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Thomas Forgione
2019-10-01 17:34:05 +02:00
parent 9536bf1c25
commit 947a32d970
8 changed files with 68 additions and 61 deletions
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22
src/foreword/3d-model.tex
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@@ -8,55 +8,55 @@ A 3D model consists in a set of data.
\begin{itemize}
\item \textbf{Vertices} are simply 3D points;
\item \textbf{Faces} are polygons defined from vertices (most of the time, they are triangles);
\item \textbf{Textures} are images that can be applied to faces;
\item \textbf{Textures} are images that can be use to paint faces to add visual richness;
\item \textbf{Texture coordinates} are information added to a face to describe how the texture should be applied on a face;
\item \textbf{Normals} are 3D vectors that can give information about light behaviour on a face.
\end{itemize}
The Wavefront OBJ is probably the best format to give an example of 3D model since it describes all these elements in text format.
The Wavefront OBJ is one of the most popular format and describes all these elements in text format.
A 3D model encoded in the OBJ format typically consists in two files: the materials file (\texttt{.mtl}) and the object file (\texttt{.obj}).
\paragraph{}
The materials file declare all the materials that the object file will reference.
Each material has a name, and can have photometric properties such as ambient, diffuse and specular colors, as well as texture maps.
A material consists in name, and other photometric properties such as ambient, diffuse and specular colors, as well as texture maps.
Each face correspond to a material and a renderer can use the material's information to render the faces.
A simple material file is visible on Listing~\ref{i:mtl}.
\paragraph{}
The object file declare the 3D content of the objects.
The object file declares the 3D content of the objects.
It declares vertices, texture coordinates and normals from coordinates (e.g.\ \texttt{v 1.0 2.0 3.0} for a vertex, \texttt{vt 1.0 2.0} for a texture coordinate, \texttt{vn 1.0 2.0 3.0} for a normal).
These elements are numbered starting from 1.
Faces are declared by using the indices of these elements. A face is a polygon with any number of vertices and can be declared in multiple manners:
\begin{itemize}
\item \texttt{f 1 2 3} defines a triangle face that joins the first, the second and the third vertex declared;
\item \texttt{f 1/1 2/3 3/4} defines a triangle similar but with texture coordinates, the first texture coordinate is associated to the first vertex, the third texture coordinate is associated to the second vertex, and the fourth texture coordinate is associated with the third vertex;
\item \texttt{f 1//1 2//3 3//4} defines a triangle similar but using normal instead of texture coordinates;
\item \texttt{f 1/1 2/3 3/4} defines a similar triangle but with texture coordinates, the first texture coordinate is associated to the first vertex, the third texture coordinate is associated to the second vertex, and the fourth texture coordinate is associated with the third vertex;
\item \texttt{f 1//1 2//3 3//4} defines a similar triangle but using normals instead of texture coordinates;
\item \texttt{f 1/1/1 2/3/3 3/4/4} defines a triangle with both texture coordinates and normals.
\end{itemize}
It can include materials from a material file (\texttt{mtllib path.mtl}) and apply the materials that it declares to faces.
An object file can include materials from a material file (\texttt{mtllib path.mtl}) and apply the materials that it declares to faces.
A material is applied by using the \texttt{usemtl} keyword, followed by the name of the material to use.
The faces declared after a \texttt{usemtl} are painted using the material in question.
