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--- howto:combination_lock [2017-03-20 06:40] – [Explanation] skyjake
+++ howto:combination_lock [2017-03-20 16:20] (current) – [Introduction] skyjake
@@ Line 1: / Line 1: @@
+====== How to create a combination lock using XG ======
+//Work In Progress: This tutorial is not yet complete. It is published in the hopes that it might be of use but errors and omissions should be expected --danij, 12 October 2007//
+===== Overview =====
+Chances are, you have felt somewhat limited by [[games:doom]]'s key-locked doors when creating maps. Being continually faced with the same gameplay challenges is pretty un-interesting huh? Have you ever wanted to add a combination lock to secure an area in your map? Perhaps there is a secret laboratory in that deep space research lab with dangerous experimental weaponry hidden inside? This tutorial teaches you how to do just that.
+===== Introduction =====
+For this tutorial we will be utilizing XG to implement a combination lock. Be aware, that we will be chaining together multiple XG [[xg:line_type|line types]] to create a re-usable lock mechanism that can be used to activate another mechanism (here, we will use a simple door but in your own maps you could [[xg:class:build_stairs|build stairs]], [[xg:class:end_level|end the level]] etc...).
+In the process, we will discuss the event-driven nature of XG and how it can be used in different ways to replicate complex mechanisms. As such, this technique may not be suitable for those new to XG.
+===== Concept =====
+As already mentioned, we are aiming to create a combination lock, which (when the right combination is entered) will open a door. Before we go any further, lets first embelish this somewhat basic concept and try to define exactly the behavior we are trying to create.
+==== Requirements ====
+  *  The player should be able to manipulate the switches of the combination lock by //using// them.
+  *  Each time a switch changes state, we must check whether the current configuration activates the door.
+==== Features ====
+It would also be nice if we didn't have to create a tailored set of [[:ded|definitions]] for each instance of the combination lock. Lets outline some features that would improve the re-usability of our combination lock.
+  *  Any number of switches should be supported by an individual combination lock.
+  *  Any number of combination locks should be able to co-exist within the same map.
+  *  We should not have to create a new set of definitions for each combination lock.
+  *  The combination should be specified in the map-editor and NOT in the definition.
+===== Determining events =====
+/writeme
+===== The switches =====
+/writeme
+==== Definitions ====
+<code>
+Line Type {
+    Id = 1000
+    Comment = "Combo Lock ON Switch"
+    Class = none
+    Flags = player_use
+    Flags2 = when_act | when_deact | any
+    Type = flip
+    Count = -1
+    Event Chain = 32767
+    Act sound = "swtchn"
+    Act tag = 1
+}
+</code>
+<code>
+Line Type {
+    Id = 1001
+    Comment = "Combo Lock OFF Switch"
+    Class = none
+    Flags = player_use | active
+    Flags2 = when_act | when_deact | any
+    Type = flip
+    Count = -1
+    Event Chain = 32767
+    Act sound = "swtchn"
+    Act tag = 2
+}
+</code>
+==== Explanation ====
+/writeme
+===== The combination validator =====
+The final definition we need is that of the combination validator. Recall that earlier, when defining the switches we made use of the //Event Chain// paramater (**=32767**) to execute another linetype on activation/deactivation? This is that linetype.
+==== Definition ====
+<code>
+Line Type {
+    Id = 32767
+    Comment = "Combination validator"
+    Act message = "Access Granted";
+    Flags2 = any | when_act | line_act | line_inact
+    Class = activate
+    Count = -1
+    Line act lref = act_tagged
+    Line act lrefd = 1
+    Line inact lref = act_tagged
+    Line inact lrefd = 2
+    Ip0 = "lpref_tagged_ceilings"
+    Ip1 = 7
+}
+</code>
+==== Explanation ====
+Notice that there are no [[xg:triggers|(de)activation trigger]]s specified at all (normally, a linetype requires at least one trigger, for example [[xg:triggers#player_cross|player_cross]]). As our switch linetypes are //calling// the combination validator by way of their //Event Chain// paramater, there is no need to specify trigger(s). Furthermore this, means that this is a //virtual// linetype and cannot be used on a linedef in your map directly (note, that even if you //do// use it directly on a linedef - it will have no effect).

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