summaryrefslogtreecommitdiff
path: root/texmf-dist/tex/harftex/base/harf-node.lua
blob: 466db2ac40d86de661bbb4900932766a4ac1cf29 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
local module = {
  name        = "harf-node",
  description = "Harf text shaping",
  version     = "0.4.2",
  date        = "2019-09-07",
  license     = "GPL v2.0"
}
luatexbase.provides_module(module)

local hb = require("harf-base")

local assert            = assert
local next              = next
local tonumber          = tonumber
local type              = type
local format            = string.format
local open              = io.open
local tableinsert       = table.insert
local tableremove       = table.remove
local ostmpname         = os.tmpname
local osremove          = os.remove

local direct            = node.direct
local tonode            = direct.tonode
local todirect          = direct.todirect
local traverse          = direct.traverse
local traverseid        = direct.traverse_id
local insertbefore      = direct.insert_before
local insertafter       = direct.insert_after
local protectglyph      = direct.protect_glyph
local newnode           = direct.new
local copynode          = direct.copy
local removenode        = direct.remove
local copynodelist      = direct.copy_list
local isglyph           = direct.is_glyph

local getattrs          = direct.getattributelist
local setattrs          = direct.setattributelist
local getchar           = direct.getchar
local setchar           = direct.setchar
local getdir            = direct.getdir
local setdir            = direct.setdir
local getdata           = direct.getdata
local setdata           = direct.setdata
local getfont           = direct.getfont
local setfont           = direct.setfont
local getfield          = direct.getfield
local setfield          = direct.setfield
local getid             = direct.getid
local getkern           = direct.getkern
local setkern           = direct.setkern
local getnext           = direct.getnext
local setnext           = direct.setnext
local getoffsets        = direct.getoffsets
local setoffsets        = direct.setoffsets
local getproperty       = direct.getproperty
local setproperty       = direct.setproperty
local getprev           = direct.getprev
local setprev           = direct.setprev
local getsubtype        = direct.getsubtype
local setsubtype        = direct.setsubtype
local getwidth          = direct.getwidth
local setwidth          = direct.setwidth

local getpre            = function (n) return getfield(n, "pre")        end
local setpre            = function (n, v)     setfield(n, "pre", v)     end
local getpost           = function (n) return getfield(n, "post")       end
local setpost           = function (n, v)     setfield(n, "post", v)    end
local getrep            = function (n) return getfield(n, "replace")    end
local setrep            = function (n, v)     setfield(n, "replace", v) end

local imgnode           = img.node

local disc_t            = node.id("disc")
local glue_t            = node.id("glue")
local glyph_t           = node.id("glyph")
local dir_t             = node.id("dir")
local kern_t            = node.id("kern")
local localpar_t        = node.id("local_par")
local whatsit_t         = node.id("whatsit")
local pdfliteral_t      = node.subtype("pdf_literal")
local pdfcolorstack_t   = node.subtype("pdf_colorstack")

local explicitdisc_t    = 1
local fontkern_t        = 0
local italiccorr_t      = 3
local regulardisc_t     = 3
local spaceskip_t       = 13

local getscript         = hb.unicode.script

local common_s          = hb.Script.new("Zyyy")
local inherited_s       = hb.Script.new("Zinh")
local unknown_s         = hb.Script.new("Zzzz")
local latn_s            = hb.Script.new("Latn")

local invalid_l         = hb.Language.new()

local dir_ltr           = hb.Direction.new("ltr")
local dir_rtl           = hb.Direction.new("rtl")
local fl_unsafe         = hb.Buffer.GLYPH_FLAG_UNSAFE_TO_BREAK

local startactual_p     = "startactualtext"
local endactual_p       = "endactualtext"
local color_p           = "color"
local string_p          = "string"

-- Simple table copying function.
local function copytable(old)
  local new = {}
  for k, v in next, old do
    if type(v) == "table" then v = copytable(v) end
    new[k] = v
  end
  return new
end

