first we declare an ui_element like a knob, button, slider etc inside the on init callback like so:

on init       
    declare ui_button $my_button
    declare ui_slider $my_slider(0,10000000)
    declare ui_table %my_table[8](400, 100, 16)
end on

on ui_control($my_button)

on ui_control($my_slider)

on ui_control(%my_table)
then we simply put it’s variable name inside the brackets to associate the ui_element with the on ui_control callback.
When moving or changing the ui_element, the associated ui_control and all code in it is executed.

declare ui_switch $hit_me

first we declare a simple button or switch

make_perfview

keeps the UI visible outside the edit mode

on ui_control($hit_me) ... end on

we associate the button to the ui_control by just putting the buttons variable name between the brackets.
now being associated, the callback and the message command in it will be executed whenever the button is pressed:

message("ouch, you hit me")

in this case it is just a simple message displayed in the lower status bar of Kontakt

declare ui_slider $my_knob(0,1000000) declares a slider. 0 is the min value, when the slider is on left position. 1000000 is the max value when the slider is on the right position.

declare ui_label $value(1, 1) declares a label which will display the knob’s current value

make_perfview makes the ui visible outside the edit mode

on ui_control($my_knob) defines the ui control which is “linked” with $my_knob. To link the ui control to any other element simply change $my_knob to your ui variable. We can add as many on ui_controls as we want. Well almost as many. There is a limit due to Kontakt resources but its hard to reach that limit so we don’t care right now.

set_control_par_str(get_ui_id($value),$CONTROL_PAR_TEXT,$my_knob) this displays the currents knob’s value as label text. This line gets executed again and again whenever the knob is turned. So the label text gets always updated.

declare ui_knob $volume(0, 1000000,500) 

first we declare a simple knob with the range 0 to 1.000.000.
0 is the min value and 1.000.000 is the max value.

Note: almost all the Kontakt engine parameters like volume, pan, fx, EG, LFOs work with values from 0 to 1.000.000 So in this case a value of 0 for the volume represents  -inf dB and 1.000.000 is +12.dB. Also read more about this in the set_engine_par() article

set_knob_unit($volume,$KNOB_UNIT_DB)

then we set the knob’s unit to dB.

declare @disp

we declare a helper variable for storing the real volume coming from the Kontakt engine.

on ui_control($volume) ... end on

once again, when turning the $volume knob, this callback and all the code in it gets executed:

set_engine_par($ENGINE_PAR_VOLUME,$volume,-1,-1,-1)

first we use the set_engine_par to send the knob’s current value, to the Kontakt engine.
The knob’s current value is hold inside $volume and it gets automatically updated when we turn the knob.

the Kontakt engine then interprets all the values that that we submit and knows which engine parameter we want to address and of course it also gets updated with the new volume value that we submit via $volume

@disp := get_engine_par_disp($ENGINE_PAR_VOLUME,-1,-1,-1)

actually we want to show the real volume data when turning the knob. But remember our knob’s still holds some inconclusive values from 0 to 1.000.000
So if we set the main volume to 3 dB our knob would show something like 707143 instead of +3dB
No one would be able to tell the actual Volume then. Even worse, remember the knob already shows the unit dB. So it says 707143 dB. Imagine 707143 dB hitting your ears

Long story short via get_engine_par_disp() we fetch the the real volume data directly from the Kontakt engine and store it into the @disp variable.

set_knob_label($volume, @disp)

lastly we simply pass the correct volume data to our knob’s label

Of course we can also directly pass the correct volume data without using @disp at all, like so:

set_knob_label($volume, get_engine_par_disp($ENGINE_PAR_VOLUME,-1,-1,-1))