NWC Object Plugin API

Object Type Naming Conventions

NoteWorthy Composer includes support for a new generic object type, that internally is of type User. This object includes a sub-type which can be subclassed using Lua plugin scripts. An example custom NWC object represented by nwctxt is shown here:


Each <Object-Type-Name> object can be subclassed with a Lua script that has a specific naming convention:


The <Object-Type-Name> must start with a letter, and is currently restricted to the ASCII character set. It is recommended that all object types include a short author identifier with a dot prefix. For example, all object types created by Noteworthy Software will always include a .nw extension to uniquely identify them.

Object Class

Every object instance is marked with special Class designation, which can be one of:

Event Methods - Hooking into NWC

Each object type's Lua script must return an event method table that will be used to subclass any objects that share the matching <Object-Type-Name>. This should be done at the end of the plugin's script:

return {
    nwcut     = {['User tool action 1']='Clip',['User tool action 2']='File'},
    spec      = {{id='field1',type='text',default=''},{id='field2',type='text',default=''}},
    menu      = {{type='command',name='cmd1...',separator=false,checkmark=false,disable=false,data=1},
    menuInit  = function(t) end,
    menuClick = function(t,menu,choice) end,
    create    = function(t) end,
    audit     = function(t) end,
    spin      = function(t,dir) end,
    onChar    = function(t,c) end,
    transpose = function(t,semitones,notepos,updpatch) end,
    play      = function(t) end,
    span      = function(t) return 1 end,
    width     = function(t) return 0 end,
    draw      = function(t) end

This method table is used as an event dispatch mechanism which forwards the listed events into the object's plugin module. The supported event methods are:

Method Parameters Event
create t A new object is being added to the staff. Parameter t provides read/write access to the properties for this object.
audit t This is called when an object is loaded (via file/clipboard) or a View->Refresh Score is performed. Parameter t provides read/write access to the properties for this object.
spin t
The user applies a '+'/'-' increment/decrement operation against the object while in the editor. Parameter t provides read/write access to the properties for this object. Parameter dir is 1 or -1 to indicate the direction of the spin action.
onChar t
The user has pressed a character on the computer keyboard while targeting this object (it is selected by itself from within the editor). Parameter t provides read/write access to the properties for this object. Parameter c is the numeric character key that has been pressed. Returns true if the plugin has responded to the key withs an action. Returns false if the key should be handled in the standard fashion by the editor.
transpose t
The staff is being transposed by the user. Parameter t provides read/write access to the properties for this object. Parameter semitones can be anything from -12 up to 12. The notepos indicates the preferred amount of shift that should be applied to a note position on the staff, and should be between -7 and 7. The updpatch indicates if the play back instrument will be transposed accordingly.
play t The staff notation is being compiled into a performance using a buffered sequence of MIDI events. Parameter t provides read access to the properties for this object.
span t An optional method called for objects using the Span class. This returns a value pair: the size of the span, and one of the nwctxt.SpanTypes (notes,syllables,bars,ticks,items) with notes being the default. Parameter t provides read access to the properties for this object.
width t The object is being evaluated for inclusion in a displayable medium, such as an editor view or printed page, and it is given an opportunity to request a reserved width on the staff. The method should retuurn a required width, or no width will be reserved for the object. Parameter t provides read access to the properties for this object.
draw t The object needs to be rendered into a window or onto a printed page. Parameter t provides read access to the properties for this object.
menuInit t The object has been right clicked in the editor, and a menu is about to be presented. Parameter t provides read access to the properties for this object, which can be used to alter the contents of the its menu table.
menuClick t
A choice has been selected from the object's right click menu. Parameter t provides read/write access to the properties for this object. The menuidx is the key into the menu table, and choice is the list choice index, or nil for menu commands.

The nwcut Table - Defining User Tool Actions

A plugin has the optional ability to define one or more actions that can be accessed from the User Tool command. This is done via the nwcut return entry, defined as an associative table with the key being the action to perform, and the value indicating whether the command accepts File or Clip content:

nwcut = {
    ['clip action']='Clip',
    ['file action']='File'

The plugin then implements the user tool actions in a nwcut environment hook. The presence of the nwcut package indicates that the script's entry point is actually from a user tool invocation. This environment is fully described in the User Tool API section.