-- Set and get properties from our private `harf` subtable.
local function setprop(n, prop, value)
  local props = getproperty(n)
  if not props then
    props = {}
    setproperty(n, props)
  end
  props.harf = props.harf or {}
  props.harf[prop] = value
end

-- New kern node of amount `v`, inheriting the properties/attributes of `n`.
local function newkern(v, n)
  local kern = newnode(kern_t)
  local props = getproperty(n)
  local attrs = getattrs(n)
  if props then
    setproperty(kern, copytable(props))
  end
  if attrs then
    setattrs(kern, copynodelist(attrs))
  end

  setkern(kern, v)
  return kern
end

local function insertkern(head, current, kern, rtl)
  if rtl then
    head = insertbefore(head, current, kern)
  else
    head, current = insertafter(head, current, kern)
  end
  return head, current
end

-- Convert list of integers to UTF-16 hex string used in PDF.
local function to_utf16_hex(uni)
  if uni < 0x10000 then
    return format("%04X", uni)
  else
    uni = uni - 0x10000
    local hi = 0xD800 + (uni // 0x400)
    local lo = 0xDC00 + (uni % 0x400)
    return format("%04X%04X", hi, lo)
  end
end

local paired_open = {
  [0x0028] = 0x0029, [0x003c] = 0x003e, [0x005b] = 0x005d, [0x007b] = 0x007d,
  [0x00ab] = 0x00bb, [0x2018] = 0x2019, [0x201c] = 0x201d, [0x2039] = 0x203a,
  [0x3008] = 0x3009, [0x300a] = 0x300b, [0x300c] = 0x300d, [0x300e] = 0x300f,
  [0x3010] = 0x3011, [0x3014] = 0x3015, [0x3016] = 0x3017, [0x3018] = 0x3019,
  [0x301a] = 0x301b,
}

local paired_close = {
  [0x0029] = 0x0028, [0x003e] = 0x003c, [0x005d] = 0x005b, [0x007d] = 0x007b,
  [0x00bb] = 0x00ab, [0x2019] = 0x2018, [0x201d] = 0x201c, [0x203a] = 0x2039,
  [0x3009] = 0x3008, [0x300b] = 0x300a, [0x300d] = 0x300c, [0x300f] = 0x300e,
  [0x3011] = 0x3010, [0x3015] = 0x3014, [0x3017] = 0x3016, [0x3019] = 0x3018,
  [0x301b] = 0x301a,
}

local process

local trep = hb.texrep

local function itemize(head, direction)
  -- Collect character properties (font, direction, script) and resolve common
  -- and inherited scripts. Pre-requisite for itemization into smaller runs.
  local props, nodes, codes = {}, {}, {}
  local dirstack, pairstack = {}, {}
  local currdir = direction or "TLT"
  local currfontid = nil

  for n in direct.traverse(head) do
    local id = getid(n)
    local code = 0xFFFC -- OBJECT REPLACEMENT CHARACTER
    local script = common_s
    local skip = false

    if id == glyph_t then
      currfontid = getfont(n)
      if getsubtype(n) > 255 then
        skip = true
      else
        code = getchar(n)
        script = getscript(code)
      end
    elseif id == glue_t and getsubtype(n) == spaceskip_t then
      code = 0x0020 -- SPACE
    elseif id == disc_t
      and (getsubtype(n) == explicitdisc_t  -- \-
        or getsubtype(n) == regulardisc_t)  -- \discretionary
    then
      code = 0x00AD -- SOFT HYPHEN
    elseif id == dir_t then
      local dir = getdir(n)
      if dir:sub(1, 1) == "+" then
        -- Push the current direction to the stack.
        tableinsert(dirstack, currdir)
        currdir = dir:sub(2)
      else
        assert(currdir == dir:sub(2))
        -- Pop the last direction from the stack.
        currdir = tableremove(dirstack)
      end
    elseif id == localpar_t then
      currdir = getdir(n)
    end

    local fontdata = currfontid and font.getfont(currfontid)
    local hbdata   = fontdata and fontdata.hb
    local options  = hbdata and hbdata.options
    local texlig   = options and options.texlig
    if texlig then
      local replacement = trep[code]
      if replacement then
        code = replacement
      end
    end

