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