From: David Gow Date: Mon, 7 Apr 2014 03:49:44 +0000 (+0800) Subject: David's lit notes, LaTeXiFiEd X-Git-Url: https://git.ucc.asn.au/?a=commitdiff_plain;h=e7fe600f8846251398682d00d3e3a881e9565b7d;p=ipdf%2Fdocuments.git David's lit notes, LaTeXiFiEd --- diff --git a/LiteratureNotes.pdf b/LiteratureNotes.pdf index 8760bb2..f5b15bd 100644 Binary files a/LiteratureNotes.pdf and b/LiteratureNotes.pdf differ diff --git a/LiteratureNotes.tex b/LiteratureNotes.tex index 6dfa524..39cb258 100644 --- a/LiteratureNotes.tex +++ b/LiteratureNotes.tex @@ -258,6 +258,127 @@ Proves with maths, that rounding errors mean that you need at least $q$ bits for \end{itemize} +%%%% +% David's Stuff +%%%% +\section{Compositing Digital Images\cite{porter1984compositing}} + + + +Perter and Duff's classic paper "Compositing Digital Images" lays the +foundation for digital compositing today. By providing an "alpha channel," +images of arbitrary shapes — and images with soft edges or sub-pixel coverage +information — can be overlayed digitally, allowing separate objects to be +rasterized separately without a loss in quality. + +Pixels in digital images are usually represented as 3-tuples containing +(red component, green component, blue component). Nominally these values are in +the [0-1] range. In the Porter-Duff paper, pixels are stored as $(R,G,B,\alpha)$ +4-tuples, where alpha is the fractional coverage of each pixel. If the image +only covers half of a given pixel, for example, its alpha value would be 0.5. + +To improve compositing performance, albeit at a possible loss of precision in +some implementations, the red, green and blue channels are premultiplied by the +alpha channel. This also simplifies the resulting arithmetic by having the +colour channels and alpha channels use the same compositing equations. + +Several binary compositing operations are defined: +\begin{itemize} +\item over +\item in +\item out +\item atop +\item xor +\item plus +\end{itemize} + +The paper further provides some additional operations for implementing fades and +dissolves, as well as for changing the opacity of individual elements in a +scene. + +The method outlined in this paper is still the standard system for compositing +and is implemented almost exactly by modern graphics APIs such as \texttt{OpenGL}. It is +all but guaranteed that this is the method we will be using for compositing +document elements in our project. + +\section{Bresenham's Algorithm: Algorithm for computer control of a digital plotter\cite{bresenham1965algorithm}} +Bresenham's line drawing algorithm is a fast, high quality line rasterization +algorithm which is still the basis for most (aliased) line drawing today. The +paper, while originally written to describe how to control a particular plotter, +is uniquely suited to rasterizing lines for display on a pixel grid. + +Lines drawn with Bresenham's algorithm must begin and end at integer pixel +coordinates, though one can round or truncate the fractional part. In order to +avoid multiplication or division in the algorithm's inner loop, + +The algorithm works by scanning along the long axis of the line, moving along +the short axis when the error along that axis exceeds 0.5px. Because error +accumulates linearly, this can be achieved by simply adding the per-pixel +error (equal to (short axis/long axis)) until it exceeds 0.5, then incrementing +the position along the short axis and subtracting 1 from the error accumulator. + +As this requires nothing but addition, it is very fast, particularly on the +older CPUs used in Bresenham's time. Modern graphics systems will often use Wu's +line-drawing algorithm instead, as it produces antialiased lines, taking +sub-pixel coverage into account. Bresenham himself extended this algorithm to +produce Bresenham's circle algorithm. The principles behind the algorithm have +also been used to rasterize other shapes, including B\'{e}zier curves. + +\section{Quad Trees: A Data Structure for Retrieval on Composite Keys\cite{finkel1974quad}} + +This paper introduces the ``quadtree'' spatial data structure. The quadtree structure is +a search tree in which every node has four children representing the north-east, north-west, +south-east and south-west quadrants of its space. + +\section{Xr: Cross-device Rendering for Vector Graphics\cite{worth2003xr}} + +Xr (now known as Cairo) is an implementation of the PDF v1.4 rendering model, +independent of the PDF or PostScript file formats, and is now widely used +as a rendering API. In this paper, Worth and Packard describe the PDF v1.4 rendering +model, and their