    if not hbdata then skip = true end

    -- Resolve common and inherited scripts. Inherited takes the script of the
    -- previous character. Common almost the same, but we tray to make paired
    -- characters (e.g. parentheses) to take the same script.
    if #props > 0 and (script == common_s or script == inherited_s) then
      script = props[#props].script
      -- Paired punctuation characters
      if paired_open[code] then
        tableinsert(pairstack, { code, script })
      elseif paired_close[code] then
        while #pairstack > 0 do
          local c = tableremove(pairstack)
          if c[1] == paired_close[code] then
            script = c[2]
            break
          end
        end
      end
    end

    -- If script is not resolved yet, and the font has a "script" option, use
    -- it.
    if (script == common_s or script == inherited_s) and hbdata then
      local options = hbdata.options
      script = options.script and hb.Script.new(options.script) or script
    end

    codes[#codes + 1] = code
    nodes[#nodes + 1] = n
    props[#props + 1] = {
      font = currfontid,
      -- XXX handle RTT and LTL.
      dir = currdir == "TRT" and dir_rtl or dir_ltr,
      script = script,
      skip = skip,
    }
  end

  for i = #props - 1, 1, -1 do
    -- If script is not resolved yet, use that of the next character.
    if props[i].script == common_s or props[i].script == inherited_s then
      props[i].script = props[i + 1].script
    end
  end

  -- Split into a list of runs, each has the same font, direction and script.
  -- TODO: itemize by language as well.
  local runs = {}
  local currfontid, currdir, currscript, currskip = nil, nil, nil, nil
  for i, prop in next, props do
    local fontid = prop.font
    local dir = prop.dir
    local script = prop.script
    local skip = prop.skip

    -- Start a new run if there is a change in properties.
    if fontid ~= currfontid or
       dir ~= currdir or
       script ~= currscript or
       skip ~= currskip then
      runs[#runs + 1] = {
        start = i,
        len = 0,
        font = fontid,
        dir = dir,
        script = script,
        skip = skip,
        nodes = nodes,
        codes = codes,
      }
    end

    runs[#runs].len = runs[#runs].len + 1

    currfontid = fontid
    currdir = dir
    currscript = script
    currskip = skip
  end

  return runs
end

-- Find how many characters are part of this glyph.
--
-- The first return value is the number of characters, with 0 meaning it is
-- inside a multi-glyph cluster
--
-- The second return value is the number of glyph in this cluster.
--
local function chars_in_glyph(i, glyphs, stop)
  local nchars, nglyphs = 0, 0
  local cluster = glyphs[i].cluster

  -- Glyph is not the first in cluster
  if glyphs[i - 1] and glyphs[i - 1].cluster == cluster then
    return 0, 0
  end

  -- Find the last glyph in this cluster.
  while glyphs[i + nglyphs] and glyphs[i + nglyphs].cluster == cluster do
    nglyphs = nglyphs + 1
  end

  -- The number of characters is the diff between the next cluster in this one.
  if glyphs[i + nglyphs] then
    nchars = glyphs[i + nglyphs].cluster - cluster
  else
    -- This glyph cluster in the last in the run.
    nchars = stop - cluster - 1
  end

  return nchars, nglyphs
end

-- Check if it is not safe to break before this glyph.
local function unsafetobreak(glyph, nodes)
  return glyph
     and glyph.flags
     and glyph.flags & fl_unsafe
     -- Discretionary nodes can’t contain glue, so stop at first glue as well.
     -- This is incorrect, but I don’t have a better idea.
     and getid(nodes[glyph.cluster + 1]) ~= glue_t
end

local shape

-- Make s a sub run, used by discretionary nodes.
local function makesub(run, start, stop, nodelist)
  local nodes = run.nodes
  local codes = run.codes
  local start = start
  local stop = stop
  local subnodes, subcodes = {}, {}
  for i = start, stop do
    if getid(nodes[i]) ~= disc_t then
      subnodes[#subnodes + 1] = copynode(nodes[i])
      subcodes[#subcodes + 1] = codes[i]
    end
  end
  -- Prepend any existing nodes to the list.
  for n in traverse(nodelist) do
    subnodes[#subnodes + 1] = n
    subcodes[#subcodes + 1] = getchar(n)
  end
  local subrun = {
    start = 1,
    len = #subnodes,
    font = run.font,
    script = run.script,
    dir = run.dir,
    fordisc = true,
    nodes = subnodes,
    codes = subcodes,
  }
  return { glyphs = shape(subrun), run = subrun }
end

