path: root/src/gui/font.c

// FreeType and HarfBuzz wrapper for gui.zig. The policy intentionally follows
// Ghostty's FreeType backend: native hinting enabled, the auto-hinter available
// as a fallback, and the light target for shape-preserving grayscale text.
// HarfBuzz only picks glyphs (liga, calt); the grid, not the font's advances,
// places them.
#include "font.h"
#include <freetype-zig.h>
#include <freetype/ftbitmap.h>
#include <freetype/ftmodapi.h>
#include <hb-ft.h>
#include <hb-ot.h>
#include <hb.h>

#include <string.h>

struct UIFont {
  // FreeType allocates through ui_malloc and friends: the library holds a
  // pointer to this for its lifetime, which the UIFont outlives.
  struct FT_MemoryRec_ memory;
  FT_Library library;
  FT_Face face;
  FT_F26Dot6 size;
  // The charmap's answer for ASCII, which is most of every screen: a word the
  // renderer has not seen before looks up each of its cells.
  uint32_t ascii[128];
  // HarfBuzz state, made by the first ui_font_substitutes question (most
  // fallback faces are never asked).
  hb_font_t *hb;
  hb_buffer_t *buffer;
  FT_F26Dot6 hb_size;
  // Every glyph a lookup of a ligature feature could replace. Nothing else
  // can change a glyph, so a cell outside it is its nominal glyph without
  // shaping: every cell, in a font without ligatures.
  hb_set_t *substitutes;
  // ui_font_shape's per-cell scratch, grown to the longest run seen
  uint32_t *own;
  uint8_t *state;
  int32_t scratch;
};

static FT_F26Dot6 size_26_6(float px) {
  if (px < 1.0f)
    px = 1.0f;
  return (FT_F26Dot6)(px * 64.0f + 0.5f);
}

static int set_size(UIFont *f, float px) {
  const FT_F26Dot6 size = size_26_6(px);
  if (f->size == size)
    return 1;
  if (FT_Set_Char_Size(f->face, 0, size, 72, 72) != 0)
    return 0;
  f->size = size;
  return 1;
}

static int ceil_26_6(FT_Pos value) { return (int)((value + 63) >> 6); }

static FT_Int32 load_flags(void) {
  // Hinting is on because FT_LOAD_NO_HINTING is absent. Likewise, leaving
  // FT_LOAD_NO_AUTOHINT absent lets FreeType fall back to its auto-hinter
  // when the face has no native instructions. This is Ghostty's default.
  return FT_LOAD_DEFAULT | FT_LOAD_TARGET_LIGHT;
}

static void *ft_alloc(FT_Memory memory, long size) {
  (void)memory;
  return ui_malloc((size_t)size);
}

static void ft_free(FT_Memory memory, void *block) {
  (void)memory;
  ui_free(block);
}

static void *ft_realloc(FT_Memory memory, long cur_size, long new_size,
                        void *block) {
  (void)memory;
  (void)cur_size;
  return ui_realloc(block, (size_t)new_size);
}

UIFont *ui_font_new(const uint8_t *data, int32_t len) {
  if (!data || len <= 0)
    return NULL;

  UIFont *f = (UIFont *)ui_calloc(1, sizeof(UIFont));
  if (!f)
    return NULL;
  // FT_Init_FreeType is exactly FT_New_Library over FT_New_Memory's malloc
  // manager, then the default modules and properties: the same, over ours.
  f->memory = (struct FT_MemoryRec_){NULL, ft_alloc, ft_free, ft_realloc};
  if (FT_New_Library(&f->memory, &f->library) != 0) {
    ui_free(f);
    return NULL;
  }
  FT_Add_Default_Modules(f->library);
  FT_Set_Default_Properties(f->library);
  if (FT_New_Memory_Face(f->library, data, (FT_Long)len, 0, &f->face) != 0) {
    FT_Done_Library(f->library);
    ui_free(f);
    return NULL;
  }
  // Some symbol fonts do not expose a Unicode charmap. FreeType already
  // selects a usable default for those, so failure here is non-fatal.
  (void)FT_Select_Charmap(f->face, FT_ENCODING_UNICODE);
  for (uint32_t cp = 0; cp < 128; cp++)
    f->ascii[cp] = FT_Get_Char_Index(f->face, cp);
  return f;
}

