ipe2tikz

This is a TikZ exporter ipelet: a plugin for Ipe that exports readable TikZ pictures for use in LaTeX documents.

yields

\begin{tikzpicture}[ipe import]
  \draw[red, thick]
    (16, 48) rectangle (48, 16);
  \filldraw[fill=blue, semitransparent]
    (32, 32) circle[radius=16];
\end{tikzpicture}

TikZ is an amazing piece of software. To sketch a complicated shape, though, you really want a GUI, like Ipe. This ipelet is meant to allow you to sketch something in Ipe, then export it into readable TikZ code that you can tweak and perhaps use in a larger picture. It is also quite good at exporting large and complex Ipe files (subject to the limitations below) into standalone LaTeX documents. Thankfully, Ipe is well-suited to generating readable TikZ code, since they both rely on flexible symbolic style mechanisms to specify most drawing parameters.

Installation

1. Copy tikz.isy into ~/.ipe/styles on Linux and Macs. On Windows, I believe you have to use the directory containing the built-in stylesheets.
2. Copy tikz.lua into ~/.ipe/ipelets on Linux and Macs, and into $USERPROFILE\Ipelets on Windows.
3. Copy tikzlibraryipe.code.tex somewhere LaTeX can find it, e.g. the same directory as the LaTeX file you're trying to compile.

I have only tested this with Ipe versions 7.2.?, on Linux and Macs. You can file a bug report if it doesn't work on your system or Ipe version, but I probably won't know how to fix it unless you include a patch or pull request.

Usage

This ipelet supports exporting the current view to a TeX file, or replacing the selected objects by a text box containing TikZ code that reproduces those objects.

Before you start, you should choose whether you want to primarily use TikZ's styles or Ipe's styles.

Using TikZ's styles

Use TikZ's styles if you want to make a sketch in Ipe, but do most of the work in TikZ. In this case, you want Ipe's styles to reflect TikZ's styles as closely as possible: for instance, the pen widths should be very thin, thin, thick, etc., arrows should include Computer Modern Rightarrow and Stealth, and so on. To do this, use tikz.isy instead of the basic.isy stylesheet, and un-check Export stylesheet in the ipelet dialog. Be sure to include the TikZ libraries arrows.meta and patterns, and the provided library ipe (i.e. tikzlibraryipe.code.tex) in your LaTeX code. The latter defines a style ipe import, which should be executed in any tikzpicture (or scope) using exported Ipe code.

In this mode, all Ipe symbols you use must already be known to TikZ as keys.

Using Ipe's styles

Use Ipe's styles if (a) you are more comfortable with Ipe's styles than TikZ's, and (b) you want to do most of the drawing in Ipe, then tweak it in TikZ afterwards. To do this, check Export stylesheet in the ipelet dialog. This mode has the additional effect of adding an ipe ... prefix to many style names: for instance, the heavier pen becomes ipe pen heavier in TikZ. This means that, if you have an Ipe pen width named thick, it will be exported to ipe pen thick, and all thick paths will reference ipe pen thick. This is probably what you want to happen, but it does mean that you can't make a path that uses TikZ's native thick style when Export Stylesheets is checked.

The stylesheet cascade is exported into a TikZ style called ipe stylesheet. Among other things, this style contains:

• The ipe import key.
• Settings for the fill rule, line join, and line cap.
• Settings for the pen width, dash styles, and opacity styles.
• Settings to alias the > arrow tip to Ipe's normal arrow.

The style does not contain settings for marks, arrows, tilings, and some others: see limitations below.

Exporting to a file

In this mode, the ipelet creates a file with the TikZ code necessary to reproduce the current view on the current page. This is suitable for \inputting or copying into a LaTeX document.

