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| author | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
|---|---|---|
| committer | Graeme Geldenhuys <graeme@mastermaths.co.za> | 2012-03-19 11:58:09 +0200 |
| commit | 90ae43f347fe4075f76a5f37d011d39bd4c10ddd (patch) | |
| tree | a04fa64e893f21a07ed19704121e626877f4aef6 /docs/aggpas/introduction.agdoc.html | |
| parent | 88f1fc9acda900eecfcfc884a60e4958145e3fc0 (diff) | |
| download | fpGUI-90ae43f347fe4075f76a5f37d011d39bd4c10ddd.tar.xz | |
adds AGG docs in general.
These docs give you lots of background information on the working
of the AGG (Anti-Grain Geometry) library and how it works.
Using the knowledge you learn from this, you will be able to extend
the TAgg2D canvas for your own needs and applications.
Diffstat (limited to 'docs/aggpas/introduction.agdoc.html')
| -rw-r--r-- | docs/aggpas/introduction.agdoc.html | 690 |
1 files changed, 690 insertions, 0 deletions
diff --git a/docs/aggpas/introduction.agdoc.html b/docs/aggpas/introduction.agdoc.html new file mode 100644 index 00000000..c26ea581 --- /dev/null +++ b/docs/aggpas/introduction.agdoc.html @@ -0,0 +1,690 @@ +<html><head><title>Anti-Grain Geometry - Introduction</title> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<link rel="stylesheet" type="text/css" +href="introduction.agdoc_files/agg.css"> +</head><body><a name="PAGE_INTRODUCTION"><b></b></a> + + +<table style="margin: 0px;" height="1px" width="640px" border="0" +cellpadding="0" cellspacing="0"> +<tbody><tr> +<td bgcolor="#583927"></td> +</tr> +</tbody></table> +<table style="margin: 0px;" width="640px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr> +<td> +<table style="margin: 0px;" width="170px" border="0" cellpadding="0" +cellspacing="0"> +<tbody><tr><td><a href="http://www.antigrain.com/index.html" +class="mpmenu">Home/</a></td></tr> +<tr><td><a href="http://www.antigrain.com/doc/index.html" class="mpmenu">Table + of Content/</a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +<tr><td><a href="" class="mpmenu"></a></td></tr> +</tbody></table> +</td> +<td width="1px" bgcolor="#583927"></td> +<td style="text-align: right;" valign="top" width="450px"> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr> +<td><img src="introduction.agdoc_files/agg_logo.gif" border="0"></td> +</tr> +<tr> +<td> +<table style="margin: 0px;" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr height="15px"> +<td> <a class="topmenu" +href="http://www.antigrain.com/news/index.html">News</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/doc/index.html">Docs</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/download/index.html">Download</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/maillist/index.html">Mailing List</a> </td> +<td width="1px" bgcolor="#8e521d"></td> +<td> <a class="topmenu" +href="http://www.antigrain.com/cvs/index.html">CVS</a> </td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +</td> +</tr> +</tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p> +</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td><h1>Introduction<span +class="subtitle"><br>Overview and Basic Concepts</span></h1></td></tr></tbody></table> + + +<table class="toc" width="640px"><tbody><tr><td> + <div style="margin-left: 2em; padding: 3px; font-size: 14px;"><a +href="#toc0001"><b>Brief Overview</b></a> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0002">Yet Another Invention of the Wheel</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0003">Gentle Criticism</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0004">The Proposal</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0005">Anti-Aliasing and Subpixel Accuracy</a></div></div> + <div style="margin-left: 2em; padding: 3px; font-size: 14px;"><a +href="#toc0006"><b>Basic Concepts</b></a> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0007">Design of the Library</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0008">Colors, Color Spaces, and Pixel Formats</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0009">Coordinate Units</a></div> + <div style="margin-left: 2em; font-size: 12px;"><a +href="#toc0010">AGG Building and Coding Notes</a></div></div> + <div style="margin-left: 2em; padding: 3px; font-size: 14px;"><a +href="#toc0011"><b>About this Manual</b></a></div> + +</td></tr></tbody></table> + + +<h2>Brief