// HarfBuzz reads this same face (and its charmap) through FreeType, so shaping
// and rasterizing agree on glyph ids. None of these calls returns NULL: a
// failure is an inert empty object, and shaping then yields nominal glyphs.
static void start_harfbuzz(UIFont *f) {
  f->hb = hb_ft_font_create_referenced(f->face);
  f->buffer = hb_buffer_create();
  f->substitutes = hb_set_create();
  static const hb_tag_t features[] = {
      HB_TAG('l', 'i', 'g', 'a'), HB_TAG('c', 'a', 'l', 't'),
      HB_TAG('c', 'l', 'i', 'g'), HB_TAG('r', 'l', 'i', 'g'),
      HB_TAG('r', 'c', 'l', 't'), HB_TAG_NONE};
  hb_face_t *face = hb_font_get_face(f->hb);
  hb_set_t *lookups = hb_set_create();
  hb_ot_layout_collect_lookups(face, HB_OT_TAG_GSUB, NULL, NULL, features,
                               lookups);
  hb_codepoint_t lookup = HB_SET_VALUE_INVALID;
  while (hb_set_next(lookups, &lookup))
    hb_ot_layout_lookup_collect_glyphs(face, HB_OT_TAG_GSUB, lookup, NULL,
                                       f->substitutes, NULL, NULL);
  hb_set_destroy(lookups);
}

const char *ui_font_name(UIFont *f) {
  if (!f || !f->face)
    return NULL;
  const char *postscript = FT_Get_Postscript_Name(f->face);
  if (postscript && postscript[0])
    return postscript;
  if (f->face->family_name && f->face->family_name[0])
    return f->face->family_name;
  return NULL;
}

uint32_t ui_font_glyph(UIFont *f, int32_t cp) {
  if (!f || cp < 0)
    return 0;
  if (cp < 128)
    return f->ascii[cp];
  return FT_Get_Char_Index(f->face, (FT_ULong)(uint32_t)cp);
}

void ui_font_free(UIFont *f) {
  if (!f)
    return;
  // The HarfBuzz font holds a reference on the face: release it first. (All
  // three accept NULL, a face that never shaped.)
  hb_set_destroy(f->substitutes);
  hb_buffer_destroy(f->buffer);
  hb_font_destroy(f->hb);
  if (f->face)
    FT_Done_Face(f->face);
  if (f->library)
    FT_Done_Library(f->library);
  ui_free(f->own);
  ui_free(f->state);
  ui_free(f);
}

void ui_font_prime(UIFont *f) {
  if (!f)
    return;
  hb_font_destroy(hb_ft_font_create_referenced(f->face));
  hb_buffer_t *buffer = hb_buffer_create();
  hb_buffer_add_utf8(buffer, "a", 1, 0, 1);
  hb_buffer_guess_segment_properties(buffer);
  hb_buffer_destroy(buffer);
}

void ui_font_cell_metrics(UIFont *f, float px, int32_t *cell_w, int32_t *cell_h,
                          int32_t *ascent) {
  if (!f || !cell_w || !cell_h || !ascent || !set_size(f, px)) {
    if (cell_w)
      *cell_w = 1;
    if (cell_h)
      *cell_h = 1;
    if (ascent)
      *ascent = 1;
    return;
  }

  const FT_Size_Metrics metrics = f->face->size->metrics;
  const int asc = ceil_26_6(metrics.ascender);
  const int desc = ceil_26_6(-metrics.descender);
  int height = ceil_26_6(metrics.height);
  if (height < asc + desc)
    height = asc + desc;

  int width = ceil_26_6(metrics.max_advance);
  const FT_UInt m = FT_Get_Char_Index(f->face, 'M');
  if (FT_Load_Glyph(f->face, m, load_flags()) == 0) {
    const int advance = ceil_26_6(f->face->glyph->advance.x);
    if (advance > 0)
      width = advance;
  }

