initial commit

widow-assist.lua

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+-- Use method aliases for better performance
+local nodecopy = node.copy
+local nodecopylist = node.copy_list
+local nodetail = node.tail
+local nodeinsertbefore = node.insert_before
+local nodeinsertafter = node.insert_after
+local nodetraverseid = node.traverse_id
+
+-- Get node ids from their names
+local HLIST = node.id("hlist")
+local WHAT = node.id("whatsit")
+local COL = node.subtype("pdf_colorstack")
+
+-- Make nodes for beginning and end of colored regions
+local color_p1 = node.new(WHAT,COL)
+local color_p1s = node.new(WHAT,COL)
+local color_m1 = node.new(WHAT,COL)
+local color_pm1 = node.new(WHAT,COL)
+local color_pm1s = node.new(WHAT,COL)
+local color_pop = node.new(WHAT,COL)
+color_p1.stack = 0
+color_p1.command = 1
+color_p1.data = "0 0 1 rg" -- PDF code for RGB blue
+color_p1s.stack = 0
+color_p1s.command = 1
+color_p1s.data = "0 0.7 0.7 rg" -- PDF code for RGB dark cyan
+color_m1.stack = 0
+color_m1.command = 1
+color_m1.data = "1 0 0 rg" -- PDF code for RGB red
+color_pm1.stack = 0
+color_pm1.command = 1
+color_pm1.data = "1 0 1 rg" -- PDF code for RGB magenta
+color_pm1s.stack = 0
+color_pm1s.command = 1
+color_pm1s.data = "1 .5 .5 rg" -- PDF code for RGB pink
+color_pop.stack = 0
+color_pop.command = 2
+
+-- Color to use for last line in the next post-linebreak filter call (nil = no color)
+local LastLineColor = nil
+
+-- Function to color the last line in the given list
+local color_last_line = function (n)
+    -- Get the last hlist in the given list
+    local lastLine
+    for line in nodetraverseid(HLIST, n) do
+        lastLine = line
+    end
+
+    -- Surround it with color start/stop
+    lastLine.head = nodeinsertbefore(lastLine.head, lastLine.head, nodecopy(LastLineColor))
+    nodeinsertafter(lastLine.head, nodetail(lastLine.head), nodecopy(color_pop))
+end
+
+-- Callback to check if changing the looseness by +-1 would affect the line count
+local pre_linebreak_test_looseness = function (head, groupeCode)
+    -- Disable underfull and overfull boxes reporting
+    luatexbase.add_to_callback("hpack_quality", function() end, "hpqfilter")
+    luatexbase.add_to_callback("vpack_quality", function() end, "vpqfilter")
+
+    -- Build a copy of the paragraph normally
+    local n, i = tex.linebreak(nodecopylist(head))
+
+    -- Build a copy of the paragraph with increased looseness and default emergency stretch
+    local nP1s, iP1s = tex.linebreak(nodecopylist(head), {looseness=tex.looseness+1})
+
+    local nP1, iP1
+    if iP1s.prevgraf > i.prevgraf then
+        -- It worked with the default emergency stretch, let's try without
+        nP1, iP1 = tex.linebreak(nodecopylist(head), {looseness=tex.looseness+1, emergencystretch=0})
+    else
+        -- Didn't work with emergency stretch, no point to try without
+        nP1, iP1 = n, i
+    end
+
+    -- Build a copy of the paragraph with decreased looseness
+    local nM1, iM1 = tex.linebreak(nodecopylist(head), {looseness=tex.looseness-1})
+
+    -- Reenable underfull and overfull boxes reporting
+    luatexbase.remove_from_callback("hpack_quality", "hpqfilter")
+    luatexbase.remove_from_callback("vpack_quality", "vpqfilter")
+
+    -- Set color to use in the post-linebreak callback
+    if iP1.prevgraf > i.prevgraf and iM1.prevgraf < i.prevgraf then
+        -- Both +1 and -1 looseness would work
+        LastLineColor = color_pm1
+    elseif iP1s.prevgraf > i.prevgraf and iM1.prevgraf < i.prevgraf then
+        -- Both +1 and -1 looseness would work, but +1 only with emergency stretch
+        LastLineColor = color_pm1s
+    elseif iP1.prevgraf > i.prevgraf then
+        -- Only +1 looseness would work
+        LastLineColor = color_p1
+    elseif iP1s.prevgraf > i.prevgraf then
+        -- Only +1 looseness would work and only thanks to the emergency stretch
+        LastLineColor = color_p1s
+    elseif iM1.prevgraf < i.prevgraf then
+        -- Only -1 looseness would work
+        LastLineColor = color_m1
+    else
+        LastLineColor = nil
+    end
+
+    return true
+end
+
+-- Callback to colorize the last line of the paragraph when ColorLastLine is true
+local post_linebreak_color_last_line = function (head, groupcode)
+    if LastLineColor then
+        color_last_line(head)
+    end
+    return true
+end
+
+-- Register callbacks
+luatexbase.add_to_callback("pre_linebreak_filter", pre_linebreak_test_looseness, "pre_linebreak_test_looseness")
+luatexbase.add_to_callback("post_linebreak_filter", post_linebreak_color_last_line, "post_linebreak_color_last_line")