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diff --git a/docs/XmlConfiguration.tex b/docs/XmlConfiguration.tex new file mode 100644 index 0000000..6f45de2 --- /dev/null +++ b/docs/XmlConfiguration.tex @@ -0,0 +1,223 @@ +\documentclass{article} +\usepackage{fullpage} +\begin{document} + \title{XML in SmootLight: Configuration++} + \author{Russell Cohen} + \date{\today} + \maketitle + \section{Motivation} + Why use XML (or any non-code language for that matter) to configure code? 2 Reasons: + \begin{itemize} + \item We would like small changes (like changing the color, speed, or type of behavior) + to be as quick as possible, and require modifying only 1 piece of code. + \item We would like these changes to be able to be made \emph{programmatically} + \item (Not applicable to python, but important in languages like Java or C): We want to + be able to make changes \textbf{without} having to recompile the source. + \end{itemize} + As you will see, however, XML in SmootLight goes beyond simple configuration. XML in + SmootLight allows us to declare a LightSystem (an inherently non-declarative thing) in the + same way you might write a webpage in HTML. We will refer to the XML system here-on-in as + `SmootConf'. \textbf{The fastest way to get familiar with SmootConf is simply to look at + the XML files in the configuration file. However, if you want a more structured approach to + its feature and subtleties this document should do the job.} Without any further ado, lets start looking at + how this all works. + \section{Declaring a class in SmootConf} + The most common thing done is SmootConf is declaring a class -- Class declaration code will + get parsed by SmootLight at runtime and \emph{actually} \textbf{declare} your classes for + you, exactly how you describe them. Classes are declared under a broader + \texttt{Configuration} tag which we will describe later. Lets look at the declaration of + \texttt{PygameInput}, an input that takes data from a Pygame window. + \begin{verbatim} + <InputElement> + <Class>inputs.PygameInput</Class> + <Args> + <Id>pygameclick</Id> + <RefreshInterval>10</RefreshInterval> + <Clicks>True</Clicks> + </Args> + </InputElement> + \end{verbatim} + The first attribute we see is the \texttt{Class} attribute. This specifies what + fully-qualified Python class to this object should be an instance of. In this case, it is + an instance of PygameInput, which lives in the inputs module/folder. Next, we see the + \texttt{Args}. The Args are where \emph{every} piece of configuration (except the actual + Class) goes. Let me repeat that, becuase it is a common sticking point. If you place + something in the configuration outside of the \texttt{Args} tag, it will not be read. + Period. + + If you are familiar with the SmootLight system, you will know that many objects in + SmootLight behave like dictionaries -- you can use statements like + \texttt{Self['ParamName']} to access parameters. If you have ever wondered where this + mystery dictionary is filled from, look no further -- it is here in the Args tag. + + Lets dig into the contents of the Arg tag. First we see \texttt{Id}. All components in the + SmootLight system are \emph{not} explicitly required to have an Id + specified.\footnote{Components declared without Id's will get a randomly assigned Id at + declaration time} + However, if you want to be able to reference this class in other places in the XML (which + we will look into later), you will need to specify and Id. The other two parameters are + simply bits of configuration which will get passed to PygameInput when it gets instantiated. + + \section{The Structure of a SmootLight Configuration Document} + The individual class declarations are the `leaves' of a full configuration document that + gets interpreted by the parser. In order for the parser to know what to do with them, it + also needs the branches. The structure of these `branches' (tags) follow: + \begin{verbatim} + <LightInstallation> + <InstallationConfiguration> + <Defaults /> + </InstallationConfiguration> + <PixelConfiguration /> + <PixelMapperConfiguration /> + <RendererConfiguration /> + <InputConfiguration /> + <BehaviorConfiguration /> + </LightInstallation> + \end{verbatim} + Under each of the tags indicated, place the classes that you want to instantiate in that + category. Each category has a different child tag: + \begin{itemize} + \item PixelConfiguration: PixelStrip + \item PixelMapperConfiguration: PixelMapper + \item RendererConfiguration: Renderer + \item InputConfiguration: InputElement + \item BehaviorConfiguration: Behavior + \end{itemize} + Some further clarification on this: Recall in the previous section we inspected the + declaration of the Input element. The input configuration for that system might have looked + like: + \begin{verbatim} + <InputConfiguration> + <InputElement> + <Class>inputs.PygameInput</Class> + <Args> + <Id>pygameclick</Id> + <RefreshInterval>10</RefreshInterval> + <Clicks>True</Clicks> + </Args> + </InputElement> + </InputConfiguration> + \end{verbatim} + \texttt{InputElement}s live under the broader \texttt{InputConfiguration} tag. Thats all in + terms of basic configuration -- all other features are going to be specific to the + particular class you are declaring (and the class should specify those). However, the + system also offers a lot of features to give you more power and flexibility, as well as + minimizing repeated XML. + \section{XML Inheritance} + SmootConf allows you have XML objects inherit from this other. Think of this as an + X:Include crossed with OO style inheritance, if those are familiar concepts. The most basic + tag of inheritance in SmootConf is the \texttt{InheritsFrom} tag. Here is a quick example + of it in action: + \begin{verbatim} + <Renderer Scale="4"> + <InheritsFrom>renderers/Pygame.xml</InheritsFrom> + </Renderer> + \end{verbatim} + + And the contents of \texttt{renderers/Pygame.xml}: + \begin{verbatim} + <Renderer> + <Class>renderers.PygameRenderer</Class> + <Args> + <Id>pygamerender</Id> + <displaySize>(1300,50)</displaySize> + </Args> + </Renderer> + \end{verbatim} + + The \texttt{InheritsFrom} tag indicates to look in the XML File indicated, parse it, and + recursively merge its tags with the siblings of the \texttt{InheritsFrom} tag. From a high + level, the algorithm works as follows: + + \begin{itemize} + \item For every tag: + \item If the tag is in the inheriter, use that. Otherwise, use the inherited tag. + \item Recurse to children. + \end{itemize} + + SmootConf adds a bit of syntactic sugar that allows you override args in the args dict when + doing inheritance by simply specifying them as attributes of the parent. The example below + comes from a pixel layout config: + \begin{verbatim} + <PixelConfiguration> + <PixelStrip Id="strip1.1" originLocation="(0,0)" Reverse="True"> + <InheritsFrom>layouts/50PixelStrip.xml</InheritsFrom> + </PixelStrip> + <PixelStrip Id="strip1.2" originLocation="(200,0)"> + <InheritsFrom>layouts/50PixelStrip.xml</InheritsFrom> + </PixelStrip> + \end{verbatim} + + The contents of \texttt{layouts/50PixelStrip.xml} are: + \begin{verbatim} + <PixelStrip> + <Class>layouts.LineLayout</Class> + <Args> + <pixelToPixelSpacing>4</pixelToPixelSpacing> + <spacing>4</spacing> + <numPixels>50</numPixels> + </Args> + </PixelStrip> + \end{verbatim} + + A careful reading of the algorithm will reveal some behaviors which are not specified. What if there are + multiple instances of identical sibling tags? The answer is that this is not currently + supported. It may be supported in the future. + + If you want your tags to be added to an inherited config without trying to merge, put them + in an \texttt{APPEND} tag like so: + + \begin{verbatim} + <Behaviors> + <InheritsFrom>behaviors/StockBehaviors.xml</InheritsFrom> + <APPEND> + <Beavhior> + <InheritsFrom>behaviors/SomethingElse.xml</InerhitsFrom> + </Behavior> + <Behavior> + <Class>blah.blah</Class> + <Args> + </Args> + </Behavior> + </APPEND> + </Behaviors> + \end{verbatim} + \section{Variable Bindings} + SmootConf allows developers to reference other variables within the \texttt{<Args>} tag. These + references are dynamic, and are bound for the lifetime of the object and will updated as + their bound values update. Here is an example: + \begin{verbatim} + <Behavior> + <Class>behaviors.SomeClass</Class> + <Args> + <Id>dimming</Id> + <DecayCoefficient>${DecayTime}$*5</DecayCoefficient> + <DecayTime>10</DecayTime> + </Args> + </Behavior> + \end{verbatim} + In this (fake) example, we bind the DecayCoefficient to the value of DecayTime, which allows us to + set decay in a reasonable unit, decoupled from the coefficient required by the behavior + itself. + + Under the hood, this feature is done with lambda functions. When you query arguments on the + object, the lambda gets resolved (look at \texttt{operationscore/SmootCoreObject.py} for the + implementation of this). Because of this, we also have to ability to go 1 layer deeper. + + Let's say you wanted to operate on another dictionary -- say, the current behavior packet or + and args of another behavior. By surrounding your variable in quotes, querying its value + with product a lambda function, which, when given another dictionary, will resolve the + value. + \begin{verbatim} + <Behavior> + <Class>behaviors.SomeClass</Class> + <Args> + <Id>stayinbounds</Id> + <MaxX>100</MaxX> + <OutOfBounds>'${x}$' < ${MaxX}$</OutOfBounds> + </Args> + </Behavior> + \end{verbatim} + If you call \texttt{self['OutOfBounds']}, and pass it a dictionary with a value at key + \texttt{x}, it will return a boolean stating whether or not \texttt{x > MaxX}. +\end{document} |