  *cell_w = width > 0 ? width : 1;
  *cell_h = height > 0 ? height : 1;
  *ascent = asc > 0 ? asc : 1;
}

static int raster(UIFont *f, float px, uint32_t glyph_index, int bold,
                  uint8_t *out, int32_t stride, int32_t width, int32_t height,
                  int32_t cell_x, int32_t cell_w, int32_t ascent,
                  int centered) {
  if (!f || !out || stride < width || width <= 0 || height <= 0)
    return 0;
  for (int y = 0; y < height; y++)
    memset(out + (size_t)y * (size_t)stride, 0, (size_t)width);
  if (!set_size(f, px))
    return 0;

  if (FT_Load_Glyph(f->face, glyph_index, load_flags()) != 0)
    return 0;
  if (bold) {
    // Synthetic bold thickens the hinted outline before it is rendered, so
    // the wider stems are rasterized as one shape and keep hinted edges; the
    // advance is untouched, as the cell grid requires. Strength is Ghostty's
    // heuristic: 1/32 of the line height in 26.6, rounded up (one pixel at a
    // 32 px line). A bitmap strike has no outline: widen it by one whole pixel,
    // the classic overstrike, which keeps its pixels sharp.
    FT_GlyphSlot slot = f->face->glyph;
    if (slot->format == FT_GLYPH_FORMAT_OUTLINE) {
      const FT_Pos height = f->face->size->metrics.height;
      FT_Outline_Embolden(&slot->outline, (height + 31) / 32);
    } else if (slot->format == FT_GLYPH_FORMAT_BITMAP &&
               FT_GlyphSlot_Own_Bitmap(slot) == 0) {
      FT_Bitmap_Embolden(f->library, &slot->bitmap, 64, 0);
    }
  }
  if (FT_Render_Glyph(f->face->glyph, FT_RENDER_MODE_NORMAL) != 0)
    return 0;

  const FT_GlyphSlot glyph = f->face->glyph;
  const FT_Bitmap *bitmap = &glyph->bitmap;
  if (!bitmap->buffer || bitmap->width == 0 || bitmap->rows == 0)
    return 0;

  const int advance = ceil_26_6(glyph->advance.x);
  // Fallbacks may be proportional. Center their advance in the primary face's
  // fixed cell, exactly as Ghostty centers a narrower fallback face.
  const int gx = centered
                     ? (width - (int)bitmap->width) / 2
                     : cell_x + glyph->bitmap_left + (cell_w - advance) / 2;
  const int gy =
      centered ? (height - (int)bitmap->rows) / 2 : ascent - glyph->bitmap_top;
  const int pitch = bitmap->pitch;
  const int row_bytes = pitch < 0 ? -pitch : pitch;

  for (unsigned int y = 0; y < bitmap->rows; y++) {
    const int dy = gy + (int)y;
    if (dy < 0 || dy >= height)
      continue;
    const unsigned int source_y = pitch < 0 ? bitmap->rows - 1 - y : y;
    const uint8_t *src = bitmap->buffer + (size_t)source_y * (size_t)row_bytes;

    for (unsigned int x = 0; x < bitmap->width; x++) {
      const int dx = gx + (int)x;
      if (dx < 0 || dx >= width)
        continue;

      uint8_t coverage;
      if (bitmap->pixel_mode == FT_PIXEL_MODE_MONO) {
        coverage = (src[x >> 3] & (0x80u >> (x & 7))) ? 255 : 0;
      } else if (bitmap->pixel_mode == FT_PIXEL_MODE_GRAY) {
        coverage = src[x];
        if (bitmap->num_grays > 1 && bitmap->num_grays != 256)
          coverage = (uint8_t)((unsigned int)coverage * 255u /
                               (bitmap->num_grays - 1u));
      } else {
        continue;
      }
      out[(size_t)dy * (size_t)stride + (size_t)dx] = coverage;
    }
  }
  return 1;
}

int ui_font_raster(UIFont *f, float px, uint32_t glyph, int bold, uint8_t *out,
                   int32_t stride, int32_t width, int32_t height,
                   int32_t cell_x, int32_t cell_w, int32_t ascent) {
  return raster(f, px, glyph, bold, out, stride, width, height, cell_x, cell_w,
                ascent, 0);
}

int ui_font_raster_centered(UIFont *f, float px, uint32_t glyph, int bold,
                            uint8_t *out, int32_t stride, int32_t width,
                            int32_t height) {
  return raster(f, px, glyph, bold, out, stride, width, height, 0, width, 0, 1);
}