Overview<a name="toc0001"></a></h2> + + +<h3>Yet Another Invention of the Wheel<a name="toc0002"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Grain</nobr> + Geometry</b> (<b>AGG</b>) is a general purpose graphical toolkit +written completely in +standard and platform independent <b>C++</b>. +It can be used in many areas of computer programming where high quality +2D +graphics is an essential part of the project. For example, if you render + +2D geographic maps <b>AGG</b> is a must. <b>AGG</b> uses only <b>C++</b> + and standard +C runtime functions, such as <b>memcpy, sin, cos, sqrt</b>, etc. +The basic algorithms don't even use <b>C++ Standard Template Library</b>. + Thus, <b>AGG</b> can be used in a very large +number of applications, including embedded systems.</p></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>On +the other hand, <b>AGG</b> allows you to replace any part of the +library, if, for example, +it doesn't fit performance requirements. Or you can add another color +space if needed. +All of it is possible because of extensive using of <b>C++</b> <b>template</b> + mechanism.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Grain</nobr> + Geometry</b> is not a solid graphic library and it's not very easy to +use. +I consider <b>AGG</b> as a <b>“tool to create other tools”</b>. It means + that there's +no <b>“Graphics”</b> object or something like that, instead, <b>AGG</b> +consists of +a number of loosely coupled algorithms that can be used together or +separately. +All of them have well defined interfaces and absolute minimum of +implicit or explicit +dependencies.</p></td></tr></tbody></table> + + + +<h3>Gentle Criticism<a name="toc0003"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Most + of the graphic libraries have a single class like <b>“Graphics”</b> +in GDI+, that has hundred or even thousands of functions. This object +can exist implicitly, like in OpenGL. Anyway, all commonly used +graphical tool kits, including Java2D, DisplayPDF, SVG, and other very +good ones have this kind of a class explicitly or implicitly. +That's simple and in some cases quite suitable, but always very +restrictive. It works well only in simple cases, at least I haven't +seen a graphical library that would completely fit all my needs. +Moreover, all that kinds of libraries or standards have a +syndrome of giantism. Most of the functionality is never +used, but some simple things are impossible to achieve. Herein, the +graphical engines (or libraries) typically weigh tons of +mega-bytes. If you take the most advanced SVG viewer, +<a href="http://www.adobe.com/svg/main.html"><img +src="introduction.agdoc_files/link.gif" border="0">Adobe SVG</a>, it +works well only with +simplest primitives. As soon as you try to use some advanced things, +like interactive SVG with different graphical filters, you will have +memory leaks, or even crashes. It's not because it has bad design, +it's because the proposed possibilities assume extremely complex design. +The design itself becomes an <b>NP-complete</b> task, which is +impossible +to perceive by a human mind as impossible to perceive the infinity.</p></td></tr></tbody></table> + + + +<h3>The Proposal<a name="toc0004"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The +primary goal of <b><nobr>Anti-Grain</nobr> Geometry</b> is to break this + ancient as mammoth's manure +tradition and show you the beauty of stability, lightness, +flexibility, and freedom. The basic concepts can seem not very +conventional at the beginning, but they are very close to the ones +used in <b>STL</b>. But there's a big difference too. <b>STL</b> is a +general <b>C++</b> tool +while <b>AGG</b> is <b>C++</b> graphics. You usually use <b>STL</b> in +your applications directly +as a convenient toolkit. I wouldn't say it's a good idea to use <b>AGG</b> + in the +very same way. A good idea is to create a +lightweight, problem oriented wrapper over <b>AGG</b> to solve your +particular +tasks. How can that be different from that very GDI+ then? The first +thing is that you have total control upon that wrapper. <b><nobr>Anti-Grain</nobr> + Geometry</b> just provides +you a set of basic algorithms and flexible design with the minimum of +implicit +or explitit dependencies. You and only you define the interface, +conversion