add scripting design documentation

3 files changed, 165 insertions, 0 deletions

diff --git a/design.tex b/design.tex
index 7b232fe..a89303a 100644
--- a/design.tex
+++ b/design.tex
@@ -36,6 +36,90 @@ workflows.
 
 \subsection{Scripting}
 
+The scripting interface was designed around a `target' \gls{api} (described by
+\cref{req:script:interface,req:script:user-class,req:script:direct-instance,req:script:direct-run}).
+An example of this \gls{api} is shown below:\noparbreak
+
+\begin{blockcode}
+class MyScript : public BehaviorScript {
+	void update() {
+		// update code here
+	}
+	// init() also exists, but is empty by default
+};
+
+{ // in scene initialization
+	GameObject & obj = ...;
+	obj.add_component<MyScript>();
+}
+\end{blockcode}
+
+The above call to \codeinline{GameObject::add_component} cannot work correctly
+without significantly increasing the complexity of the component manager, so the
+following restrictions were taken into account when creating the script system
+architecture:\noparbreak
+
+\begin{itemize}
+	\item The first template parameter passed to \codeinline{GameObject::add_component}
+		\emph{must} be a base `script \emph{component}' class, so each derived user
+		script class is instantiated in the same generic script list.
+	\item C++ does not allow passing types (i.e.~\codeinline{MyScript} in this case) as
+		function parameters, so a function call like
+		\codeinline{add_component<BehaviorScript>(MyScript)} cannot be realized.
+\end{itemize}
+
+\subsubsection{Architecture}
+
+The restrictions detailed at the start of this section are mitigated as
+follows:\noparbreak
+
+\begin{itemize}
+	\item User scripts are split into two classes---
+		\begin{enumerate}
+			\item a script \emph{interface} class (\codeinline{Script})
+			\item a script \emph{component} class (\codeinline{BehaviorScript})
+		\end{enumerate}
+	\item \codeinline{GameObject::add_component} receives the script \emph{component}
+		as template parameter
+	\item \codeinline{GameObject::add_component} now always returns a reference to the
+		component instance
+	\item The script component class has a setter function that takes a template
+		parameter for classes derived from the base script \emph{interface} class
+\end{itemize}
+
+\Cref{fig:class-scripts} shows the resulting structure as a class diagram. It
+contains the following classes:\noparbreak
+\begin{description}
+	\item[Script] This is the script \emph{interface}, and is used by the game
+		programmer to create derived script classes. All methods in this class are
+		declared virtual and have an empty implementation.
+
+		This class' methods are protected by default, and a friend relation to
+		\codeinline{ScriptSystem} is used to ensure only \codeinline{ScriptSystem} is
+		able to call these methods.
+
+		Only classes derived from \codeinline{Script} can be used with
+		\codeinline{BehaviorScript::set_script}'s template parameter \codeinline{T}. This
+		function returns a reference to the \codeinline{BehaviorScript} instance it was
+		called on so it can be chained after the call to
+		\codeinline{GameObject::add_component}.
+	\item[BehaviorScript]
+		This is the script \emph{component}, and is given as the template parameter to
+		\codeinline{GameObject::add_component}.
+
+		This class also uses a friend relation to \codeinline{ScriptSystem} to restrict
+		access to its private reference member \codeinline{script}.
+	\item[ScriptSystem] This is the system class that runs the methods implemented in
+		the derivative instances of \codeinline{Script}.
+\end{description}
+
+\begin{figure}
+	\centering
+	\includepumldiag{img/class-scripts.puml}
+	\caption{User script class diagram}
+	\label{fig:class-scripts}
+\end{figure}
+
 \subsection{Audio}
 
 \subsubsection{Library}
diff --git a/img/class-scripts.puml b/img/class-scripts.puml
new file mode 100644
index 0000000..8fc36c9
--- /dev/null
+++ b/img/class-scripts.puml
@@ -0,0 +1,48 @@
+@startuml
+!include theme.ipuml
+skinparam Linetype ortho
+skinparam Nodesep 75
+skinparam Ranksep 30
+
+class ComponentManager <<irrelevant>>
+
+package api {
+	class Component <<irrelevant>>
+
+	class Script {
+		# init() <<virtual>>
+		# update() <<virtual>>
+		--
+		- Script()
+	}
+
+	class BehaviorScript {
+		# BehaviorScript()
+		+ ~BehaviorScript()
+		--
+		+ set_script<T>() : this &
+		--
+		# script : Script *
+	}
+
+	BehaviorScript -u-|> Component
+	Script .u.> BehaviorScript
+}
+
+class System <<irrelevant>>
+class ScriptSystem <<Singleton>> {
+	+ get_instance() : ScriptSystem & <<static>>
+	+ update()
+	--
+	- ScriptSystem()
+	- ~ScriptSystem()
+}
+
+System <|-- ScriptSystem
+ScriptSystem .[norank]> ComponentManager
+
+ScriptSystem .[norank]> api.Script : < friend
+ScriptSystem .[norank]> api.BehaviorScript : < friend
+ComponentManager .[norank]> api.BehaviorScript : < friend
+
+@enduml
diff --git a/reqs.toml b/reqs.toml
index ed0b451..a83208e 100644
--- a/reqs.toml
+++ b/reqs.toml
@@ -84,3 +84,36 @@ Windows.
 # TODO: library documentation as quality factor?
 # TODO: modularity over less libraries? (i.e. why don't we just SDL2 everything?)
 
+[script:interface]
+type = 'system'
+priority = 'must'
+description = '''
+There is a base \codeinline{Script} class that has empty default
+implementations for functions that may be implemented by the game programmer.
+'''
+
+[script:user-class]
+type = 'system'
+priority = 'must'
+description = '''
+The game programmer implements scripts by creating classes derived from the
+\codeinline{Script} class.
+'''
+
+[script:direct-instance]
+type = 'system'
+priority = 'must'
+description = '''
+Unless explicitly changed by the game programmer, derived script classes cannot
+be instantiated directly, and must be instantiated by the component manager.
+'''
+
+[script:direct-run]
+type = 'system'
+priority = 'must'
+description = '''
+Unless explicitly changed by the game programmer, methods on instances of
+\codeinline{Script} (and derivative) classes cannot be called directly, and
+must be called by the script system.
+'''
+