// The horizontal ink of `glyph` placed as ui_font_raster places it in a cell
// `cell` wide (26.6), relative to the cell's left edge. 0 when it has no ink.
static int ink(UIFont *f, uint32_t glyph, FT_Pos cell, FT_Pos *left,
               FT_Pos *right) {
  if (FT_Load_Glyph(f->face, glyph, load_flags()) != 0)
    return 0;
  const FT_GlyphSlot slot = f->face->glyph;
  if (slot->metrics.width <= 0 || slot->metrics.height <= 0)
    return 0;
  const FT_Pos origin =
      (FT_Pos)(((int)(cell >> 6) - ceil_26_6(slot->advance.x)) / 2) * 64;
  *left = origin + slot->metrics.horiBearingX;
  *right = *left + slot->metrics.width;
  return 1;
}

// ui_font_shape's per-cell marks: no glyph of its own, keep the nominal glyph,
// drawn as a slice of another cell's glyph.
#define NONE UINT32_MAX
#define PLAIN 1
#define CLAIMED 2

int ui_font_substitutes(UIFont *f, uint32_t glyph) {
  if (!f)
    return 0;
  if (!f->hb)
    start_harfbuzz(f);
  return hb_set_has(f->substitutes, glyph);
}

// The GSUB features shaping leaves on are the ligature ones; the others
// HarfBuzz would apply (glyph composition, local forms, fractions around
// U+2044, ...) are off, so a cell is either its nominal glyph, as the renderer
// always drew it, or part of a ligature. Positioning is untouched: the grid
// ignores advances and keeps nominal glyphs where marks would move.
static const hb_feature_t shaping_features[] = {
    {HB_TAG('c', 'c', 'm', 'p'), 0, 0, (unsigned int)-1},
    {HB_TAG('l', 'o', 'c', 'l'), 0, 0, (unsigned int)-1},
    {HB_TAG('r', 'v', 'r', 'n'), 0, 0, (unsigned int)-1},
    {HB_TAG('l', 't', 'r', 'a'), 0, 0, (unsigned int)-1},
    {HB_TAG('l', 't', 'r', 'm'), 0, 0, (unsigned int)-1},
    {HB_TAG('r', 'a', 'n', 'd'), 0, 0, (unsigned int)-1},
    {HB_TAG('f', 'r', 'a', 'c'), 0, 0, (unsigned int)-1},
    {HB_TAG('n', 'u', 'm', 'r'), 0, 0, (unsigned int)-1},
    {HB_TAG('d', 'n', 'o', 'm'), 0, 0, (unsigned int)-1},
};

void ui_font_shape(UIFont *f, float px, int32_t cell_w, const uint32_t *cps,
                   int32_t n, UIShapedCell *out) {
  if (!f || !cps || !out || n <= 0)
    return;
  for (int32_t i = 0; i < n; i++)
    out[i] = (UIShapedCell){ui_font_glyph(f, (int32_t)cps[i]), 0, 1, 0};
  if (!f->hb)
    start_harfbuzz(f);
  int substitutable = 0;
  for (int32_t i = 0; i < n && !substitutable; i++)
    substitutable = hb_set_has(f->substitutes, out[i].glyph);
  if (!substitutable || cell_w <= 0 || !set_size(f, px))
    return;
  if (n > f->scratch) {
    uint32_t *own = (uint32_t *)ui_realloc(f->own, (size_t)n * sizeof *own);
    if (!own)
      return;
    f->own = own;
    uint8_t *state = (uint8_t *)ui_realloc(f->state, (size_t)n);
    if (!state)
      return;
    f->state = state;
    f->scratch = n;
  }
  // hb-ft reads the FreeType size when told; positions are only consulted
  // for being nonzero, but a zero scale would hide exactly that.
  if (f->hb_size != f->size) {
    hb_ft_font_changed(f->hb);
    f->hb_size = f->size;
  }
  hb_buffer_clear_contents(f->buffer);
  // One codepoint per cell, so a cluster value IS a cell index.
  hb_buffer_add_codepoints(f->buffer, cps, n, 0, n);
  hb_buffer_set_direction(f->buffer, HB_DIRECTION_LTR);
  hb_buffer_guess_segment_properties(f->buffer);
  hb_shape(f->hb, f->buffer, shaping_features,
           sizeof shaping_features / sizeof shaping_features[0]);
  unsigned int count = 0;
  const hb_glyph_info_t *info = hb_buffer_get_glyph_infos(f->buffer, &count);
  const hb_glyph_position_t *pos =
      hb_buffer_get_glyph_positions(f->buffer, &count);