-- Main shaping function that calls HarfBuzz, and does some post-processing of
-- the output.
shape = function(run)
  local nodes = run.nodes
  local codes = run.codes
  local offset = run.start
  local len = run.len
  local fontid = run.font
  local dir = run.dir
  local script = run.script
  local lang = run.lang
  local fordisc = run.fordisc

  local fontdata = font.getfont(fontid)
  local hbdata = fontdata.hb
  local features = hbdata.features
  local options = hbdata.options
  local palette = hbdata.palette
  local hbshared = hbdata.shared
  local hbfont = hbshared.font
  local hbface = hbshared.face

  local lang = lang or options.language or invalid_l
  local shapers = options.shaper and { options.shaper } or {}

  local buf = hb.Buffer.new()
  buf:set_direction(dir)
  buf:set_script(script)
  buf:set_language(lang)
  buf:set_cluster_level(buf.CLUSTER_LEVEL_MONOTONE_CHARACTERS)
  buf:add_codepoints(codes, offset - 1, len)

  local hscale = hbdata.hscale
  local vscale = hbdata.vscale
  hbfont:set_scale(hscale, vscale)

  if hb.shape_full(hbfont, buf, features, shapers) then
    -- The engine wants the glyphs in logical order, but HarfBuzz outputs them
    -- in visual order, so we reverse RTL buffers.
    if dir:is_backward() then buf:reverse() end

    local glyphs = buf:get_glyphs()

    -- If the font has COLR/CPAL tables, decompose each glyph to its color
    -- layers and set the color from the palette.
    if palette then
      for i, glyph in next, glyphs do
        local gid = glyph.codepoint
        local layers = hbface:ot_color_glyph_get_layers(gid)
        if layers then
          -- Remove this glyph, we will use its layers.
          tableremove(glyphs, i)
          for j, layer in next, layers do
            -- All glyphs but the last use 0 advance so that the layers
            -- overlap.
            local xadavance, yadvance = nil, nil
            if dir:is_backward() then
              x_advance = j == 1 and glyph.x_advance or 0
              y_advance = j == 1 and glyph.y_advance or 0
            else
              x_advance = j == #layers and glyph.x_advance or 0
              y_advance = j == #layers and glyph.y_advance or 0
            end
            tableinsert(glyphs, i + j - 1, {
              codepoint = layer.glyph,
              cluster = glyph.cluster,
              x_advance = x_advance,
              y_advance = y_advance,
              x_offset = glyph.x_offset,
              y_offset = glyph.y_offset,
              flags = glyph.flags,
              -- color_index has a special value, 0x10000, that mean use text
              -- color, we don’t check for it here explicitly since we will
              -- get nil anyway.
              color = palette[layer.color_index],
            })
          end
        end
      end
    end

    for i, glyph in next, glyphs do
      local nodeindex = glyph.cluster + 1
      local nchars, nglyphs = chars_in_glyph(i, glyphs, offset + len)
      glyph.nchars, glyph.nglyphs = nchars, nglyphs

      -- Calculate the Unicode code points of this glyph. If nchars is zero
      -- then this is a glyph inside a complex cluster and will be handled with
      -- the start of its cluster.
      if nchars > 0 then
        local hex = ""
        local str = ""
        for j = 0, nchars - 1 do
          local id = getid(nodes[nodeindex + j])
          if id == glyph_t or id == glue_t then
            local code = codes[nodeindex + j]
            hex = hex..to_utf16_hex(code)
            str = str..utf8.char(code)
          end
        end
        glyph.tounicode = hex
        glyph.string = str
      end