A full sample plugin that delivers a series of user tools without any traditional object support is shown below:

-- This object plugin is used to provide a series of user tools. It is not meant to provide any
-- direct user object support via Insert, Object.

if nwcut then
    -- This is the user tool entry point. All user tool code must be done from within this nwcut
    -- environment hook. The standard object plugin environment is not available when run from this
    -- entry point. The object name and action are passed into this entry point via the arg[] table.
    local userObjTypeName = arg[1]
    local userAction = arg[2]

    nwcut.warn(string.format('Object: %s, Action: %s',userObjTypeName,userAction))

-- Everything below here runs in the nwc object plugin context. In this example, we simply
-- provide a set of user tools, and disable the corresponding object's create action.

return {
    create = false, -- excludes object from Insert, Object list
    nwcut = {
        ['Action 1'] = 'Clip',
        ['Action 2'] = 'File'

The spec Table - Defining Object Properties

Although not required, it is recommended that an object's event method table return an additional spec entry. This is used to:

The spec table should list all of the possible fields that are supported by the object type, and describe the nature of the value that each field will contain. The following example demonstrates all of the available types that are supported by the spec table:

local obj_spec = {
    {id='field1',label='Enable field&1',type='bool',default=true},
    {id='field4',label='Apply duration',labelFirst=true,type='bool',default=true,separator='-'},
    {id='field5',label='Field5',type='int',default=0,min=0,max=100,width=5,separator=' '},
    {id='field6',label='Field6',type='enum',list=nwc.txt.NoteDuration,default=nwc.txt.NoteDuration[3],separator=' '},
    {id='field8',label='Select from list',type='enum',default='Quarter',list={'Whole', 'Half', 'Quarter', 'Eighth', 'Sixteenth', 'Thirtysecond', 'Sixtyfourth'}},

Some additional notes about the field types:

The obj_spec should be included in the table returned by the plugin:

return {
    spec = obj_spec,
    create = do_create,

When this is done, all property values for an object will be filtered through the lens of its spec table. If a property does not exist in the object, then the default value from the spec will be returned. For properties of type bool, any of the following case insensitive values will result in a true return value: y, yes, true, 1. Any other value will yield false. Numeric values (int or float) that are out of range will return the min or max, depending on which extreme was exceeded. For enum fields, the default will be returned if the current property value is not found in the enumerated list. The list is generally case sensitive, but you should not use duplicate values of differing case.

The menu Table - Custom Command Actions

An object's event method table can return an additional menu entry. This is used to construct a context menu when an object's anchor is right clicked in the editor. It is also accessible when the object is selected by itself in the editor. Each active menu entry triggers an menuClick event when an item is selected by the user.

The following example demonstrates the menu table:

local menu1List = {'subCommand 1','subCommand 2','subCommand 3','subCommand 4','subCommand 5'}

local obj_menu = {
    {type='choice',name='Menu Command 1',separator=false,disable=false,default=nil,list=menu1List,data=nil}
    {type='command',name='Menu Command 2...',separator=true,disable=false,checkmark=true,data={custom1='anything'}},

local function obj_menuInit(t)
    -- this can change obj_menu as needed
    obj_menu[2].checkmark = t.opt1

local function obj_menuClick(t,menuidx,choice)
    if menuidx == 1 then
        print('Menu1 Clicked',obj_menu[1].name,obj_menu[1].list[choice])
    elseif menuidx == 2 then
        print('Menu2 Clicked',obj_menu[2].name)

The menu and its supporting events must be included in the table returned by the plugin:

return {
    menu      = obj_menu,
    menuInit  = obj_menuInit,
    menuClick = obj_menuClick,

The menuClick event handler is free to change any values in the object via the t argument. The program takes care of managing the editor's undo mechanism. If a prompt/dialog is canceled by the user while in the menuClick function, any changes made to the object are ignored. A custom 'data' field can be included in any menu table entry, and can be assigned any values that might be needed in the menuInit or menuClick functions.

Support Packages

The following support packages are available for use by the object plugin, depending on which event method is currently executing in context:

The following reference objects are also available for use:

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