Select Export to File from the TikZ Export submenu in the ipelets menu, or use the shortcut Alt+T. A dialog appears, with the following options:

• Export complete document: if this is checked, the ipelet makes a document that can be compiled standalone. That is, it generates a preamble, \begin{document}...\end{document} tags, etc. If you want to \input the output file into another LaTeX file, un-check this option. In that case, be sure to set \usetikzlibrary{arrows.meta,patterns,ipe} somewhere.
• Export stylesheet: if this is checked, the ipelet makes a TikZ version of the effective styles as determined by the Ipe stylesheet cascade (see above), except for colors.
• Export colors: if this is checked, the ipelet generates \definecolor commands for all colors defined in your Ipe stylesheets.
• Export scope instead of tikzpicture: if this is checked, the generator puts TikZ code inside a scope environment instead of a tikzpicture environment. Such a file is suitable for \inputting directly into a tikzpicture environment, as a subpicture. (To apply additional transformations, enclose the \input in another scope.) This option is disabled if Export complete document is checked.
• Export grid: if desired, you can export Ipe's grid as well. This is useful for debugging the placement of objects.
• Output file: this is where the TikZ code goes.

If Export complete document is unchecked and a coordinate system is defined, the origin of the coordinate system becomes TikZ's origin.

Exporting to a text box

In this mode, the user selects some number of objects, and the ipelet replaces them by a text box containing TikZ code to reproduce those objects. This is useful for the following kind of workflow:

1. Create a quick picture in Ipe.
2. Convert it in-place to TikZ.
3. Edit the TikZ code in the Ipe textbox, and use the Apply button to immediately see your changes while editing.
4. Copy-paste the resulting TikZ picture to a LaTeX document.

For this to work, you must have Ipe 7.2.6+ installed, and you need to put tikzlibraryipe.code.tex either in ~/.ipe/latexrun, or somewhere in your $TEXINPUTS path. (I don't know where these are on Windows.)

To use, first select the objects you want to convert to TikZ. Select Export to Text Object from the TikZ Export submenu in the ipelets menu, or use the shortcut Ctrl+Shift+T. A dialog appears, with one option:

• Use TikZ styles: this is the opposite of the Export stylesheet option in the file export dialog. If unchecked, the ipelet will produce a TikZ style for Ipe's current styles. All TikZ pictures created using Export to Text Object must use the same setting for this option.

After clicking Ok, the following things happen:

1. The ipelet creates an invisible layer called _TikZ replaced, and moves the selected objects to that layer.
2. The ipelet creates a style sheet called TikZ-export, which contains the necessary preamble material to compile the TikZ code in the text box. This includes the TikZ style, if Use TikZ styles is not checked.
3. The ipelet creates a text box and populates it with the generated TikZ code. The position (reference point) of the text box is TikZ's origin. By default, the position of the text box is the lower-left corner of the bounding box of the selected objects, but if you have defined a coordinate system, the ipelet will use the origin of the coordinate system instead.

What it Does

The best way to get a feel for what the exporter does is to doodle in Ipe and see what TikZ code is produced. The ipelet code also has a lot of comments, if you want to dig for details. In summary:

• Path objects are exported to usual TikZ paths, created with \draw or \fill or \filldraw. These may contain path-to -- commands, arc commands, and curve-to .. commands, as well as rectangle, ellipse, and circle commands. Composed paths are concatenated by move-to (empty) commands.
• Text objects are exported to TikZ nodes, with the ipe node style.
• Group objects are exported to TikZ scopes. The clipping path, if it exists, becomes a \clip path in the scope.
• Reference objects (marks) are exported to TikZ \pic commands.
• If configured to do so, the stylesheet cascade is exported to a TikZ style called ipe stylesheet.

Coordinate transformations

Objects in Ipe may have coordinate transformations applied to them. In order to produce readable TikZ code, these are handled as follows.

• If the transformation is just a translation, it is absorbed into any path coordinates. This is the only reasonable thing to do, since any time you translate an object in Ipe, you are actually updating the transformation matrix.
• For path, group, and text objects, if the transformation has a nontrivial linear part, then try to decompose it as a rotation and a scale. If that works, add rotate= and scale= options to the path. (Marks only have translations in their coordinate transformations.)
• If the decomposition didn't work, use TikZ's cm= option to pass the coordinate matrix directly.
• In either of the above two cases, it's not always clear what point to use as the origin in the transformation: in Ipe, this is the origin of the paper at the time the object was created, which doesn't make much sense in code meant to be read by humans. For path objects, the ipelet uses the first mentioned coordinate as the origin. For group objects, I don't see any better origin to use: rotating and scaling group objects will produce somewhat funny-looking code, unless you are careful to create the group object near the origin. Text objects have a well-defined "position", so that is used as the origin.