      -- Find if we have a discretionary inside a ligature, if nchars less than
      -- two then either this is not a ligature or there is no discretionary
      -- involved.
      if nchars > 2 and not fordisc then
        local discindex = nil
        for j = nodeindex, nodeindex + nchars - 1 do
          if codes[j] == 0x00AD then
            discindex = j
            break
          end
        end
        if discindex then
          -- Discretionary found.
          local disc = nodes[discindex]
          local startindex, stopindex = nil, nil
          local startglyph, stopglyph = nil, nil

          -- Find the previous glyph that is safe to break at.
          startglyph = i
          while unsafetobreak(glyphs[startglyph], nodes) do
            startglyph = startglyph - 1
          end
          -- Get the corresponding character index.
          startindex = glyphs[startglyph].cluster + 1

          -- Find the next glyph that is safe to break at.
          stopglyph = i + nglyphs
          while unsafetobreak(glyphs[stopglyph], nodes) do
            stopglyph = stopglyph + 1
          end
          -- We also want the last char in the previous glyph, so no +1 below.
          stopindex = glyphs[stopglyph].cluster
          -- We break up to stop glyph but not including it, so the -1 below.
          stopglyph = stopglyph - 1

          -- Mark these glyph for skipping since they will be replaced by the
          -- discretionary fields.
          for j = startglyph, stopglyph do
            glyphs[j].skip = true
          end

          local pre, post, rep = getpre(disc), getpost(disc), getrep(disc)
          glyph.disc = disc
          glyph.replace = makesub(run, startindex, stopindex, rep)
          glyph.pre = makesub(run, startindex, discindex - 1, pre)
          glyph.post = makesub(run, discindex + 1, stopindex, post)
        end
      end
    end
    return glyphs
  end

  return {}
end

local function color_to_rgba(color)
  local r = color.red   / 255
  local g = color.green / 255
  local b = color.blue  / 255
  local a = color.alpha / 255
  if a ~= 1 then
    -- XXX: alpha
    return format('%s %s %s rg', r, g, b)
  else
    return format('%s %s %s rg', r, g, b)
  end
end

-- Cache of color glyph PNG data for bookkeeping, only because I couldn’t
-- figure how to make the engine load the image from the binary data directly.
local pngcache = {}
local function cachedpng(data)
  local hash = md5.sumhexa(data)
  local path = pngcache[hash]
  if not path then
    path = ostmpname()
    local file = open(path, "wb")
    file:write(data)
    file:close()
    pngcache[hash] = path
  end
  return path
end

-- Convert glyphs to nodes and collect font characters.
local function tonodes(head, current, run, glyphs, color)
  local nodes = run.nodes
  local dir = run.dir
  local fontid = run.font
  local fontdata = font.getfont(fontid)
  local characters = fontdata.characters
  local hbdata = fontdata.hb
  local hbshared = hbdata.shared
  local hbfont = hbshared.font
  local fontglyphs = hbshared.glyphs
  local rtl = dir:is_backward()

  local tracinglostchars = tex.tracinglostchars
  local tracingonline = tex.tracingonline

  local scale = hbdata.scale
  local letterspace = hbdata.letterspace

  local haspng = hbshared.haspng
  local fonttype = hbshared.fonttype

  for i, glyph in next, glyphs do
    local index = glyph.cluster + 1
    local gid = glyph.codepoint
    local char = hb.CH_GID_PREFIX + gid
    local n = nodes[index]
    local id = getid(n)
    local nchars, nglyphs = glyph.nchars, glyph.nglyphs