PostScript-derived API for it. + +The PDF v1.4 rendering model is based on the original PostScript model, based around +a set of \emph{paths} (and other objects, such as raster images) each made up of lines +and B\'{e}zier curves, which are transformed by the ``Current Transformation Matrix.'' +Paths can be \emph{filled} in a number of ways, allowing for different handling of self-intersecting +paths, or can have their outlines \emph{stroked}. +Furthermore, paths can be painted with RGB colours and/or patterns derived from either +previously rendered objects or external raster images. +PDF v1.4 extends this to provide, amongst other features, support for layering paths and +objects using Porter-Duff compositing\cite{porter1984compositing}, giving each painted path +the option of having an $\alpha$ value and a choice of any of the Porter-Duff compositing +methods. + +The Cairo library approximates the rendering of some objects (particularly curved objects +such as splines) with a set of polygons. An \texttt{XrSetTolerance} function allows the user +of the library to set an upper bound on the approximation error in fractions of device pixels, +providing a trade-off between rendering quality and performance. The library developers found +that setting the tolerance to greater than $0.1$ device pixels resulted in errors visible to the +user. + +\section{Glitz: Hardware Accelerated Image Compositing using OpenGL\cite{nilsson2004glitz}} + +This paper describes the implementation of an \texttt{OpenGL} based rendering backend for +the \texttt{Cairo} library. + +The paper describes how OpenGL's Porter-Duff compositing is easily suited to the Cairo/PDF v1.4 +rendering model. Similarly, traditional OpenGL (pre-version 3.0 core) support a matrix stack +of the same form as Cairo. + +The ``Glitz'' backend will emulate support for tiled, non-power-of-two patterns/textures if +the hardware does not support it. + +Glitz can render both triangles and trapezoids (which are formed from pairs of triangles). +However, it cannot guarantee that the rasterization is pixel-precise, as OpenGL does not proveide +this consistently. + +Glitz also supports multi-sample anti-aliasing, convolution filters for raster image reads (implemented +with shaders). + +Performance was much improved over the software rasterization and over XRender accellerated rendering +on all except nVidia hardware. However, nVidia's XRender implementation did slow down significantly when +some transformations were applied. + \pagebreak diff --git a/ProjectProposalDavid.pdf b/ProjectProposalDavid.pdf index 6c3f16e..f2ece22 100644 Binary files a/ProjectProposalDavid.pdf and b/ProjectProposalDavid.pdf differ diff --git a/ProjectProposalSam.pdf b/ProjectProposalSam.pdf index 7cc5d2f..0549d9a 100644 Binary files a/ProjectProposalSam.pdf and b/ProjectProposalSam.pdf differ diff --git a/papers.bib b/papers.bib index c4a857c..e2aa0e9 100644 --- a/papers.bib +++ b/papers.bib @@ -16,6 +16,39 @@ year={2006} } +%%%%%%%%%%%%%%%%%%%%%%%% +% Basic Rendering Theory +%%%%%%%%%%%%%%%%%%%%%%%% + +%Porter-Duff compositing. +% Keith Packard has a really nice PDF version of this. +@inproceedings{porter1984compositing, + title={Compositing digital images}, + author={Porter, Thomas and Duff, Tom}, + booktitle={ACM Siggraph Computer Graphics}, + volume={18}, + number={3}, + pages={253--259}, + year={1984}, + organization={ACM} +} + +%Bresenham's Line Drawing Algorithm +% See Michael Abrash's Graphics Programming Black Book for a +% much better guide to implementing this (at least on the 486) +@article{bresenham1965algorithm, + title={Algorithm for computer control of a digital plotter}, + author={Bresenham, Jack E}, + journal={IBM Systems journal}, + volume={4}, + number={1}, + pages={25--30}, + year={1965}, + publisher={IBM Corp.} +} + + + %%%%%%%%%%%%%%%%%%%%%%% % Floating-pt Precision %%%%%%%%%%%%%%%%%%%%%%% @@ -209,6 +242,21 @@ Goldberg:1991:CSK:103162.103163, organization={IEEE} } +%%%%%%%%%%%%%%%%% +% Quadtrees +%%%%%%%%%%%%%%%%% +@article{finkel1974quad, + title={Quad trees a data structure for retrieval on composite keys}, + author={Finkel, Raphael A. and Bentley, Jon Louis}, + journal={Acta informatica}, + volume={4}, + number={1}, + pages={1--9}, + year={1974}, + publisher={Springer} +} + + % Basic overview of PDF and how it is awesome. % This doesn't seem like a major revelation for 2002 @article{cheng2002portable, diff --git a/references/finkle1974quad.pdf b/references/finkle1974quad.pdf new file mode 100644 index 0000000..d3ae073 Binary files /dev/null and b/references/finkle1974quad.pdf differ