Add support for \matrix

* Add matrix parsing

Matrices are parsed into a `matrix` struct that contains the matrix rows.
Tests ensure that simple and more complex matrices are being parsed correctly
as well as triggering the potential "missing closing brace error".

* Add initial version of matrix noad layouting

* Initial working version of arbitrarily sized assembled delimiters

* Tidy up

* Fit and finish for arbitrarily sized delimiters and matrices

* Add assembled delimiters and matrices to docs

* Fix unit tests

* Additional unit tests

* Add new approval test approved files

* Finalize tests and update approval files - Correct algorithm for determining best auto sized glyph

* 🎨 Committing clang-format changes

---------

Co-authored-by: Clang Robot <robot@example.com>

Author: cpp-niel

doc/features.md

@@ -14,6 +14,7 @@ of approval tests used to help test the library for regressions.
 - [Subscripts and Superscripts](#subscripts-and-superscripts)
 - [Fractions](#fractions)
 - [Radicals](#radicals)
+- [Matrices](#matrices)
 - [Big Operators](#big-operators)
 - [Accents](#accents)
 - [Overlining and Underlining](#overlining-and-underlining)
@@ -29,36 +30,49 @@ of approval tests used to help test the library for regressions.
     - [Punctuation](#punctuation)
     - [Others](#others)
 - [Spaces](#spaces)
-    
 
 ## Subscripts and Superscripts
 
 Subscripts and superscripts including all levels of nesting are supported:
 
 ![](./../tests/approval_tests/approved_files/docs.subscripts_and_superscripts.approved.svg)
 
-
 ## Fractions
 
 There is full support for the standard `\frac` command - again, including all levels of nesting:
 
 ![](./../tests/approval_tests/approved_files/docs.fractions.approved.svg)
 
-The `\binom` command is also supported and anything that is not covered by either `\frac` or 
+The `\binom` command is also supported and anything that is not covered by either `\frac` or
 `\binom` can be achieved using the generalized fraction command `\genfrac`:
 
 ![](./../tests/approval_tests/approved_files/docs.genfrac.approved.svg)
 
-Note that in generalized fractions the third argument - the line thickness - is always in points and that currently 
+Note that in generalized fractions the third argument - the line thickness - is always in points and that currently
 the fourth argument - the style - is ignored and treated as if `\displaystyle` was set.
 
-
 ## Radicals
 
 *mfl* has full support for radicals, including the optional degree and unlimited nesting:
 
 ![](./../tests/approval_tests/approved_files/docs.radicals.approved.svg)
 
+## Matrices
+
+TeX-style matrices are supported via the `\matrix` command:
+
+![](./../tests/approval_tests/approved_files/docs.matrix.approved.svg)
+
+For example, *J* in the second row above is defined as follows:
+
+```
+J = \left(\matrix{
+        \frac{\partial f_1}{\partial x_1} & \frac{\partial f_1}{\partial x_2} & \cdots & \frac{\partial f_1}{\partial x_n} \cr
+        \frac{\partial f_2}{\partial x_1} & \frac{\partial f_2}{\partial x_2} & \cdots & \frac{\partial f_2}{\partial x_n} \cr
+        \vdots                            & \vdots                            & \ddots & \vdots                            \cr
+        \frac{\partial f_m}{\partial x_1} & \frac{\partial f_m}{\partial x_2} & \cdots & \frac{\partial f_m}{\partial x_n}
+    }\right)
+```
 
 ## Big Operators
 
@@ -75,7 +89,6 @@ The extended integral symbols are also considered big operators:
 
 ![](./../tests/approval_tests/approved_files/docs.big_ops_integrals.approved.svg)
 
-
 ## Accents
 
 There is support for the common mathematical accents:
@@ -90,14 +103,12 @@ There is also support for some additional mathematical accents:
 
 ![](./../tests/approval_tests/approved_files/docs.additional_accents.approved.svg)
 
-
 ## Overlining and Underlining
 
 The automatic positioning and sizing of overlines and underlines is fully supported:
 
 ![](./../tests/approval_tests/approved_files/docs.lines.approved.svg)
 
-
 ## Functions and User Defined Operators
 
 Unlike variables, known functions are typeset in roman instead of italics. *mfl* also
@@ -110,7 +121,6 @@ behave like built-in functions:
 
 ![](./../tests/approval_tests/approved_files/docs.operatorname.approved.svg)
 
-
 ## Delimiters
 
 The following symbols are recognized as opening and closing delimiters:
@@ -122,17 +132,20 @@ available, and the dot variants `\left.` and `\right.` can be used to omit one o
 
 ![](./../tests/approval_tests/approved_files/docs.sized_delimiters.approved.svg)
 
+If supported by the font, *mfl* will also assemble delimiters from "parts" allowing the use of
+oversized - and effectively arbitrarily sized - delimiters:
+
+![](./../tests/approval_tests/approved_files/docs.extra_large_delimiters.approved.svg)
 
 ## Fonts
 
 *mfl* only supports the scoped font switches (like `\mathrm`, `\mathit` etc.) and not the
 deprecated state switches (like `\rm`, `\it` etc.). *mfl* recognises the font
-commands in the examples below. Availability and appearance of glyphs will of course 
+commands in the examples below. Availability and appearance of glyphs will of course
 depend on the actual fonts that are being used. This is what the *Stix2* fonts look like:
 
 ![](./../tests/approval_tests/approved_files/docs.fonts.approved.svg)
 
-
 ## Symbols
 
 *mfl* recognises most mathematical symbols. Here is an overview of the most important ones
@@ -142,12 +155,11 @@ for reference.
 
