Support 'opbd' (OpenType protrusion) feature

Code scrapped from ConTeXt, AFAIK, no font implements OpenType optical
bounds (on of Linux Libertine font has traces of it), but I plan to use
it in my fonts. The committed feature file is prepared for Pagella, we
can later have font specific feature files like this.

1 files changed, 110 insertions, 11 deletions

diff --git a/otfl-font-dum.lua b/otfl-font-dum.lua
index 8e13b5b..1d79ab1 100644
--- a/otfl-font-dum.lua
+++ b/otfl-font-dum.lua
@@ -155,20 +155,119 @@ fonts.protrusions.setups = fonts.protrusions.setups or { }
 
 local setups  = fonts.protrusions.setups
 
+-- As this is experimental code, users should not depend on it. The
+-- implications are still discussed on the ConTeXt Dev List and we're
+-- not sure yet what exactly the spec is (the next code is tested with
+-- a gyre font patched by / fea file made by Khaled Hosny). The double
+-- trick should not be needed it proper hanging punctuation is used in
+-- which case values < 1 can be used.
+--
+-- preferred (in context, usine vectors):
+--
+-- \definefontfeature[whatever][default][mode=node,protrusion=quality]
+--
+-- using lfbd and rtbd, with possibibility to enable only one side :
+--
+-- \definefontfeature[whocares][default][mode=node,protrusion=yes,  opbd=yes,script=latn]
+-- \definefontfeature[whocares][default][mode=node,protrusion=right,opbd=yes,script=latn]
+--
+-- idem, using multiplier
+--
+-- \definefontfeature[whocares][default][mode=node,protrusion=2,opbd=yes,script=latn]
+-- \definefontfeature[whocares][default][mode=node,protrusion=double,opbd=yes,script=latn]
+--
+-- idem, using named feature file (less frozen):
+--
+-- \definefontfeature[whocares][default][mode=node,protrusion=2,opbd=yes,script=latn,featurefile=texgyrepagella-regularxx.fea]
+
+local function map_opbd_onto_protrusion(tfmdata,value,opbd)
+    local characters, descriptions = tfmdata.characters, tfmdata.descriptions
+    local otfdata = tfmdata.shared.otfdata
+    local singles = otfdata.shared.featuredata.gpos_single
+    local script, language = tfmdata.script, tfmdata.language
+    local done, factor, left, right = false, 1, 1, 1
+    local setup = setups[value]
+    if setup then
+        factor = setup.factor or 1
+        left   = setup.left   or 1
+        right  = setup.right  or 1
+    else
+        factor = tonumber(value) or 1
+    end
+    if opbd ~= "right" then
+        local validlookups, lookuplist = fonts.otf.collect_lookups(otfdata,"lfbd",script,language)
+        if validlookups then
+            for i=1,#lookuplist do
+                local lookup = lookuplist[i]
+                local data = singles[lookup]
+                if data then
+                    if trace_protrusion then
+                        logs.report("fonts","set left protrusion using lfbd lookup '%s'",lookup)
+                    end
+                    for k, v in next, data do
+                    --  local p = - v[3] / descriptions[k].width-- or 1 ~= 0 too but the same
+                        local p = - (v[1] / 1000) * factor * left
+                        characters[k].left_protruding = p
+                        if trace_protrusion then
+                            logs.report("opbd","lfbd -> %s -> 0x%05X (%s) -> %0.03f (%s)",lookup,k,utfchar(k),p,concat(v," "))
+                        end
+                    end
+                    done = true
+                end
+            end
+        end
+    end
+    if opbd ~= "left" then
+        local validlookups, lookuplist = fonts.otf.collect_lookups(otfdata,"rtbd",script,language)
+        if validlookups then
+            for i=1,#lookuplist do
+                local lookup = lookuplist[i]
+                local data = singles[lookup]
+                if data then
+                    if trace_protrusion then
+                        logs.report("fonts","set right protrusion using rtbd lookup '%s'",lookup)
+                    end
+                    for k, v in next, data do
+                    --  local p = v[3] / descriptions[k].width -- or 3
+                        local p = (v[1] / 1000) * factor * right
+                        characters[k].right_protruding = p
+                        if trace_protrusion then
+                            logs.report("opbd","rtbd -> %s -> 0x%05X (%s) -> %0.03f (%s)",lookup,k,utfchar(k),p,concat(v," "))
+                        end
+                    end
+                end
+                done = true
+            end
+        end
+    end
+    tfmdata.auto_protrude = done
+end
+
+-- The opbd test is just there because it was discussed on the
+-- context development list. However, the mentioned fxlbi.otf font
+-- only has some kerns for digits. So, consider this feature not
+-- supported till we have a proper test font.
+
 function fonts.initializers.common.protrusion(tfmdata,value)
     if value then
-        local setup = setups[value]
-        if setup then
-            local factor, left, right = setup.factor or 1, setup.left or 1, setup.right or 1
-            local emwidth = tfmdata.parameters.quad
-            tfmdata.auto_protrude = true
-            for i, chr in next, tfmdata.characters do
-                local v, pl, pr = setup[i], nil, nil
-                if v then
-                    pl, pr = v[1], v[2]
+        local opbd = tfmdata.shared.features.opbd
+        if opbd then
+            -- possible values: left right both yes no (experimental)
+            map_opbd_onto_protrusion(tfmdata,value,opbd)
+        elseif value then
+            local setup = setups[value]
+            if setup then
+                local factor, left, right = setup.factor or 1, setup.left or 1, setup.right or 1
+                local emwidth = tfmdata.parameters.quad
+                tfmdata.auto_protrude = true
+                for i, chr in next, tfmdata.characters do
+                    local v, pl, pr = setup[i], nil, nil
+                    if v then
+                        pl, pr = v[1], v[2]
+                    end
+                    if pl and pl ~= 0 then chr.left_protruding  = left *pl*factor end
+                    if pr and pr ~= 0 then chr.right_protruding = right*pr*factor end
                 end
-                if pl and pl ~= 0 then chr.left_protruding  = left *pl*factor end
-                if pr and pr ~= 0 then chr.right_protruding = right*pr*factor end
             end
         end
     end