Jog Speed slider

################################################################################################
# Description:
#     This script creates a HAL pin to read/write the jog speed selected in the axis ui.
#     It allows to access the ui jog speed via HAL (e.g. keep the ui in sync with physical
#     jog speed controls and vice-versa).
#    
#     HAL pin:
#         Name: axisui.jog.speed
#         Type: float
#         Direction: I/O
#
#        Compatibility:         
#            Tested on LinucCNC 2.8.2 only
#
#        Usage:
#            Set this file as the user command file in the ini's display section. See docs for details.
#                [DISPLAY]
#                USER_COMMAND_FILE = axis_hal_jog_speed.py
#
#            If a user command file is already in use, just merge the code accordingly:
#                - HalJogspeed.init() must be called in user_hal_pins()
#                - HalJogspeed.update() must be called in user_live_update()
#                - class HalJogspeed must be in scope
#     Note:
#         The jog speed slider moves in steps and has a max and min value.
#            Writing a value to the hal pin will select the nearest possible slider step    and then update
#            the hal pin to the resulting slider value.
#         The hal pin will also 'self correct' it's value to stay in the configured jog speed bounds
#            of the Axis-ui.
################################################################################################

# axis user callbacks, see docs
def user_hal_pins():
    HalJogspeed.init()

def user_live_update():
    HalJogspeed.update()

# keep axis namespace tidy
class HalJogspeed:
    @staticmethod
    def init():
        # create and init hal pin with current ui jogspeed
        comp.newpin("jog.speed", hal.HAL_FLOAT, hal.HAL_IO)
        comp["jog.speed"] = vars.jog_speed.get()
        
        ### hook into slider change callback
        # make python function availabe to tk
        nf.makecommand(root_window, "jogspeed_slider_change", HalJogspeed.__slider_change)
        
        # redirect the change callback
        root_window.tk.eval("${pane_top}.jogspeed.s configure -command jogspeed_slider_change")
    
    @staticmethod
    def update():
        # bail if hal pin is in sync with jog speed var
        if comp["jog.speed"] == vars.jog_speed.get(): return
        
        # write hal pin value to the jog speed var
        vars.jog_speed.set(comp["jog.speed"])

        # update the slider
        root_window.tk.eval("${pane_top}.jogspeed.s set [setval $jog_speed $max_speed]")
            
        # debug
        print "[HalJogspeed] HAL -> UI", vars.jog_speed.get()
        
    @staticmethod
    def __slider_change(val):
        # call the original tk callback; this will update the jog_speed var
        root_window.tk.call("update_jog_slider_vel", val)
        
        # write resulting jog speed to the hal pin
        comp["jog.speed"] = vars.jog_speed.get()
        
        # debug
        print "[HalJogspeed] UI -> HAL", vars.jog_speed.get()