    -- If this glyph is part of a complex cluster, then copy the node as
    -- more than one glyph will use it.
    if nglyphs < 1 or nglyphs > 1 then
      n = copynode(nodes[index])
    end

    if color then
      setprop(n, color_p, color)
    end

    if glyph.disc then
      -- For discretionary the glyph itself is skipped and a discretionary node
      -- is output in place of it.
      local disc = glyph.disc
      local rep, pre, post = glyph.replace, glyph.pre, glyph.post

      setrep(disc, tonodes(nil, nil, rep.run, rep.glyphs, color))
      setpre(disc, tonodes(nil, nil, pre.run, pre.glyphs, color))
      setpost(disc, tonodes(nil, nil, post.run, post.glyphs, color))

      head, current = insertafter(head, current, disc)
    elseif not glyph.skip then
      if glyph.color then
        setprop(n, color_p, color_to_rgba(glyph.color))
      end

      if id == glyph_t then
        local fontglyph = fontglyphs[gid]

        local pngblob = fontglyph.png
        if haspng and not pngblob then
          pngblob = hbfont:ot_color_glyph_get_png(gid)
          fontglyph.png = pngblob
        end
        local character = characters[char]
        if pngblob then
          -- Color bitmap font, extract the PNG data and insert it in the node
          -- list.
          local data = pngblob:get_data()
          local path = cachedpng(data)

          local image = imgnode {
            filename  = path,
            width     = character.width,
            height    = character.height,
            depth     = character.depth,
          }
          head, current = insertafter(head, current, todirect(image))
          if fonttype then
            -- Color bitmap font with glyph outlines. Insert negative kerning
            -- as we will insert the glyph node below (to help with text
            -- copying) and want the bitmap and the glyph to take the same
            -- advance width.
            local kern = newkern(-character.width, n)
            head, current = insertkern(head, current, kern, rtl)
          end
        end
        if pngblob and not fonttype then
          -- Color bitmap font with no glyph outlines, and has a bitmap for
          -- this glyph. No further work is needed.
        elseif haspng and not fonttype then
          -- Color bitmap font with no glyph outlines (like Noto
          -- Color Emoji) but has no bitmap for current glyph (most likely
          -- `.notdef` glyph). The engine does not know how to embed such
          -- fonts, so we don’t want them to reach the backend as it will cause
          -- a fatal error. We use `nullfont` instead.  That is a hack, but I
          -- think it is good enough for now.
          -- We insert the glyph node and move on, no further work is needed.
          setfont(n, 0)
          head, current = insertafter(head, current, n)
        else
          local oldcharacter = characters[getchar(n)]
          -- If the glyph index of current font character is the same as shaped
          -- glyph, keep the node char unchanged. Helps with primitives that
          -- take characters as input but actually work on glyphs, like
          -- `\rpcode`.
          if not oldcharacter or character.index ~= oldcharacter.index then
            setchar(n, char)
          end
          local xoffset = (rtl and -glyph.x_offset or glyph.x_offset) * scale
          local yoffset = glyph.y_offset * scale
          setoffsets(n, xoffset, yoffset)
          protectglyph(n)
          head, current = insertafter(head, current, n)

          local x_advance = glyph.x_advance + letterspace
          local width = fontglyph.width
          if width ~= x_advance then
            -- The engine always uses the glyph width from the font, so we need
            -- to insert a kern node if the x advance is different.
            local kern = newkern((x_advance - width) * scale, n)
            head, current = insertkern(head, current, kern, rtl)
          end

          fontglyph.used = true

          -- The engine will use this string when printing a glyph node e.g. in
          -- overfull messages, otherwise it will be trying to print our
          -- invalid pseudo Unicode code points.
          -- If the string is empty it means this glyph is part of a larger
          -- cluster and we don’t to print anything for it as the first glyph
          -- in the cluster will have the string of the whole cluster.
          setprop(n, string_p, glyph.string or "")

