Merge pull request #2174 from Omikhleia/fix-math-primes-asterisk

Fix math primes and asterisk
sile-typesetter · Nov 23, 2024 · 6bc618c · 6bc618c
2 parents f324a15 + b2ca8b4
commit 6bc618c
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Showing 17 changed files with 705 additions and 181 deletions.
diff --git a/packages/math/base-elements.lua b/packages/math/base-elements.lua
@@ -947,6 +947,17 @@ end
 
 function elements.text:shape ()
    self.font.size = self.font.size * self:getScaleDown()
+   if isScriptMode(self.mode) then
+      local scriptFeature = SILE.settings:get("math.font.script.feature")
+      if scriptFeature then
+         self.font.features = ("+%s=1"):format(scriptFeature)
+      end
+   elseif isScriptScriptMode(self.mode) then
+      local scriptFeature = SILE.settings:get("math.font.script.feature")
+      if scriptFeature then
+         self.font.features = ("+%s=2"):format(scriptFeature)
+      end
+   end
    local face = SILE.font.cache(self.font, SILE.shaper.getFace)
    local mathMetrics = self:getMathMetrics()
    local glyphs = SILE.shaper:shapeToken(self.text, self.font)

diff --git a/packages/math/init.lua b/packages/math/init.lua
@@ -35,6 +35,12 @@ function package.declareSettings (_)
       type = "integer",
       default = 400,
    })
+   SILE.settings:declare({
+      parameter = "math.font.script.feature",
+      type = "string or nil",
+      default = "ssty",
+      help = "OpenType feature for the math script-style alternates (esp. primes), theoretically ssty",
+   })
    SILE.settings:declare({
       parameter = "math.font.filename",
       type = "string",
@@ -138,6 +144,10 @@ By default, this package uses Libertinus Math, so it will fail if Libertinus Mat
 Another font may be specified via the setting \autodoc:setting{math.font.family}.
 If required, you can set the font style and weight via \autodoc:setting{math.font.style} and \autodoc:setting{math.font.weight}.
 The font size can be set via \autodoc:setting{math.font.size}.
+The \autodoc:setting{math.font.script.feature} setting can be used to specify OpenType features for the math font, which are applied to the smaller script styles.
+It defaults to \code{ssty} (script style alternates), notably to ensure that some symbols such as the prime, double prime, etc. are displayed correctly.
+The default setting applies to Libertinus Math and well-designed math fonts, but some fonts may require different features.
+(The STIX Two Math font has a stylitic set \code{ss04} from primes only, but also supports, according to its documentation, \code{ssty}, which provides other optical adjustments.)
 
 \paragraph{MathML}
 The first way to typeset math formulas is to enter them in the MathML format.

diff --git a/packages/math/texlike.lua b/packages/math/texlike.lua
@@ -107,16 +107,49 @@ local mathGrammar = function (_ENV)
          return pl.utils.unpack(t)
          end
 
+   -- TeX uses the regular asterisk (* = U+002A) in superscripts or subscript:
+   -- The TeXbook exercice 18.32 (p. 179, 330) for instance.
+   -- Fonts usually have the asterisk raised too high, so using the Unicode
+   -- asterisk operator U+2217 looks better (= \ast in TeX).
+   local astop = P"*" / luautf8.char(0x2217)
+   -- TeX interprets apostrophes as primes in math mode:
+   -- The TeXbook p. 130 expands ' to ^\prime commands and repeats the \prime
+   -- for multiple apostrophes.
+   -- The TeXbook p. 134: "Then there is the character ', which we know is used
+   -- as an abbreviation for \prime superscripts."
+   -- (So we are really sure superscript primes are really the intended meaning.)
+   -- Here we use the Unicode characters for primes, but the intent is the same.
+   local primes = (
+         P"''''" / luautf8.char(0x2057) + -- quadruple prime
+         P"'''" / luautf8.char(0x2034) + -- triple prime
+         P"''" / luautf8.char(0x2033) + -- double prime
+         P"'" / luautf8.char(0x2032) -- prime
+      ) / function (s)
+            return { id="atom", s }
+         end
+   local primes_sup = (
+         primes * _ * P"^" * _ * element_no_infix / function (p, e)
+            -- Combine the prime with the superscript in the same mathlist
+            if e.id == "mathlist" then
+               table.insert(e, 1, p)
+               return e
+            end
+            return { id="mathlist", p, e }
+         end
+         + primes -- or standalone primes
+      )
+
    START "math"
    math = V"mathlist" * EOF"Unexpected character at end of math code"
    mathlist = (comment + (WS * _) + element)^0
-   supsub = element_no_infix * _ * P"^" * _ * element_no_infix * _ *
-      P"_" * _ * element_no_infix
-   subsup = element_no_infix * _ * P"_" * _ * element_no_infix * _ *
-      P"^" * _ * element_no_infix
-   sup = element_no_infix * _ * P"^" * _ * element_no_infix
+   supsub = element_no_infix * _ * primes_sup                  * _ *  P"_" * _ * element_no_infix +
+            element_no_infix * _ * P"^" * _ * element_no_infix * _ *  P"_" * _ * element_no_infix
+   subsup = element_no_infix * _ * P"_" * _ * element_no_infix * primes_sup +
+            element_no_infix * _ * P"_" * _ * element_no_infix * _ * P"^" * _ * element_no_infix
+   sup =  element_no_infix * _ * primes_sup +
+          element_no_infix * _ * P"^" * _ * element_no_infix
    sub = element_no_infix * _ * P"_" * _ * element_no_infix
-   atom = natural + C(utf8code - S"\\{}%^_&") +
+   atom = natural + astop + C(utf8code - S"\\{}%^_&'") +
       (P"\\{" + P"\\}") / function (s) return string.sub(s, -1) end
    text = (
          P"\\text" *

