It is important to note the following aspects when starting to make your theme, depending on how much you've experimented on existing themes, and compare the practices of such actions compared to now.
Date of change: starting on SM-SSC
You may have noticed themes even in SM5 and later that include header and footer, while technically they exist on those theme's scopes, they are not created by the engine. It is usually created on ScreenWithMenuElements decorations in a conditional function called StandardDecorationFromFileOptional, which looks for a metric on the current screen (or ScreenWithMenuElements as a fallback), to determine if it should be created or not.
Here's an implementation of such thing in Soundwaves.
-- Loads up a slew of objects to load into the screen, like how 3.9 does.
-- I prefer to keep these optional, incase another screen wants to hide
-- these elements.
return Def.ActorFrame {
StandardDecorationFromFileOptional("Header","Header"),
StandardDecorationFromFileOptional("Footer","Footer"),
StandardDecorationFromFileOptional( "Help", "Help" )
}
And its application on a screen that, for example, does not want both header and footer.
[ScreenInit]
ShowHeader=false
ShowFooter=false
Date of change: starting on SM-SSC
Starting in SM-SSC, fonts that were only number implemented now reside alongside the standard font glyphs in the Fonts folder (and are indicated with the [numbers] tag on their filename).
Date of change: SM4 Beta 5
Lua is the scripting language for modern StepMania builds. If any kind of XML loading is needed, you will need to instruct the user to enable "Quirks Mode", an option on the Preferences.ini file that allows loading of XML files in a compatibility layer.
Date of change: OutFox Alpha 3
cmd() is a string-like command that allows application of commands without performing the entire syntax in plain Lua. However, it is not recommended to use this for commands, as it can bring bugs which will be mentioned below, but also introduces loading overhead as it has to convert the string back into actual Lua.
-- cmd example
OnCommand=cmd(Center;rainbow;zoom,0.5);
-- Lua example
OnCommand=function(self)
self:Center():rainbow():zoom(0.5)
end
self cannot be utilized to obtain itself as self is a non-existant object in its scope.-- This will fail because the engine doesn't know what self is in this scope.
OnCommand=cmd(zoomx,self:GetZoomedWidth()*.5);