An example of object file is visible on Listing~\ref{i:obj}.
\begin{figure}[th]
\centering
\begin{subfigure}[b]{0.4\textwidth}
\begin{subfigure}[c]{0.4\textwidth}
\lstinputlisting[
language=XML,
caption={An object file describing a cube},
label=i:obj,
]{assets/introduction/cube.obj}
\end{subfigure}\quad%
\begin{subfigure}[b]{0.4\textwidth}
\begin{subfigure}[c]{0.4\textwidth}
\lstinputlisting[
language=XML,
caption={A material file describing a material},
label=i:mtl,
]{assets/introduction/materials.mtl}
\vspace{0.2cm}
\includegraphics[width=\textwidth]{assets/introduction/cube.png}
\caption*{A rendering of the cube}
\captionof{figure}{A rendering of the cube}
\end{subfigure}
\caption{The OBJ representation of a cube and its render\label{i:cube}}
\end{figure}

40
src/foreword/video-vs-3d.tex
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@@ -3,7 +3,7 @@
\section{Similarities and differences between video and 3D\label{i:video-vs-3d}}
Contrary to what one might think, the video streaming scenario and the 3D streaming one share many similarities: at a higher level of abstraction, they are both systems that allow a user to access remote content without having to wait until everything is loaded.
Analyzing the similarities and the differences between the video and the 3D scenarios as well as having knowledge about video streaming litterature is\todo{is key or are key?} key to developing an efficient 3D streaming system.
Analyzing the similarities and the differences between the video and the 3D scenarios as well as having knowledge about video streaming litterature is~\todo{is key or are key?} key to developing an efficient 3D streaming system.
\subsection{Data persistence}
@@ -40,7 +40,7 @@ In both cases, an algorithm for content streaming has to acknowledge those diffe
In video streaming, most of the data (in terms of bytes) is used for images.
Thus, the most important thing a video streaming system should do is optimize the image streaming.
That's why, on a video on Youtube for example, there may be 6 resolutions for images (144p, 240p, 320p, 480p, 720p and 1080p) but only 2 resolutions for sound.
This is one of the main differences between video and 3D streaming: in a 3D scene, the geometry and the texture size are approximately the same, and work to improve the streaming needs to be performed on both.
This is one of the main differences between video and 3D streaming: in a 3D scene, geometry and texture sizes are approximately the same, and leveraging between those two types of content is a key problem.
\subsection{Chunks of data}
@@ -51,9 +51,9 @@ In mesh streaming, it can either by segmenting faces in chunks, with a certain n
\subsection{Interaction}
The ways of interacting with the content is probably the most important difference between video and 3D.
In a video interface, there is only one degree of freedom: the time.
In a video interface, there is only one degree of freedom: time.
The only thing a user can do is let the video play itself, pause or resume it, or jump to another moment in the video.
Even though these interactions seem easy to handle, giving the best possible experience to the user is already challenging. For example, to perform these few actions, Youtube gives the user multiple options.
Even though these interactions seem easy to handle, giving the best possible experience to the user is already challenging. For example, to perform these few actions, Youtube provides the user with multiple options.
\begin{itemize}
@@ -66,7 +66,7 @@ Even though these interactions seem easy to handle, giving the best possible exp
\item To navigate to another moment of the video, the user can:
\begin{itemize}
\item click the timeline of the video where he wants;
\item click the timeline of the video where they wants;
\item press the left arrow key to move 5 seconds backwards;
\item press the right arrow key to move 5 seconds forwards;
\item press the \texttt{J} key to move 10 seconds backwards;
@@ -84,7 +84,7 @@ All the interactions are summmed up in Figure~\ref{i:youtube-keyboard}.
\newcommand{\playpausecontrol}{Pink}
\newcommand{\othercontrol}{PalePaleGreen}
\newcommand{\keystrokescale}{0.55}
\newcommand{\keystrokescale}{0.625}
\newcommand{\tuxlogo}{\FA\symbol{"F17C}}
\newcommand{\keystrokemargin}{0.1}
\newcommand{\keystroke}[5]{%
@@ -245,27 +245,27 @@ All the interactions are summmed up in Figure~\ref{i:youtube-keyboard}.
