hb.c

// Copyright 2024 jack@pngu.org
// SPDX-License-Identifier: MIT/X
#include <X11/Xft/Xft.h>
#include <hb-ft.h>
#include <hb.h>
#include <stdio.h>
#include <stdlib.h>

#include "st.h"

void hbtransformsegment(XftFont *xfont, const Glyph *string,
                        hb_codepoint_t *codepoints, int start, int length);
hb_font_t *hbfindfont(XftFont *match);

typedef struct {
  XftFont *match;
  hb_font_t *font;
} HbFontMatch;

static int hbfontslen = 0;
static HbFontMatch *hbfontcache = NULL;

void hbunloadfonts() {
  for (int i = 0; i < hbfontslen; i++) {
    hb_font_destroy(hbfontcache[i].font);
    XftUnlockFace(hbfontcache[i].match);
  }

  if (hbfontcache != NULL) {
    free(hbfontcache);
    hbfontcache = NULL;
  }
  hbfontslen = 0;
}

hb_font_t *hbfindfont(XftFont *match) {
  for (int i = 0; i < hbfontslen; i++) {
    if (hbfontcache[i].match == match)
      return hbfontcache[i].font;
  }

  /* Font not found in cache, caching it now. */
  hbfontcache = realloc(hbfontcache, sizeof(HbFontMatch) * (hbfontslen + 1));
  FT_Face face = XftLockFace(match);
  hb_font_t *font = hb_ft_font_create(face, NULL);
  if (font == NULL)
    die("Failed to load Harfbuzz font.");

  hbfontcache[hbfontslen].match = match;
  hbfontcache[hbfontslen].font = font;
  hbfontslen += 1;

  return font;
}

void hbtransform(XftGlyphFontSpec *specs, const Glyph *glyphs, size_t len,
                 int x, int y) {
  int start = 0, length = 1, gstart = 0;
  hb_codepoint_t *codepoints = calloc(len, sizeof(hb_codepoint_t));

  for (int idx = 1, specidx = 1; idx < len; idx++) {
    if (glyphs[idx].mode & ATTR_WDUMMY) {
      length += 1;
      continue;
    }

    if (specs[specidx].font != specs[start].font ||
        ATTRCMP(glyphs[gstart], glyphs[idx]) ||
        selected(x + idx, y) != selected(x + gstart, y)) {
      hbtransformsegment(specs[start].font, glyphs, codepoints, gstart, length);

      /* Reset the sequence. */
      length = 1;
      start = specidx;
      gstart = idx;
    } else {
      length += 1;
    }

    specidx++;
  }

  /* EOL. */
  hbtransformsegment(specs[start].font, glyphs, codepoints, gstart, length);

  /* Apply the transformation to glyph specs. */
  for (int i = 0, specidx = 0; i < len; i++) {
    if (glyphs[i].mode & ATTR_WDUMMY)
      continue;
    if (glyphs[i].mode & ATTR_BOXDRAW) {
      specidx++;
      continue;
    }

    if (codepoints[i] != specs[specidx].glyph)
      ((Glyph *)glyphs)[i].mode |= ATTR_LIGA;

    specs[specidx++].glyph = codepoints[i];
  }

  free(codepoints);
}

void hbtransformsegment(XftFont *xfont, const Glyph *string,
                        hb_codepoint_t *codepoints, int start, int length) {
  hb_font_t *font = hbfindfont(xfont);
  if (font == NULL)
    return;

  Rune rune;
  ushort mode = USHRT_MAX;
  hb_buffer_t *buffer = hb_buffer_create();
  hb_buffer_set_direction(buffer, HB_DIRECTION_LTR);

  /* Fill buffer with codepoints. */
  for (int i = start; i < (start + length); i++) {
    rune = string[i].u;
    mode = string[i].mode;
    if (mode & ATTR_WDUMMY)
      rune = 0x0020;
    hb_buffer_add_codepoints(buffer, &rune, 1, 0, 1);
  }

  /* Shape the segment. */
  hb_shape(font, buffer, NULL, 0);

  /* Get new glyph info. */
  hb_glyph_info_t *info = hb_buffer_get_glyph_infos(buffer, NULL);

  /* Write new codepoints. */
  for (int i = 0; i < length; i++) {
    hb_codepoint_t gid = info[i].codepoint;
    codepoints[start + i] = gid;
  }

  /* Cleanup. */
  hb_buffer_destroy(buffer);
}