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@@ -16,5 +16,65 @@ the project originally started fully in C (which is still the case for the
 \texttt{main} branch) and C++ offers more functionalities that help for a
 smoother development process.
 
+The life-cycle of the simulation was the typical three-step process:
+\begin{enumerate}
+	\item \textbf{State initiation:} the state of the application is set with certain
+	      starting conditions;
+	\item \textbf{State update:} the state, at each frame, gets applied a set of rules that
+	      govern the behaviour of the application;
+	\item \textbf{Termination:} when the user stops the application, it actuates a number
+	      of \texttt{cleaning} up operations.
+\end{enumerate}
+
+Just like any C/C++ project, the modules were split into different files, and
+those modules where themselves split into header files and implementation files.
+The header files expose the public interface which other modules can call to
+execute a determine function, whereas the implementation files, as the name
+suggests, offer the concrete implementation of the aforementioned functions. The
+implementation files can use some static\footnote{static in the sense of C,
+	i.e. visible only to the file it is declared in} functions that it can use
+as auxiliary or utility functions. The header files usually expose the fields
+and methods of the class (or \texttt{struct}) the module is using, if any, together
+with one function for each of three steps of the life-cycle mentioned above.
 
 \subsection{Cairo}
+
+Cairo is a 2D graphics library with support for multiple output devices. Cairo
+is designed to produce consistent output on all output media while taking
+advantage of display hardware acceleration when available. The cairo API
+provides operations similar to the drawing operators of PostScript and PDF.
+Operations in cairo including stroking and filling cubic Bézier splines,
+transforming and compositing translucent images, and antialiased text rendering.
+All drawing operations can be transformed by any affine transformation (scale,
+rotation, shear, etc.). Reading the
+documentation\footnote{\url{https://www.cairographics.org/documentation/}}, and
+more specifically the practical
+tutorial\footnote{\url{https://www.cairographics.org/tutorial/}} was useful to
+understand how the library works.
+
+
+
+The Cairo drawing model relies on a three-layer model, any drawing process takes
+place in three steps:
+
+\begin{minipage}{.5\textwidth}
+	\begin{enumerate}
+		\item first a mask is created, which includes one or more vector
+		      primitives or forms, i.e., circles, squares, TrueType fonts, Bézier
+		      curves, etc;
+
+		\item then source must be defined, which may be a color, a color
+		      gradient, a bitmap or some vector graphics, and from the painted
+		      parts of this source a die cut is made with the help of the above
+		      defined mask;
+
+		\item finally the result is transferred to the destination or surface,
+		      which is provided by the back-end for the output.
+	\end{enumerate}
+\end{minipage}
+\begin{minipage}{.49\textwidth}
+	\centering
+	\includegraphics[width=0.8\textwidth]{cairo}
+	\captionof{figure}{Cairo's drawing model}
+	\label{fig:cairo}
+\end{minipage}