need some HAL pins. They need to be connected after the screen creates them.+

2.4.1. Postgui Halfile

These files should be run one after another in order, after all the GUI HAL pins have been made.

[HAL]
POSTGUI_HALFILE = keypad_postgui.hal
POSTGUI_HALFILE = vfd_postgui.hal

2.4.2. Postgui Halcmd

These files should be run one after another in order, after all the POSTGUI files have been run.

[HAL]
POSTGUI_HALCMD = show pin qt
POSTGUI_HALCMD = loadusr halmeter

3. Extended Configuration

3.1. Embedding GUI Elements

Allowing users to build small panels independently, that can be embedded into the main screen is a common and very useful customization. Some screens allow embedding of 3rd party foreign programs, others only the native widget toolkit based panels.
Usually these are embedded in tabs or side panel widgets.
This is how to describe the optional title, loading command and widget name location:

EMBED_TAB_NAME=Vismach demo
EMBED_TAB_COMMAND=qtvcp vismach_mill_xyz
EMBED_TAB_LOCATION=tabWidget_utilities

3.2. User Message Dialogs

User dialogs are used for popping up import information (usually errors), that the user deems important.
Some stay up till the problem is fixed, some require acknowledgement, others a yes/no choice.

[DISPLAY]
MESSAGE_BOLDTEXT = This is an information message
MESSAGE_TEXT = This is low priority
MESSAGE_DETAILS = press ok to clear
MESSAGE_TYPE = okdialog status
MESSAGE_PINNAME = bothtest
MESSAGE_ICON = INFO

[DISPLAY]
MULTIMESSAGE_ID = VFD

MULTIMESSAGE_VFD_NUMBER = 1
MULTIMESSAGE_VFD_TYPE = okdialog status
MULTIMESSAGE_VFD_TITLE = VFD Error: 1
MULTIMESSAGE_VFD_TEXT = This is the longer text FOR MESSAGE NUMBER 1
MULTIMESSAGE_VFD_DETAILS = DETAILS for VFD error 1
MULTIMESSAGE_VFD_ICON = WARNING

MULTIMESSAGE_VFD_NUMBER = 2
MULTIMESSAGE_VFD_TYPE = nonedialog status
MULTIMESSAGE_VFD_TITLE = VFD Error: 2
MULTIMESSAGE_VFD_TEXT = This is the longer text FOR MESSAGE NUMBER 2
MULTIMESSAGE_VFD_DETAILS = DETAILS for VFD error 2
MULTIMESSAGE_VFD_ICON = INFO

MULTIMESSAGE_VFD_NUMBER = 3
MULTIMESSAGE_VFD_TYPE = status
MULTIMESSAGE_VFD_TITLE = VFD Error: 3
MULTIMESSAGE_VFD_TEXT = This is the longer text FOR Error MESSAGE NUMBER 3.
MULTIMESSAGE_VFD_DETAILS = We should do something about this message.
MULTIMESSAGE_VFD_ICON = WARNING