pipelines, and the form of output. You can even simulate a +part +of any existing graphical interface. For example, you can use <b>AGG</b> + rasterizer +to display graphics on the screen and direct Windows GDI calls for +printing, +incorporating it into a single API. Not convincing? Look at the quality +of +rendering in <b>GDI+</b> and <b>AGG</b>: +</p></td></tr></tbody></table><a name="GDIP_AGG_QUALITY"><b></b></a><table + width="640px"><tbody><tr><td><center><img +src="introduction.agdoc_files/qual_gdip_agg.gif" title="Quality of +Rendering" border="0"><br><i>Quality of Rendering</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>But +most of all, your applications become absolutely portable, if +your design is smart enough. <b>AGG</b> can be also a tool to combine +different +outputs in a uniform API. Particularly, you can use <b>AGG</b> to +generate +raster images on the server side in your Web-Based applications. And it +all +can be <b>cross-platform!</b></p></td></tr></tbody></table> + + + +<a name="PAGE_ANTI_ALIASING"><b></b></a> +<h3>Anti-Aliasing and Subpixel Accuracy<a name="toc0005"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Aliasing</nobr></b> + is a very well known technique used to improve the visual quality of +images when displaying them on low resolution devices. It's based on the + properties +of the human vision. Look at the following picture and try to guess what + it means. +</p></td></tr></tbody></table><table width="640px"><tbody><tr><td><center><img + src="introduction.agdoc_files/stereo_enlarged.gif" title="" border="0"><br><i></i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Well, + it's a word drawn with <b><nobr>Anti-Aliasing</nobr></b>. In terms of +Kotelnikov-Shannon's theorem, +the maximal frequency of the image is far above of the Shannon limit.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><img + src="introduction.agdoc_files/stereo_small.gif" title="" +style="border-color: rgb(255, 255, 255);" align="left" border="4"><!----> + +Now look at the same picture that has normal size and <b>within the +context</b>. You easily +recognize word <b>“stereo”</b>. However, the pictrures are exactly the +same. The first +one is just an enlarged version of the last one. This very property +allows us to +reconstruct missing information on the basis of accumulated experience. <b><nobr>Anti-Aliasing</nobr></b> + +doesn't make you see better, it basically makes you brain work better +and reconstruct +missing details. The result is great. It allows us to draw much more +detailed maps for +example.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>But +the point is not only in <b><nobr>Anti-Aliasing</nobr></b> itself. The +point is we can draw primitives +with <b>Subpixel Accuracy</b>. It's especially important for the visual +thickness of the lines. +First, let us see that even with simple Bresenham line interpolator we +can achieve +a better result if we use <b>Subpixel Accuracy</b>. The following +picture shows enlarged +results of the simple Bresenham interpolator. +</p></td></tr></tbody></table><a name="SUBPIXEL_BRESENHAM"><b></b></a><table + width="640px"><tbody><tr><td><center><img +src="introduction.agdoc_files/subpixel_bresenham.gif" title="A Bresenham + Line Rendered with Subpixel Accuracy" border="0"><br><i>A Bresenham +Line Rendered with Subpixel Accuracy</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Consider + cases (2) and (3). The thin black lines are what we need to +interpolate. +If we use <b>Subpixel Accuracy</b> we will really have two different +sets of pixels +displayed, despite of the fact that the begins and ends of both lines +fall into +the same pixels. And the lines have really different tangents, which is +very important. +If we use a classical Bresenham, without considering the <b>Subpixel +Accuracy</b> we will see +result (1) in all cases. That's especially important to approximate +curves with short +line segments. But if we use <b><nobr>Anti-Aliasing</nobr></b> plus <b>Subpixel + Accuracy</b> we can do much better. +Look at that difference. +</p></td></tr></tbody></table><table width="640px"><tbody><tr><td +style="text-align: center;"><p> +<img src="introduction.agdoc_files/aliased_pix_accuracy.gif" title="" +border="0"><!----> +<img src="introduction.agdoc_files/aliased_subpix_accuracy.gif" title="" + border="0"><!