# [cairo-commit] papers/opengl_freenix04 opengl_freenix04.tex, 1.32, 1.33 sinus.png, 1.2, NONE

David Reveman commit at pdx.freedesktop.org
Thu Mar 18 07:50:17 PST 2004

Committed by: davidr

Update of /cvs/cairo/papers/opengl_freenix04
In directory pdx:/tmp/cvs-serv11018

Modified Files:
opengl_freenix04.tex
Removed Files:
sinus.png
Log Message:
Cleaned up AA section

Index: opengl_freenix04.tex
===================================================================
RCS file: /cvs/cairo/papers/opengl_freenix04/opengl_freenix04.tex,v
retrieving revision 1.32
retrieving revision 1.33
diff -C2 -d -r1.32 -r1.33
*** a/opengl_freenix04.tex	16 Mar 2004 21:27:01 -0000	1.32
--- b/opengl_freenix04.tex	18 Mar 2004 15:50:14 -0000	1.33
***************
*** 444,474 ****
Aliasing is a general term used to describe the problems that may
occur whenever an analog signal is point sampled to convert it into
!       a digital signal. It happens whenever an analog signal is not
!       sampled at a high enough frequency. The number of samples don't
!       contain enough information to represent the actual source signal.
!       Instead the samples seem to represent a different signal of lower
!       frequency, called an aliased signal.
!
!       \begin{figure}[htbp]
! 	\begin{centering}
! 	  \epsfig{file=sinus.eps}
! 	  \small\itshape
! 	  \caption{\small\itshape The source signal is sampled into the
! 	    aliased signal below. Information is lost in the process.}
! 	  \label{sinus}
! 	\end{centering}
!       \end{figure}

-       There is a theorem known from point sampling theory called the
-       Nyquist Theorem. It states that in order to avoid aliasing of a
-       sampled signal the sampling rate must be greater than or equal to
-       two times the highest frequency contained in the signal.
-
In computer graphics, aliasing translates to the problems related to
point sampling an analogous mathematical representation of an image into
discrete pixel positions. With the currently available display
!       devices it is simply not feasible to sample a non aliased signal
!       according to Nyquists Theorem. Figure~\ref{jaggies} illustrates an
!       aliased graphical image suffering from a jagged edge.

\begin{figure}[htbp]
--- 444,466 ----
Aliasing is a general term used to describe the problems that may
occur whenever an analog signal is point sampled to convert it into
!       a digital signal, and the sample rate is to low.
!       The number of samples don' contain enough information to represent the
!       actual source signal. Instead the samples seem to represent a different
!       signal of lower frequency, called an aliased signal.

In computer graphics, aliasing translates to the problems related to
point sampling an analogous mathematical representation of an image into
discrete pixel positions. With the currently available display
!       devices it is simply not feasible to sample a non aliased signal,
!       the resolution of the screen (the number of samples) is simply not high
!       enough.
!
!       The results of aliasing are called artifacts, the most common
!       artifacts in computer graphics include jagged profiles,
!       disappearing or improperly rendered fine detail and disintegrating
!       textures. The most obvious one and the one that most applies
!       to 2D graphics is the jagged profile artifact.
!       Figure~\ref{jaggies} illustrates an aliased graphical image suffering
!       from a jagged edge.

\begin{figure}[htbp]
***************
*** 483,500 ****
\end{figure}

-
-       The results of aliasing are called artifacts, the most common
-       artifacts in computer graphics include jagged profiles,
-       disappearing or improperly rendered fine detail and disintegrating
-       textures.
-
Anti-aliasing, naturally enough, is the name for techniques designed
to reduce or eliminate this effect, usually by shading the pixels
!       along the borders of graphical elements. A simple theoretical model
!       for anti-aliasing pretends that rendering takes place by averaging
!       the image that would be produced on an infinite-resolution device.
!       It turns out that this is by no means the best method, but there are
!       several techniques that can be used to achieve anti-aliased graphics
!       rendering with the OpenGL API. The most common techniques include;

\begin{itemize}
--- 475,483 ----
\end{figure}

Anti-aliasing, naturally enough, is the name for techniques designed
to reduce or eliminate this effect, usually by shading the pixels
!       along the borders of graphical elements. There are several techniques
!       that can be used to achieve anti-aliased graphics rendering with the
!       OpenGL API. The most common techniques include;

\begin{itemize}
***************
*** 531,539 ****

The chosen techniques are supported in most consumer level graphics
!       hardware
!       since at least three graphic card generations back. As \libname{}
!       already needs other relatively new features e.g pbuffer support to
!       provide full functionality these latest generations of graphics
!       hardware is the group of users already targeted.

Full-scene anti-aliasing using hardware assist is typically
--- 514,521 ----

The chosen techniques are supported in most consumer level graphics
!       hardware since at least three graphic card generations back.
!       As \libname{} already needs other relatively new features e.g
!       pbuffer support to provide full functionality these latest generations
!       of graphics hardware belong to the group of users already targeted.

Full-scene anti-aliasing using hardware assist is typically
***************
*** 547,558 ****
affect the choice in this case however, as anti-aliasing of text will
preferably be handled by the external font rendering library.
!       On high end
!       systems this technique has potential for generating extremely high
!       quality results with a relatively low cost. Unfortunately it is not
always available for offscreens (pbuffers).
!       This means problems with indirect polygon
!       rendering as polygons are then drawn to intermediate offscreen surfaces.
!       This technique will be used on all rendering operations if available,
!       direct as well as indirect.

OpenGL's built in polygon smooth hint is perhaps the most common
--- 529,538 ----
affect the choice in this case however, as anti-aliasing of text will
preferably be handled by the external font rendering library.
!       On high end systems this technique has potential for generating extremely
!       high quality results with a relatively low cost. Unfortunately it is not
always available for offscreens (pbuffers).
!       This means problems with indirect polygon rendering as polygons are then
!       drawn to intermediate offscreen surfaces. This technique will be used on
!       all rendering operations if available, direct as well as indirect.

OpenGL's built in polygon smooth hint is perhaps the most common
***************
*** 900,904 ****
X11 & XFree86 4.3.0 \\
\hline
!         GPU & NVIDIA GeForce FX-5600 (using NVIDIA's binary driver) \\
\end{tabular}
\end{footnotesize}
--- 880,884 ----
X11 & XFree86 4.3.0 \\
\hline
!         GPU & NVIDIA GeForce FX-5600 (NVIDIA's binary driver) \\
\end{tabular}
\end{footnotesize}
***************
*** 949,953 ****
\end{footnotesize}
\caption{\small\itshape Seconds to complete composite test
!                               (lower is better))}
\label{rendermark1}
\end{table}
--- 929,933 ----
\end{footnotesize}
\caption{\small\itshape Seconds to complete composite test
!                               (lower is better)}
\label{rendermark1}
\end{table}

--- sinus.png DELETED ---