          -- Handle PDF text extraction:
          -- * Find how many characters in this cluster and how many glyphs,
          -- * If there is more than 0 characters
          --   * One glyph: one to one or one to many mapping, can be
          --     represented by font’s /ToUnicode
          --   * More than one: many to one or many to many mapping, can be
          --     represented by /ActualText spans.
          -- * If there are zero characters, then this glyph is part of complex
          --   cluster that will be covered by an /ActualText span.
          local tounicode = glyph.tounicode
          if tounicode then
            if nglyphs == 1 and not fontglyph.tounicode then
              fontglyph.tounicode = tounicode
            elseif tounicode ~= fontglyph.tounicode then
              setprop(n, startactual_p, tounicode)
              glyphs[i + nglyphs - 1].endactual = true
            end
          end
          if glyph.endactual then
            setprop(n, endactual_p, true)
          end
        end
      elseif id == glue_t and getsubtype(n) == spaceskip_t then
        -- If the glyph advance is different from the font space, then a
        -- substitution or positioning was applied to the space glyph changing
        -- it from the default, so reset the glue using the new advance.
        -- We are intentionally not comparing with the existing glue width as
        -- spacing after the period is larger by default in TeX.
        local width = (glyph.x_advance + letterspace) * scale
        if fontdata.parameters.space ~= width then
          setwidth(n, width)
          setfield(n, "stretch", width / 2)
          setfield(n, "shrink", width / 3)
        end
        head, current = insertafter(head, current, n)
      elseif id == kern_t and getsubtype(n) == italiccorr_t then
        -- If this is an italic correction node and the previous node is a
        -- glyph, update its kern value with the glyph’s italic correction.
        -- I’d have expected the engine to do this, but apparently it doesn’t.
        -- May be it is checking for the italic correction before we have had
        -- loaded the glyph?
        local prevchar, prevfontid = isglyph(current)
        if prevchar and prevchar > 0 then
          local prevfontdata = font.getfont(prevfontid)
          local prevcharacters = prevfontdata and prevfontdata.characters
          local italic = prevcharacters and prevcharacters[prevchar].italic
          if italic then
            setkern(n, italic)
          end
        end
        head, current = insertafter(head, current, n)
      elseif id == disc_t then
        assert(nglyphs == 1)
        -- The simple case of a discretionary that is not part of a complex
        -- cluster. We only need to make sure kerning before the hyphenation
        -- point is dropped when a line break is inserted here.
        --
        -- TODO: nothing as simple as it sounds, we need to handle this like
        -- the other discretionary handling, otherwise the discretionary
        -- contents do not interact with the surrounding (e.g. no ligatures or
        -- kerning) as it should.
        if current and getid(current) == kern_t and getsubtype(current) == fontkern_t then
          setprev(current, nil)
          setnext(current, nil)
          setfield(n, "replace", current)
          head, current = removenode(head, current)
        end
        local pre, post, rep = getpre(n), getpost(n), getrep(n)
        setfield(n, "pre", process(pre, direction))
        setfield(n, "post", process(post, direction))
        setfield(n, "replace", process(rep, direction))

        head, current = insertafter(head, current, n)
      else
        head, current = insertafter(head, current, n)
      end
    end
  end

  return head, current
end

local function validate_color(s)
  local r = tonumber(s:sub(1, 2), 16)
  local g = tonumber(s:sub(3, 4), 16)
  local b = tonumber(s:sub(5, 6), 16)
  if not (r and g and b) then return end
  if #s == 8 then
    local a = tonumber(s:sub(7, 8), 16)
    if not a then return end
  end
  return s
end

local function hex_to_rgba(s)
  if not validate_color(s) then return end
  local r = tonumber(s:sub(1, 2), 16) / 255
  local g = tonumber(s:sub(3, 4), 16) / 255
  local b = tonumber(s:sub(5, 6), 16) / 255
  if #s == 8 then
    local a = tonumber(s:sub(7, 8), 16) / 255
    -- XXX: alpha
    return format('%s %s %s rg', r, g, b)
  else
    return format('%s %s %s rg', r, g, b)
  end
end

local function shape_run(head, current, run)
  if not run.skip then
    -- Font loaded with our loader and an HarfBuzz face is present, do our
    -- shaping.
    local fontid = run.font
    local fontdata = font.getfont(fontid)
    local options = fontdata.hb.options
    local color = options and options.color and hex_to_rgba(options.color)

    local glyphs = shape(run)
    head, current = tonodes(head, current, run, glyphs, color)
  else
    -- Not shaping, insert the original node list of of this run.
    local nodes = run.nodes
    local offset = run.start
    local len = run.len
    for i = offset, offset + len - 1 do
      head, current = insertafter(head, current, nodes[i])
    end
  end

  return head, current
end

process = function(head, direction)
  local newhead, current = nil, nil
  local runs = itemize(head, direction)

  for _, run in next, runs do
    newhead, current = shape_run(newhead, current, run)
  end

  return newhead or head
end

local function process_nodes(head, groupcode, size, packtype, direction)
  local head = todirect(head)