diff --git a/tests/bug-1495-inline-math-layout.expected b/tests/bug-1495-inline-math-layout.expected
@@ -54,7 +54,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	196.6642
 My 	37.4447
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	198.4962
 T	3421 w=4.5776	(nil)
@@ -101,7 +101,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	199.7501
 My 	49.5701
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	201.5821
 T	3413 w=3.5152	(nil)

diff --git a/tests/feat-math-display-numbered.expected b/tests/feat-math-display-numbered.expected
@@ -12,7 +12,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	129.6547
 My 	48.7418
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	131.4867
 T	3421 w=4.5776	(nil)
@@ -49,7 +49,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	129.6547
 My 	108.3223
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	131.4867
 T	3421 w=4.5776	(nil)
@@ -88,7 +88,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	129.6547
 My 	167.9027
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	131.4867
 T	3421 w=4.5776	(nil)
@@ -133,7 +133,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	129.6547
 My 	227.4832
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	131.4867
 T	3421 w=4.5776	(nil)
@@ -176,7 +176,7 @@ My 	285.3548
 T	2765 w=4.9200	(nil)
 Mx 	104.6983
 My 	287.4548
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	17 w=3.7200	(nil)
 Mx 	114.8483
 My 	285.3548
@@ -189,7 +189,7 @@ My 	300.1048
 T	2765 w=4.9200	(nil)
 Mx 	104.6855
 My 	302.2048
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2758 w=3.7328	(nil)
 Mx 	114.8483
 My 	300.1048
@@ -203,7 +203,7 @@ Mx 	140.6728
 T	2765 w=4.9200	(nil)
 Mx 	145.2328
 My 	302.2048
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2758 w=3.7328	(nil)
 Mx 	148.9656
 T	2088 w=5.1840	(nil)
@@ -246,7 +246,7 @@ Mx 	146.0615
 T	2750 w=3.8100	(nil)
 Mx 	149.8715
 My 	341.0405
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	151.7035
 T	3421 w=4.5776	(nil)

diff --git a/tests/feat-math-display-unnumbered.expected b/tests/feat-math-display-unnumbered.expected
@@ -12,7 +12,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	135.7213
 My 	47.6655
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	137.5533
 T	3421 w=4.5776	(nil)
@@ -43,7 +43,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	135.7213
 My 	105.2660
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	137.5533
 T	3421 w=4.5776	(nil)
@@ -76,7 +76,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	135.7213
 My 	162.8665
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	137.5533
 T	3421 w=4.5776	(nil)
@@ -115,7 +115,7 @@ Set font 	Libertinus Math;10;400;Regular;normal;;;LTR
 T	2750 w=3.8100	(nil)
 Mx 	135.7213
 My 	220.4670
-Set font 	Libertinus Math;8;400;Regular;normal;;;LTR
+Set font 	Libertinus Math;8;400;Regular;normal;+ssty=1;;LTR
 T	2753 w=1.8320	(nil)
 Mx 	137.5533
 T	3421 w=4.5776	(nil)