Styles and options

Most options are exported symbolically, hopefully in the way one would expect. Some are exported as numbers or RGB triples, if necessary. If not using Export stylesheet, then all exported symbols must already be known to TikZ as keys.

The TikZ stylesheet tikz.isy

This file teaches Ipe to use TikZ's styles for almost everything it can draw. Among other things, this file contains:

• Color definitions for the built-in colors from xcolor.
• The TikZ default line cap, join, and fill rules.
• TikZ's pen widths, dash styles, and opacity styles.
• Some of TikZ's built-in fill patterns, used for tilings.
• Definitions of Ipe's standard mark/reference shapes. (TikZ has no analogue to use instead.)
• Definitions of some of TikZ's standard arrows, so Ipe knows how to draw them. Since TikZ's arrow facility is much more sophisticated than Ipe's, exported TikZ arrows will not look quite the same as they did in Ipe.
• Ipe's usual textsize definitions.

The Ipe compatibility library tikzlibraryipe.code.tex

This file is the TikZ glue that complements the ipelet. This file essentially consists of the ipe import style, which contains (among other things):

• The definitions x=1bp and y=1bp. The basic unit in Ipe is the PDF point (1/72 of an inch), which in LaTeX is a "big point" (as opposed to a "Knuth point", which is slightly smaller). If the exported code is to be readable, it had better use Ipe's basic unit.
• The definition of the ipe node style, which sets the default anchor and scale factor, and removes inner and outer separation.
• Arrow tip definitions for Ipe's arrows. Ipe's arrows already look like certain standard TikZ arrows (Stealth, Triangle, etc.), but they behave rather differently with respect to line width, tip position, join style, etc. The arrows defined in the ipe library behave almost exactly like Ipe's arrows.
• Definitions of Ipe's marks (circle, disk, etc.) as TikZ pic commands.

Limitations

• Exporting gradients and effects is not supported. Gradients could in theory be exported as shades, if someone wanted to code it. Effects probably cannot be implemented within PGF/TikZ.
• Exporting bitmapped images is not supported. You can use \includegraphics within a text object in Ipe, after putting \usepackage{graphicx} in the preamble. The image will display in Ipe (if you have a recent enough version), and it should appear after compiling the exported code.
• Only the current page, and the current view on that page, are exported.
• The ipelet won't export symbols (marks and arrows) from stylesheets; these have to be defined by hand in a TikZ style. Note however that Ipe's standard marks and arrows are already defined in tikzlibraryipe.code.tex.
• The ipelet won't export tilings / fill patterns from stylesheets either; these must also be done by hand. It requires a bit of work to define a new fill pattern in TikZ. For this reason, only the fill patterns that are predefined in TikZ and which can also be drawn by Ipe are defined in tikz.isy.
• When in Export complete document mode, the size of the paper in LaTeX is set to the size of the paper in Ipe. However, Ipe also sets PDF's ArtBox and (optionally) CropBox to the bounding box of the image. The ipelet does not do that, as TikZ/PGF has no such facility, these being PDF-specific features. The result is that your PDF reader may display a PDF saved directly from Ipe on a smaller canvas than when it is exported through TikZ first.
• Some colors may look different after compiling LaTeX unless you put \PassOptionsToPackage{rgb}{xcolor} before \documentclass in your LaTeX file. (This happens, for instance, when using symbolic colors defined by xcolor in cmyk, and defined in tikz.isy or another stylesheet in rgb.)
• TikZ's math is done by TeX, so it suffers from some inaccuracy, and all numbers have to be kept rather small. Crazy coordinate transformations may push the limits of what it can do.