  -- Check if any fonts are loaded by us and then process the whole node list,
  -- we will take care of skipping fonts we did not load later, otherwise
  -- return unmodified head.
  for n in traverseid(glyph_t, head) do
    local fontid = getfont(n)
    local fontdata = font.getfont(fontid)
    local hbdata = fontdata and fontdata.hb
    if hbdata then
      head = process(head, direction)
      break
    end
  end

  -- Nothing to do; no glyphs or no HarfBuzz fonts.
  return tonode(head)
end

local function pdfdirect(data)
  local n = newnode(whatsit_t, pdfliteral_t)
  setfield(n, "mode", 2) -- direct
  setdata(n, data)
  return n
end

local function pdfcolor(color)
  local c = newnode(whatsit_t, pdfcolorstack_t)
  setfield(c, "stack", 0)
  setfield(c, "command", color and 1 or 2) -- 1: push, 2: pop
  setfield(c, "data", color)
  return c
end

local function post_process(head, currentcolor)
  for n in traverse(head) do
    local props = getproperty(n)
    local harfprops = props and props.harf

    local startactual, endactual, color
    if harfprops then
      startactual = harfprops[startactual_p]
      endactual = harfprops[endactual_p]
      color = harfprops[color_p]
    end

    if currentcolor and currentcolor ~= color then
      -- Pop current color.
      currentcolor = nil
      head = insertbefore(head, n, pdfcolor(currentcolor))
    end

    if currentcolor ~= color then
      -- Push new color.
      currentcolor = color
      head = insertbefore(head, n, pdfcolor(currentcolor))
    end

    if startactual then
      local actualtext = "/Span<</ActualText<FEFF"..startactual..">>>BDC"
      head = insertbefore(head, n, pdfdirect(actualtext))
    end

    if endactual then
      head = insertafter(head, n, pdfdirect("EMC"))
    end

    local replace = getfield(n, "replace")
    if replace then
      setfield(n, "replace", post_process(replace, currentcolor))
    end

    local subhead = getfield(n, "head")
    if subhead then
      setfield(n, "head", post_process(subhead, currentcolor))
    end
  end
  return head
end

local function post_process_nodes(head, groupcode)
  return tonode(post_process(todirect(head)))
end

local function run_cleanup()
  -- Remove temporary PNG files that we created, if any.
  for _, path in next, pngcache do
    osremove(path)
  end
end

local function set_tounicode()
  for fontid, fontdata in font.each() do
    local hbdata = fontdata.hb
    if hbdata and fontid == pdf.getfontname(fontid) then
      local characters = fontdata.characters
      local newcharacters = {}
      local glyphs = hbdata.shared.glyphs
      for gid = 0, #glyphs do
        local glyph = glyphs[gid]
        if glyph.used then
          local tounicode = glyph.tounicode or "FFFD"
          local character = characters[gid + hb.CH_GID_PREFIX]
          newcharacters[gid + hb.CH_GID_PREFIX] = character
          character.tounicode = tounicode
          character.used = true
        end
      end
      font.addcharacters(fontid, { characters = newcharacters })
    end
  end
end

local function get_glyph_string(n)
  local n = todirect(n)
  local props = getproperty(n)
  props = props and props.harf
  return props and props[string_p] or nil
end

return {
  process = process_nodes,
  post_process = post_process_nodes,
  cleanup = run_cleanup,
  set_tounicode = set_tounicode,
  get_glyph_string = get_glyph_string,
}