[aux] fix \fontdimen8 hack

Addresses #341

This cleans up the font patching code we inherited from Fontspec. In
addition to treating the bitrot with an extra dose of fungicide, we also
make the process in which the final values are chosen more transparent.

1 files changed, 63 insertions, 31 deletions

diff --git a/src/luaotfload-auxiliary.lua b/src/luaotfload-auxiliary.lua
index 347d9f8..22f8201 100644
--- a/src/luaotfload-auxiliary.lua
+++ b/src/luaotfload-auxiliary.lua
@@ -177,40 +177,72 @@ Comment from fontspec:
 
 --doc]]--
 
+local capheight_reference_char = stringbyte "X" -- might be ‘M’, ‘Ж’, or ‘ξ’.
+
+local determine_capheight = function (fontdata)
+  local parameters = fontdata.parameters if not parameters then return false end
+  local characters = fontdata.characters if not characters then return false end
+  local refchar    = characters [capheight_reference_char]
+  if refchar then
+    return refchar.height
+  end
+  return false
+end
+
+local query_ascender = function (fontdata)
+  local parameters = fontdata.parameters if not parameters then return false end
+  local metadata   = fontdata.metadata   if not metadata   then return false end
+  local ascender   = metadata.ascender   if not ascender   then return false end
+  local units      = metadata.units      if units == 0     then return false end
+  local size       = parameters.size     if not size       then return false end
+  return ascender * size / units
+end
+
+local query_capheight = function (fontdata)
+  local parameters = fontdata.parameters if not parameters then return false end
+  local metadata   = fontdata.metadata   if not metadata   then return false end
+  local capheight  = metadata.capheight  if not capheight  then return false end
+  local units      = metadata.units      if units == 0     then return false end
+  local size       = parameters.size     if not size       then return false end
+  return capheight * size / units
+end
+
+local query_fontdimen8 = function (fontdata)
+  local parameters = fontdata.parameters if not parameters then return false end
+  local fontdimen8 = parameters [8]
+  if fontdimen8 then return fontdimen8 end
+  return false
+end
+
+local caphtfmt = function (ref, ht)
+  if not ht  then return "<none>"      end
+  if not ref then return tostring (ht) end
+  return stringformat ("%s(δ=%s)", ht, ht - ref)
+end
+
 local set_capheight = function (fontdata)
-    local shared     = fontdata.shared
-    local parameters = fontdata.parameters
-    local capheight
-    if    shared
-      and shared.rawdata.metadata
-      and shared.rawdata.metadata.pfminfo
-    then
-      local units_per_em   = parameters.units
-      local size           = parameters.size
-      local os2_capheight  = shared.rawdata.metadata.pfminfo.os2_capheight
-
-      if capheight and os2_capheight > 0 then
-        capheight = os2_capheight / units_per_em * size
-      else
-        local X8_str = stringbyte"X"
-        local X8_chr = fontdata.characters[X8_str]
-        if X8_chr then
-          capheight = X8_chr.height
-        else
-          capheight = parameters.ascender / units_per_em * size
-        end
-      end
-    else
-      local X8_str = stringbyte "X"
-      local X8_chr = fontdata.characters[X8_str]
-      if X8_chr then
-        capheight = X8_chr.height
-      end
+    if not fontdata then
+      logreport ("both", 0, "aux",
+                 "error: set_capheight() received garbage")
+      return
     end
+    local capheight_dimen8   = query_fontdimen8    (fontdata)
+    local capheight_alleged  = query_capheight     (fontdata)
+    local capheight_ascender = query_ascender      (fontdata)
+    local capheight_measured = determine_capheight (fontdata)
+    logreport ("term", 4, "aux",
+               "capht: param[8]=%s advertised=%s ascender=%s measured=%s",
+               tostring (capheight_dimen8),
+               caphtfmt (capheight_dimen8, capheight_alleged),
+               caphtfmt (capheight_dimen8, capheight_ascender),
+               caphtfmt (capheight_dimen8, capheight_measured))
+    if capheight_dimen8 then --- nothing to do
+      return
+    end
+
+    local capheight = capheight_alleged or capheight_ascender or capheight_measured
     if capheight then
-      --- is this legit? afaics there’s nothing else on the
-      --- array part of that table
-      fontdata.parameters[8] = capheight
+      fontdata.parameters [8] = capheight
     end
 end