% Legend
\begin{tikzpicture}[scale=\keystrokescale]
\keystrokebg{7}{8}{-6}{-5}{}{\absoluteseekcontrol};
\node[right=0.2cm] at (7.5, -5.55) {Absolute seek keys};
\keystrokebg{0}{1}{0}{1}{}{\absoluteseekcontrol};
\node[right=0.3cm] at (0.5, 0.5) {\small Absolute seek keys};
\keystrokebg{7}{8}{-7}{-6}{}{\relativeseekcontrol};
\node[right=0.2cm] at (7.5, -6.55) {Relative seek keys};
\keystrokebg{6}{7}{0}{1}{}{\relativeseekcontrol};
\node[right=0.3cm] at (6.5, 0.5) {\small Relative seek keys};
\keystrokebg{7}{8}{-8}{-7}{}{\playpausecontrol};
\node[right=0.2cm] at (7.5, -7.55) {Play or pause keys};
\keystrokebg{12}{13}{0}{1}{}{\playpausecontrol};
\node[right=0.3cm] at (12.5, 0.5) {\small Play or pause keys};
\keystrokebg{7}{8}{-9}{-8}{}{\othercontrol};
\node[right=0.2cm] at (7.5, -8.55) {Other keys};
\keystrokebg{18}{19}{0}{1}{}{\othercontrol};
\node[right=0.3cm] at (18.5, 0.5) {\small Other keys};
\end{tikzpicture}
\caption{Youtube shortcuts\label{i:youtube-keyboard}}
\caption{Youtube shortcuts (white keys are unused)\label{i:youtube-keyboard}}
\end{figure}
Those interactions are different if the user is using a mobile device.
\begin{itemize}
\item To pause a video, the user must touch the screen once to make the HUD appear and once on the pause button at the center of the screen.
\item To pause a video, the user must touch the screen once to make the timeline and the buttons appear and once on the pause button at the center of the screen.
\item To resume a video, the user must touch the play button at the center of the screen.
\item To navigate to another moment of the video, the user can:
\begin{itemize}
@@ -278,16 +278,16 @@ When it comes to 3D, there are many approaches to manage user interaction.
Some interfaces mimic the video scenario, where the only variable is the time and the camera follows a predetermined path on which the user has no control.
These interfaces are not interactive, and can be frustrating to the user who might feel constrained.
Some other interfaces add 2 degrees of freedom to the previous one: the user does not control the position of the camera but he can control the angle. This mimics the scenario of the 360 video.
Some other interfaces add 2 degrees of freedom to the previous one: the user does not control the position of the camera but they can control the angle. This mimics the scenario of the 360 video.
Finally, most of the other interfaces give at least 5 degrees of freedom to the user: 3 being the coordinates of the position of the camera, and 2 being the angle (assuming the up vector is unchangeable, some interfaces might allow that giving a sixth degree of freedom).
\subsection{Relationship between interface, interaction and streaming}
In both video and 3D systems, streaming affects the interaction.
For example, in a video streaming scenario, if a user sees that the video is fully loaded, he might start moving around on the timeline, but if he sees that the streaming is just enough to not stall, he might prefer staying peaceful and just watch the video.
If the streaming stalls for too long, the user migth seek somewhere else hoping for the video to resume, or totally give up and leave the video.
The same types of behaviour occur in 3D streaming: if a user is somewhere in a scene, and sees more data appearing, he might wait until enough data has arrived, but if he sees nothing happens, he might leave to look for data somewhere else.
For example, in a video streaming scenario, if a user sees that the video is fully loaded, they might start moving around on the timeline, but if they sees that the streaming is just enough to not stall, they might prefer staying peaceful and just watch the video.
If the streaming stalls for too long, the user migth seek somewhere else hoping for the video to resume, or get frustrated and leave the video.
The same types of behaviour occur in 3D streaming: if a user is somewhere in a scene, and sees more data appearing, they might wait until enough data has arrived, but if they sees nothing happens, they might leave to look for data somewhere else.
Those examples show how streaming can affect the interaction, but the interaction also affects the streaming.
In a video streaming scenario, if a user is watching peacefully without interacting, the system just has to request the next chunks of video and display them.