B.14 | Pictures and Colors

- The `picture` environment and the `graphics` Package
- The `color` Package

B.14.1 | The `picture` environment and the `graphics` Package

It is possible to have pictures and graphics processed by `imagen` (see section 6.1). In the case of the `picture` environment it remains users responsability to explicitly choose source chunks that will get rendered as GIF images. In the case of the commands from the `graphics` package, this choice is made by HEVEA. In both cases, the `imagen` script has to be run by hand. (However, note that HEVEA runs `imagen` when given the `-fix` command-line option.)
For instance consider the following picture:

    \newcounter{cms}
    \setlength{\unitlength}{1mm}
    \begin{picture}(50,10)
    \put(0,7){\makebox(0,0)[b]{cm}}
    \multiput(10,7)(10,0){5}{\addtocounter{cms}{1}\makebox(0,0)[b]{\arabic{cms}}}
    \multiput(1,0)(1,0){49}{\line(0,1){2.5}}
    \multiput(5,0)(10,0){5}{\line(0,1){5}}
    \thicklines
    \put(0,0){\line(1,0){50}}
    \multiput(0,0)(10,0){6}{\line(0,1){5}}
    \end{picture}

Users should enclose all picture elements in a `toimage` environment (or inside `%BEGIN IMAGE`... `%END IMAGE` comments) and insert an `\imageflush` command, where they want the image to appear in HTML output:

    %BEGIN IMAGE
    \newcounter{cms}
    \setlength{\unitlength}{1mm}
    \begin{picture}(50,10)
      ...
    \end{picture}
    %END IMAGE
    %HEVEA\imageflush

This will result in normal processing by LATEX and image inclusion by HEVEA:
All commands from the graphics package are implemented using the automatic image inclusion feature. More precisely, the outermost invocations of the `\includegraphics`, `\scalebox`, etc. commands are sent to the image image file and there will be one GIF image per outermost invocation of these commands.
For instance, consider a document `doc.tex` that loads the `graphics` package and that includes some (scaled) images by:

    \begin{center}
    \scalebox{.5}{\includegraphics{round.ps}}
    \scalebox{.75}{\includegraphics{round.ps}}
    \includegraphics{round.ps}
    \end{center}

Then, issuing the following two commands:

    # hevea doc.tex
    # imagen doc

yields HTML that basically consists in three image links, the images being generated by `imagen`.

B.14.2 | The `color` Package

HEVEA partly implements the `color` package. Implemented commands are `\definecolor`, `\color` and `\textcolor`. Other commands from the `color` package do not exist. At startup, colors `black`, `white`, `red`, `green`, `blue`, `cyan`, `yellow` and `magenta` are pre-defined.
Colors are defined by `\definecolor{`name`}{`model`}{`spec`}`, where name is the color name, model is the color model used, and spec is the color specification according to the given model. Defined colors are used by the declaration `\color{`name`}` and by the command `\textcolor{`name`}{`text`}`, which change text color. Please note that, the `\color` declaration accepts color specifications directly when invoked as `\color[`model`]{`spec`}`. The `\textcolor` command has a similar feature.
As regards color models, HEVEA implements the `rgb`, `cmyk`, `hsv` and `hls` color models. In those models, color specifications are floating point numbers less than one. For instance, here is the definition for the `red` color:

    \definecolor{red}{rgb}{1, 0, 0}

The `named` color model is also supported, in this model color specification are just names... Named colors are the ones of `dvips`.
GreenYellow, Yellow, Goldenrod, Dandelion, Apricot, Peach, Melon, YellowOrange, Orange, BurntOrange, Bittersweet, RedOrange, Mahogany, Maroon, BrickRed, Red, OrangeRed, RubineRed, WildStrawberry, Salmon, CarnationPink, Magenta, VioletRed, Rhodamine, Mulberry, RedViolet, Fuchsia, Lavender, Thistle, Orchid, DarkOrchid, Purple, Plum, Violet, RoyalPurple, BlueViolet, Periwinkle, CadetBlue, CornflowerBlue, MidnightBlue, NavyBlue, RoyalBlue, Blue, Cerulean, Cyan, ProcessBlue, SkyBlue, Turquoise, TealBlue, Aquamarine, BlueGreen, Emerald, JungleGreen, SeaGreen, Green, ForestGreen, PineGreen, LimeGreen, YellowGreen, SpringGreen, OliveGreen, RawSienna, Sepia, Brown, Tan, Gray, Black, White.
There are at least three ways to use colors from the `named` model.

1. Define a color name for them.
2. Specify the named color model as an optional argument to `\color` and `\textcolor`.
3. Use the names directly (HEVEA implements the `color` package with the `usenames` option given).

That is:

1. `\definecolor{rouge-brique}{named}{BrickRed}\textcolor{rouge-brique}{Text as a brick}`.
2. `\textcolor[named]{BrickRed}{Text as another brick}`.
3. `\textcolor{BrickRed}{Text as another brick}`.

Which yields:

1. Text as a brick.
2. Text as another brick.
3. Text as another brick.

Colors should be used carefully. Too many colors hinders clarity and some of the colors may not be readable on the document background color.

B.14.2.1 | The `bgcolor` environment

Due to limitations in HTML 3.2 (and 4.0 transitional viewed as 3.2!), it is not possible to implement the `\colorbox` command for changing the background color inside a paragraph.
However, HEVEA features a `bgcolor` environment, for changing the backgroud color of some subparts of the document. The `bgcolor` environment is a displayed environment and it normally starts a new line. Simple usage is `\begin{bgcolor}{`color`}`... `\end{bgcolor}`, where color is a color defined with `\definecolor`. Hence the following source yield a paragraph with a red background:

    \begin{bgcolor}{red}
    \color{yellow}Yellow letters on a red backgroud
    \end{bgcolor}

Yellow letters on a red backgroud

The `bgcolor` environment is implemented by a `TABLE` element, it takes an optional argument that is used as an attribute for this `TABLE` element (default value is `CELLPADDING=10`). For instance, the following source:

    \begin{bgcolor}[CELLPADDING=0]{yellow}
    \color{red}Red letters on a yellow backgroud
    \end{bgcolor}

will be typeset on a yellow background and without padding:

Red letters on a yellow backgroud

B.14.2.2 | From High-Level Colors to Low-Level Colors

High-level colors are color names defined with `\definecolor`. Low-level colors are HTML-style colors. That is, they are either one of the sixteen conventional colors black, silver etc., or a RGB hexadecimal color specification of the form `"#XXXXXX"`.
One changes the high-level high-color into a low-level color by `\@getcolor{`high-color`}`. Low-level colors are appropriate inside HTML attributes and as arguments to the `\@fontcolor` internal macro. An example of `\@getcolor` usage can be found at the end of section 8.5.