----> +<img src="introduction.agdoc_files/anti_aliased.gif" title="" border="0"><!----> +</p></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Here + all three spirals are approximated with short straight line segments. +The left one is drawn using regular integer Bresenham, when the +coordinates +are rounded off to pixels (you will have a similar result if you use +Winwows GDI MoveTo/LineTo, for example). The one in the middle uses a +modified +integer Bresenham with precision of 1/256 of a pixel. And the right one +uses +the same 1/256 accuracy, but with <b><nobr>Anti-Aliasing</nobr></b>. +Note that it's very important +to have a possibility of real subpixel positioning of the line segments. + +If we use regular pixel coordinates with <b><nobr>Anti-Aliasing</nobr></b>, + the spiral will look +smooth but still, as ugly as the one on the left.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>The <b>Subpixel + Accuracy</b> is even more important to control the visual thickness +of the lines. It's possible only if we have good algorithms of +<b><nobr>Anti-Aliasing</nobr></b>. On the other hand, there's no much +sense of <b><nobr>Anti-Aliasing</nobr></b> +if can set the line width with the discretness of one pixel only. <b><nobr>Anti-Aliasing</nobr></b> +and <b>Subpixel Accuracy</b> always work in cooperation.</p></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Modern + displays have resolutions of at most 120 DPI, while <b>Subpixel +Accuracy</b> +is actual up to 300 DPI. The following picture shows lines with +thickness +starting from 0.3 pixels and increasing by 0.3 pixel. +</p></td></tr></tbody></table><a name="LINE_THICKNESS"><b></b></a><table + width="640px"><tbody><tr><td><center><img +src="introduction.agdoc_files/line_thickness.gif" title="Lines Rendered +with Anti-Aliasing and Subpixel Accuracy" border="0"><br><i>Lines +Rendered with Anti-Aliasing and Subpixel Accuracy</i></center></td></tr></tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>There + are two more examples of rendering with <b>Subpixel Accuracy</b>.</p></td></tr></tbody></table> + +<a name="SUBPIXEL_ACCURACY1"><b></b></a><table width="640px"><tbody><tr><td><center><img + src="introduction.agdoc_files/subpixel_accuracy1.gif" title="Circles +Rendered with Anti-Aliasing and Subpixel Accuracy" border="0"><br><i>Circles + Rendered with Anti-Aliasing and Subpixel Accuracy</i></center></td></tr></tbody></table> +<table style="margin: 0px;" height="1px" width="640px" bgcolor="#583927" + border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<a name="SUBPIXEL_ACCURACY2"><b></b></a><table width="640px"><tbody><tr><td><center><img + src="introduction.agdoc_files/subpixel_accuracy2.gif" title="Cute +Lions" border="0"><br><i>Cute Lions</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Note + that the appearance of the small ones remains consistent +despite of lost details. +</p></td></tr></tbody></table><table style="margin: 0px;" height="1px" +width="640px" bgcolor="#583927" border="0" cellpadding="0" +cellspacing="0"><tbody><tr><td></td></tr></tbody></table> + + + + +<br><h2>Basic Concepts<a name="toc0006"></a></h2> + + + + +<h3>Design of the Library<a name="toc0007"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Grain</nobr> + Geometry</b> is designed as a set of loosely coupled algorithms and +class templates +united with a common idea, so that all the components can be easily +combined. +Also, the template based design allows you to replace any part of the +library without the +necessity to modify a single byte in the existing code.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Also + <b>AGG</b> is designed keeping in mind extensibility and flexibility. +Basically I just wanted +to create a toolkit that would allow me (and anyone else) to add new +fancy +algorithms very easily.