Wiley-World.of.Warcraft.Programming.A.Guide.and.Reference.for.Creating.WoW.Addons

474 Part III ■ Advanced Addon Techniquesaddon like the original version of Goose that could show or hide frames basedon three different factors (whether or not you were in stealth, in combat, ormounted), it needed eight different states (two possibilities for combat timestwo for stealth times two for mount equals eight) and it had to be able tohandle all the possible combinations of which state to go to when any one ofthese factors changed.Two things make the existing system generally easier to manage. First,snippets are capable of examining the game state, attributes on relevantframes, and similar factors, directly when triggered to determine the state theyshould set up. Second, the snippets associated with a frame can store as manydistinct pieces of information as they need to keep track of, in private globals.Private Global EnvironmentsEach function has an environment, which is a table where it stores and seeksany global variable references made in its body. Because each new functionis created with the same environment as the function that created it, all thefunctions created in the stock UI or addon files normally share the sameenvironment unless they specify otherwise at some point.The functions created when the secure handler infrastructure compilessnippets use their own environments, which is part of how their access togame information that’s not supposed to be used for secure actions is strictlycontrolled (such as how low on health your target is, for example). Becausefunctions are also normally found by calling global variables, functions thatretrieve prohibited information simply aren’t available from inside a secureenvironment. But snippets running in that environment can also store theirown globals there, which persist from one call to another. Moreover, all thesnippets associated with a frame typically share an environment, allowingthem to share input into their frame’s state.As a simple example of how this can be used, you can fix one of the issueswith BlessedMenus, namely, that when you open one menu on a frame andthen another, the first one stays open behind the second one.Open BlessedMenus.lua and look for your definition of the openSpellListsnippet. Alter it to look like this (changed lines are highlighted):local openSpellList = [[local menu = IsAltKeyDown() and “blessings“or IsControlKeyDown() and “heals“or IsShiftKeyDown() and “hands“menu = menu and self:GetFrameRef(menu)if lastMenu and lastMenu:IsShown() and ilastMenu:GetParent() == self thenlastMenu:Hide()if lastMenu == menu then