 ![](./../tests/approval_tests/approved_files/docs.greek_alphabet_lowercase.approved.svg)
 
-As per mathematical convention, Greek capitals are automatically set in roman font and 
+As per mathematical convention, Greek capitals are automatically set in roman font and
 not in italics.
 
 ![](./../tests/approval_tests/approved_files/docs.greek_alphabet_uppercase.approved.svg)
 
-
 ### Binary Operators
 
 *mfl* supports the basic TeX binary operators:
@@ -158,7 +170,6 @@ as well as various binary operators from additional packages like the AMS packag
 
 ![](./../tests/approval_tests/approved_files/docs.additional_binary_operators.approved.svg)
 
-
 ### Relational Operators
 
 Similarly to the binary operators, *mfl* supports the fundamental relational operators:
@@ -169,7 +180,6 @@ but also recognises many others:
 
 ![](./../tests/approval_tests/approved_files/docs.additional_relational_operators.approved.svg)
 
-
 #### Negations
 
 Many relations can be negated by prepending `\not`:
@@ -180,7 +190,6 @@ and some further negated relational operators are also supported:
 
 ![](./../tests/approval_tests/approved_files/docs.additional_negations.approved.svg)
 
-
 ### Arrows
 
 The TeX arrow symbols are supported:
@@ -191,14 +200,12 @@ and *mfl* will also recognise the following extended set of arrow symbols:
 
 ![](./../tests/approval_tests/approved_files/docs.additional_arrows.approved.svg)
 
-
 ### Punctuation
 
 *mfl* recognises the following symbols as punctuation:
 
 ![](./../tests/approval_tests/approved_files/docs.punctuation.approved.svg)
 
-
 ### Others
 
 For completeness, the following tables show the remaining supported symbols:
@@ -207,7 +214,6 @@ For completeness, the following tables show the remaining supported symbols:
 ![](./../tests/approval_tests/approved_files/docs.combining_symbols.approved.svg)
 ![](./../tests/approval_tests/approved_files/docs.dots.approved.svg)
 
-
 ## Spaces
 
 The following mathematical spacing commands are recognized by *mfl*:

include/mfl/abstract_font_face.hpp

@@ -4,10 +4,9 @@
 #include "mfl/font_family.hpp"
 #include "mfl/units.hpp"
 
-#include <cstddef>
-#include <cstdint>
 #include <functional>
 #include <memory>
+#include <optional>
 #include <vector>
 
 namespace mfl
@@ -68,6 +67,21 @@ namespace mfl
         std::int32_t size = 0;
     };
 
+    struct glyph_part
+    {
+        size_t glyph_index = 0;
+        std::int32_t start_connector_length = 0;
+        std::int32_t end_connector_length = 0;
+        std::int32_t full_advance = 0;
+        bool is_extender;
+    };
+
+    struct glyph_assembly
+    {
+        std::vector<glyph_part> parts;
+        std::int32_t italic_correction;
+    };
+
     struct abstract_font_face
     {
         virtual ~abstract_font_face() = default;
@@ -77,6 +91,8 @@ namespace mfl
                                                                  const bool use_large_variant) const = 0;
         [[nodiscard]] virtual std::vector<size_variant> horizontal_size_variants(const code_point char_code) const = 0;
         [[nodiscard]] virtual std::vector<size_variant> vertical_size_variants(const code_point char_code) const = 0;
+        [[nodiscard]] virtual std::optional<glyph_assembly> horizontal_assembly(const code_point char_code) const = 0;
+        [[nodiscard]] virtual std::optional<glyph_assembly> vertical_assembly(const code_point char_code) const = 0;
         virtual void set_size(const points size) = 0;
     };
 

include/mfl/detail/quantity.hpp

@@ -85,5 +85,7 @@ namespace mfl::detail
 
     template <typename Tag>
     std::ostream& operator<<(std::ostream& os, const quantity<Tag>& p)
-    { return os << std::format("{}", p); }
+    {
+        return os << std::format("{}", p);
+    }
 }

include/mfl/units.hpp

@@ -23,7 +23,9 @@ namespace mfl
 
         constexpr dots_per_inch operator""_dpi(const long double x) { return dots_per_inch{static_cast<double>(x)}; }
         constexpr dots_per_inch operator""_dpi(const unsigned long long x)
-        { return dots_per_inch{static_cast<double>(x)}; }
+        {
+            return dots_per_inch{static_cast<double>(x)};
+        }
 
         constexpr pixels operator""_px(const long double x) { return pixels{static_cast<double>(x)}; }
         constexpr pixels operator""_px(const unsigned long long x) { return pixels{static_cast<double>(x)}; }

src/CMakeLists.txt

@@ -11,6 +11,7 @@ add_library(mfl
         noad/gen_script.cpp
         noad/left_right.cpp
         noad/math_char.cpp
+        noad/matrix.cpp
         noad/noad.cpp
         noad/overline.cpp
         noad/radical.cpp
@@ -33,6 +34,7 @@ add_library(mfl
         parser/line.cpp
         parser/math_char.cpp
         parser/math_space.cpp
+        parser/matrix.cpp
         parser/parse.cpp
         parser/parser_state.cpp
         parser/parser_utilities.cpp