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b>AGG</b> + does not dictate you any style of its use, you are free to use any part + +of it. However, <b>AGG</b> is often associated with a tool for rendering + images in memory. +That is not quite true, but it can be a good starting point in studying. + +The tutorials describe the use of <b>AGG</b> starting from the low level + functionality that +deals with frame buffers and pixels. +Then you will gradually understand how to abstract different parts +of the library and how to use them separately. Remember, the raster +picture +is often not the only thing you want to obtain, you will probably want +to +print your graphics with highest possible quality and in this case you +can +easily combine the “vectorial” part of the library with some API like +Windows GDI, +having a common external interface. +If that API can render multi-polygons with non-zero and even-odd filling + rules +it's all you need to incorporate <b>AGG</b> into your application. For +example, Windows +API PolyPolygon perfectly fits these needs, except certain advanced +things like +gradient filling, Gouraud shading, image transformations, and so on. Or, + as +an alternative, you can use all <b>AGG</b> algorithms producing high +resolution pixel +images and then to send the result to the printer as a pixel map.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Below + is a typical brief scheme of the <b>AGG</b> rendering pipeline. <br> +<a name="TYPICAL_SCHEME"><b></b></a><table align="left"><tbody><tr><td><center><img + src="introduction.agdoc_files/typical_scheme.gif" title="Typical Scheme + of the Rendering Pipeline" border="0"></center></td></tr><tr><td><i><center>Typical + Scheme of the Rendering Pipeline</center></i></td></tr></tbody></table> +<br> +Please note that any component between the “Vertex Source” and +“Screen Output” is not mandatory. It all depends on your particular +needs. For example, +you can use your own rasterizer, based on Windows API. In this case you +won't need +the AGG rasterizer and renderers. Or, if you need to draw only lines, +you can use the +AGG <b>outline</b> rasterizer that has certain restrictions but works +faster. The number of +possibilities is endless.</p></td></tr></tbody></table> + + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Here: +</p><ul type="disc"> +<li><b>Vertex Source</b> is some object that produces polygons or +polylines as + a set of consecutive 2D vertices with commands like “MoveTo”, +“LineTo”. + It can be a container or some other object that generates vertices on + demand.</li> +<li><b>Coordinate conversion pipeline</b> consists of a number of +coordinate converters. + It always works with vectorial data (X,Y) represented as floating +point numbers + <nobr>(double)</nobr>. For example, it can contain an affine +transformer, outline (stroke) + generator, some marker generator (like arrowheads/arrowtails), dashed + lines + generator, and so on. The pipeline can have branches and you also can + have any + number of different pipelines. You also can write your own converter +and include + it into the pipeline.</li> +<li><b>Scanline Rasterizer</b> converts vectorial data into a number of +horizontal scanlines. + The scanlines usually (but not obligatory) carry information about <b><nobr>Anti-Aliasing</nobr></b> + as + “coverage” values. </li> +<li><b>Renderers</b> render scanlines, sorry for the tautology. The +simplest example is + solid filling. The renderer just adds a color to the scanline and +writes the result + into the rendering buffer. More complex renderers can produce +multi-color result, + like gradients, Gouraud shading, image transformations, patterns, and + so on.</li> +<li><b>Rendering Buffer</b> is a buffer in memory that will be displayed + afterwards. Usually + but not obligatory it contains pixels in format that fits your video +system. For example, + 24 bits <nobr>B-G-R</nobr>, 32 bits <nobr>B-G-R-A</nobr>, or 15 bits <nobr>R-G-B-555</nobr> + for Windows. + But in general, there're no restrictions on pixel formats or color +space if + you write your own low level class that supports that format.