The scripting interface in Moho (Anime Studio) is divided into three "modules":
LM is the lowest-level module, and includes very basic objects like vectors and colors.
LM.GUI is a user interface module that is built on top of Moho's cross-platform user interface library. Scripts can use the user interface widgets in this module to build dialog boxes, and to set up custom interfaces for toolbar buttons.
MOHO is the module that is a direct interface into Moho itself. The objects and functions in the MOHO module allow scripts to create and manipulate layers, vector artwork, bone systems, and more.
Getting started with scripting
Moho scripts are written in Lua. This describes the basics of Lua: Programming in Lua
If you're already familiar with block-structured languages then you shouldn't have any real problems with Lua.
A word about Global variables.
Rule 1 in the Moho context: if you MUST use a global, then prefix it with some unique to you identifier ... see Script Structure. E.g. Moho uses LM_; other examples are HS_ , syn_, SZ_, AE_ ... It's best to use local variables by default except where necessary -- such as all your script functions that Moho expects to find (e.g. function HS_Myscript:Name() ).
Most of the Moho data objects will be of Lua type "userdata". e.g. as shown below the code
local vec = LM.Vector2:new_local()
creates "vec" as an object of class LM_Vector2
Note that the current versions of Moho (12 and 13) use Lua 5.2 -- the current Lua version is 5.4 -- make sure you use the right : Lua language reference docs
Interfacing with Moho
You're already in the right place for understanding how to get Moho and your scripts talking to each other...
A good place to start is to take a quick look (don't try to learn them!!) at the "core" classes in Moho : AnimChannel, M_Bone, M_Curve, M_Mesh, M_Point, M_Shape, M_Skeleton, MohoDoc, MohoLayer, ScriptInterface and get a feel for what's in them and how they fit together.
This scripting documentation has a Script Structure page that sets out the fundamental elements for menu, tool and layer scripts. There's also template generator accessible from the "tools" button.
If you fancy trying something before starting on a "serious" script, you might like to set yourself a simple challenge - e.g. draw a circle - centre is mouse click, radius is where the "drag" ends. (You could use the LM_Shape tool as a crib sheet for that if you get stuck.) Then build on that to get the circle to glide across the screen ... etc
Most Moho data objects don't need to be explicitly created -- calling something that "returns" a class gives you the userdata object: (e.g.) an M_Point class is returned by M_Mesh:Point(n) so:
local x = 5 -- assign a value
local vec = LM.Vector2:new_local() -- LM_Vector2
local mesh = moho:Mesh() -- ScriptInterface:Mesh
local pt = mesh:Point(x) -- M_Mesh:Point
vec:Set(pt.fPos) -- M_Point
sets vec to be the position of point "5"
As above, when a script creates new objects in Moho, it will most often not create them directly, but call a function to do the job. For example, a script never creates a new layer object directly, but tells Moho to insert a new layer:
-- *** Ask Moho to create a new vector layer ***
local layer = moho:CreateNewLayer(MOHO.LT_VECTOR)
Typically the only time a script might need to directly create a new object is for very simple object types, such as points, vectors, and colors. For example, to create a new 2D vector object, a script might do the following:
-- *** Create a new local variable ***
local vec = LM.Vector2:new_local()
-- *** Create a new global variable ***
XX_globalVec = LM.Vector2:new()
Your script throws an error such as "attempt to call method 'XXXXX' (a nil value)"
This is often found where you have the correct method but not the correct class of object.
e.g. myLayer:Layer(0) requires myLayer to be of class GroupLayer and the error will be generated if myLayer has not been cast as such by using ScriptInterface:LayerAsGroup (or, of course, is not any type of layer object)
Generic classes used as the foundation for specific layer types are MohoLayer and AnimChannel