  // Each cell's own glyph is the one HarfBuzz left in its cluster. A cell a
  // ligature merged into an earlier cluster has NONE. A cluster the grid
  // cannot place (several glyphs, a positioned mark) is PLAIN, and so are the
  // cells merged into it: they keep their nominal glyphs.
  uint32_t *own = f->own;
  uint8_t *state = f->state;
  for (int32_t i = 0; i < n; i++) {
    own[i] = NONE;
    state[i] = 0;
  }
  for (unsigned int k = 0; k < count; k++) {
    const uint32_t cluster = info[k].cluster;
    if (cluster >= (uint32_t)n)
      continue;
    if (own[cluster] != NONE || pos[k].x_offset != 0 || pos[k].y_offset != 0)
      state[cluster] = PLAIN;
    else
      own[cluster] = info[k].codepoint;
  }
  for (int32_t i = 1; i < n; i++)
    if (own[i] == NONE && (state[i - 1] & PLAIN))
      state[i] = PLAIN;

  // A substituted glyph (or one whose cluster swallowed cells) may reach over
  // its neighbours: it claims those that draw nothing of their own, nearest
  // first, and each draws its slice of the one strip. Ink past a cell edge by
  // half a pixel or less is noise.
  const FT_Pos cell = (FT_Pos)cell_w * 64;
  for (int32_t i = 0; i < n; i++) {
    if ((state[i] & (PLAIN | CLAIMED)) || own[i] == NONE)
      continue;
    int32_t merged = 0;
    while (i + 1 + merged < n && own[i + 1 + merged] == NONE &&
           !(state[i + 1 + merged] & PLAIN))
      merged++;
    if (own[i] == out[i].glyph && merged == 0)
      continue;
    FT_Pos left = 0, right = 0;
    if (!ink(f, own[i], cell, &left, &right))
      continue; // a spacer: claimed, never claiming
    int32_t want_left =
        left < -32 ? (int32_t)((-left - 32 + cell - 1) / cell) : 0;
    int32_t want_right = right > cell + 32
                             ? (int32_t)((right - cell - 32 + cell - 1) / cell)
                             : 0;
    if (want_right < merged)
      want_right = merged;
    int32_t lead = 0, trail = 0;
    while (lead < want_left && 1 + lead + trail < UI_MAX_SPAN) {
      const int32_t j = i - lead - 1;
      FT_Pos l, r;
      if (j < 0 || (state[j] & (PLAIN | CLAIMED)) ||
          (own[j] != NONE &&
           (own[j] == out[j].glyph || ink(f, own[j], cell, &l, &r))))
        break;
      lead++;
    }
    while (trail < want_right && 1 + lead + trail < UI_MAX_SPAN) {
      const int32_t j = i + trail + 1;
      FT_Pos l, r;
      if (j >= n || (state[j] & (PLAIN | CLAIMED)) ||
          (own[j] != NONE &&
           (own[j] == out[j].glyph || ink(f, own[j], cell, &l, &r))))
        break;
      trail++;
    }
    for (int32_t j = i - lead; j <= i + trail; j++) {
      out[j] =
          (UIShapedCell){own[i], (uint8_t)lead, (uint8_t)(1 + lead + trail),
                         (uint8_t)(j - (i - lead))};
      state[j] |= CLAIMED;
    }
  }
  // The rest draw their own glyph; a merged cell nothing claimed draws blank.
  const uint32_t space = f->ascii[' '];
  for (int32_t i = 0; i < n; i++) {
    if (state[i] & (PLAIN | CLAIMED))
      continue;
    out[i].glyph = own[i] == NONE ? space : own[i];
  }
}