</li></ul><p></p></td></tr></tbody></table> + + + +<h3>Colors, Color Spaces, and Pixel Formats<a name="toc0008"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Colors + in <b>AGG</b> appear only in renderers, that is, when you actually put +some data +to the rendering buffer. In general, there's no general purpose +structure or +class like <b>“color”</b>, instead, <b>AGG</b> always operates with +concrete color space. +There are plenty of color spaces in the world, like RGB, HSV, CMYK, +etc., and +all of them have certain restrictions. For example, the RGB color space +is just a +poor subset of colors that a human eye can recognize. If you look at the + +full <a href="http://www.efg2.com/Lab/Graphics/Colors/Chromaticity.htm"><img + src="introduction.agdoc_files/link.gif" border="0"><b>CIE Chromaticity +Diagram</b></a>, you will see that +the RGB triangle is just a little part of it. +</p></td></tr></tbody></table><a name="CIE_1931"><b></b></a><table +width="640px"><tbody><tr><td><center><img +src="introduction.agdoc_files/cie_1931.jpg" title="CIE Chromaticity +Diagram and the RGB Gamut" border="0"><br><i>CIE Chromaticity Diagram +and the RGB Gamut</i></center></td></tr></tbody></table> +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>In +other words there are plenty +of colors in the real world that cannot be reproduced with RGB, CMYK, +HSV, etc. +Any color space except the one existing in Nature is restrictive. +Thus, it was decided not to introduce such an object like <b>“color”</b> + in order +not to restrict the possibilities in advance. Instead, there are objects + that +operate with concrete color spaces. Currently there are agg::<a +href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba">rgba</a> + and agg::<a +href="http://www.antigrain.com/__code/include/agg_color_rgba.h.html#rgba8">rgba8</a> + +that operate with the most popular <b>RGB</b> color space (strictly +speaking there's +RGB plus Alpha). The RGB color space is used with different pixel +formats, like +<nobr>24-bit</nobr> RGB or <nobr>32-bit</nobr> RGBA with different order + of color components. +But the common property of all of them is that they are essentially RGB. +Although, <b>AGG</b> doesn't explicitly support any other color spaces, +there is at +least a potential possibility of adding them. It means that all class +and +function templates that depend on the <b>“color”</b> type are +parameterized with the +<b>“ColorT”</b> argument.</p></td></tr></tbody></table> + + + +<h3>Coordinate Units<a name="toc0009"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Basically, + <b>AGG</b> operates with coordinates of the output device. +On your screen there are pixels. But unlike many other libraries and +APIs +<b>AGG</b> initially supports <b>Subpixel Accuracy</b>. It means that +the coordinates are represented as +<b>doubles</b>, where fractional values actually take effect. +<b>AGG</b> doesn't have an embedded conversion mechanism from <u>world</u> + to <u>screen</u> +coordinates in order not to restrict your freedom. It's very important +where and when +you do that conversion, so, different applications can require different + approaches. +<b>AGG</b> just provides you a transformer of that kind, namely, +that can convert your own <u>view port</u> to the <u>device</u> one. And + it's your responsibility +to include it into the proper place of the pipeline. You can also write +your own +very simple class that will allow you to operate with millimeters, +inches, or any +other physical units.</p></td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>Internally, + the rasterizers use integer coordinates of the format +24.8 bits, that is, 24 bits for the integer part and 8 bits for the +fractional one. In other words, all the internal coordinates are +multiplied +by 256. If you intend to use <b>AGG</b> in some embedded system that has + inefficient +floating point processing, you still can use the rasterizers with their +integer +interfaces. Although, you won't be able to use the floating point +coordinate pipelines +in this case.</p></td></tr></tbody></table> + + + + +<h3>AGG Building and Coding Notes<a name="toc0010"></a></h3> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p><b><nobr>Anti-Grain</nobr> + Geometry</b> doesn't have any rich and automated environvents to build. + <b>AGG</b> mantra is +<b>“It just compiles and works”</b>. It doesn't have any installation +packages either. Maybe it's not very good from the point of view of +automated +configuring and making of applications (like it's commonly used on +Unix), +but all you need to do is just add <b>AGG</b> source files into your +distribution +package as if they were your files. +As a benefit of this approach, you won't have any problems +with configuration files and endless <b>#ifdef…#elif…#endif</b>. This is + +possible because <b>AGG</b> has absolute minimum of external +dependencies. For Unix +there are the simplest possible <b>Makefiles</b> to build the <b>.a</b> +library, for +Windows there's no library created at all. All the demo examples just +include +the necessary source files. This practice allows for more convenient +debugging +process; in fact, almost all the examples are actually used to implement + +and debug the algorithms. It also advantages stability of the library, +because all +the algorithms suffer very deep testing in the conditions near to +operational. +</p></td></tr></tbody></table><table class="note" width="640px"><tbody><tr><td><b>NOTE</b><br> +If you want to use <b>AGG</b> in Windows Visual C++ environment, please +note that +there's no <b>“stdafx.h”</b> file used. It's <a +href="http://www.microsoft.com/"><img +src="introduction.agdoc_files/link.gif" border="0"><b>Microsoft</b></a> +specific and not +a part of C/C++ standard libraries, but <a +href="http://www.microsoft.com/"><img +src="introduction.agdoc_files/link.gif" border="0"><b>Microsoft</b></a> +just enforces to use it. +To successfully use <b>AGG</b> in Visual C++ projects don't forget to +turn off the +<b>“Precompiled Headers”</b> option for all <b>AGG</b> source files. +Besides, if you +link <b>AGG</b> with static <b>MFC</b> you will probably have +duplicating <code>new</code> and <code>delete</code> +operators when linking. It's not because of <b>AGG</b>, it's because of <b>MFC</b>. +You will have the very same problem when you try to use any other <b>C++</b> +code that calls <code>new/delete</code> and doesn't include <b><nobr>stdafx.h</nobr></b>. +To resolve this situation follow the +<a +href="http://support.microsoft.com/default.aspx?scid=kb;en-us;q148652"><img + src="introduction.agdoc_files/link.gif" border="0"><b>Microsoft +recommendations</b></a> or just search in <a +href="http://www.google.com/"><img +src="introduction.agdoc_files/link.gif" border="0"><b>Google</b></a> for + <b>“<nobr>148652 LNK2005</nobr>”</b>. +</td></tr></tbody></table> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>As +it was mentioned above, <b>AGG</b> uses <b>C++</b> template mechanism +very actively. +However, it uses only well known and proven language constructions. A +good compatibility +is one of the primary aspirations. <b>C++</b> gurus can be suprised that + <b>AGG</b> doesn't use <b>STL</b>, +for example. It's done intentionally, in order not to have extra +dependencies +where the necessity of <b>STL</b> containers is very little. Of course, +it doesn't +prevent you from using <b>STL</b> or any other popular tools in a higher + level. +<b>AGG</b> is designed to have absolute minumum of potential conflicts +with existing <b>C++</b> +libraties, tools and technologies.</p></td></tr></tbody></table> + + + + +<br><h2>About this Manual<a name="toc0011"></a></h2> + +<table width="640px"><tbody><tr><td style="text-align: justify;"><p>As +it was said before <b>AGG</b> provides many different levels of +functionality, so +that you can use it in many different ways. For example, you may want to + use +<b>AGG</b> rasterizers without the scanline renderers. But for the sake +of +consistency and graduality we will start from the very beginning and +describe +all the functionality with examples. This approach might be slower than +some +“Quick Start”, but it will allow you to understand the conceps of the +design. +It is really useful because you will know how to replace certain classes + and +algorithms with your own, or how to extend the library. Particularly, +the +scanline renderers are platform independent, but not the fastest. You +may want +to write your own, optimized ones, but oriented to some hardware +archtecture, like SSE2.</p></td></tr></tbody></table> + +<br><table style="margin: 0px;" height="1px" width="640px" +bgcolor="#583927" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td></td></tr></tbody></table> +<table width="640px" border="0" cellpadding="0" cellspacing="0"> +<tbody><tr><td><center><span class="authors"> +Copyright <span class="larger">©</span> 2002-2006 +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +<tr><td><center><span class="authors"> +Web Design and Programming +<a href="http://www.antigrain.com/mcseem/index.html"><b>Maxim Shemanarev</b></a> +</span></center></td></tr> +</tbody></table> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br> +</body></html>
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