Merge pull request matplotlib#7291 from rougier/MEP29

MEP 29: Markup text

Author: efiring

doc/devel/MEP/MEP29.rst

@@ -0,0 +1,82 @@
+=========================
+ MEP29: Text light markup
+=========================
+
+.. contents::
+   :local:
+
+
+Status
+======
+
+Discussion
+
+
+Branches and Pull requests
+==========================
+
+None at the moment, proof of concept only.
+
+Abstract
+========
+
+This MEP proposes to add lightweight markup to the text artist.
+
+Detailed description
+====================
+
+Using different size/color/family in a text annotation is difficult because the
+`text` method accepts argument for size/color/family/weight/etc. that are used
+for the whole text. But, if one wants, for example, to have different colors,
+one has to look at the gallery where one such example is provided:
+http://matplotlib.org/examples/text_labels_and_annotations/rainbow_text.html
+
+This example takes a list of strings as well as a list of colors which makes it
+cumbersome to use. An alternative would be to use a restricted set of pango-like markup (see https://developer.gnome.org/pango/stable/PangoMarkupFormat.html) and to interpret this markup.
+
+Some markup examples::
+
+   Hello <b>world!</b>`
+   Hello <span color="blue">world!</span>
+
+
+Implementation
+==============
+
+A proof of concept is provided in `markup_example.py <https://github.com/rougier/matplotlib/blob/markup/examples/text_labels_and_annotations/markup.py>`_ but it currently only handles the horizontal direction.
+
+Improvements
+------------
+
+* This proof of concept uses regex to parse the text but it may be better
+  to use the html.parser from the standard library.
+
+* Computation of text fragment positions could benefit from the OffsetFrom
+  class. See for example item 5 in `Using Complex Coordinates with Annotations <http://matplotlib.org/devdocs/users/annotations.html#using-complex-coordinates-with-annotations>`_
+
+Problems
+--------
+
+* One serious problem is how to deal with text having both latex and
+  html-like tags. For example, consider the follwing::
+
+     $<b>Bold$</b>
+
+  Recommendation would be to have mutual exclusion.
+
+
+Backward compatibility
+======================
+
+None at the moment since it is only a proof of concept
+
+
+Alternatives
+============
+
+As proposed by @anntzer, this could be also implemented as improvements to
+mathtext. For example::
+
+  r"$\text{Hello \textbf{world}}$"
+  r"$\text{Hello \textcolor{blue}{world}}$"
+  r"$\text{Hello \textsf{\small world}}$"

doc/devel/MEP/index.rst

@@ -30,3 +30,5 @@ Matplotlib Enhancement Proposals
    MEP26
    MEP27
    MEP28
+   MEP29
+