I want to render the text as this:

But this is what I got:

here’s the full code but for the sake of conciseness I also wrote a small demo in c:

#include "freetype2/ft2build.h"
#include "harfbuzz/hb-ft.h"
#include "hb.h"
#include <stdio.h>
#include FT_FREETYPE_H

int main() {
  FT_Library library;
  FT_Init_FreeType(&library);

  FT_Face face;
  FT_New_Face(library, "./LXGWWenKaiLite-Regular.ttf", 0, &face);

  FT_Set_Char_Size(face, 0, 1000, 0, 0);

  hb_font_t *font = hb_ft_font_create(face, NULL);
  hb_ft_font_set_funcs(font);

  hb_buffer_t *buf = hb_buffer_create();

  hb_buffer_add_utf8(buf, "你好——“我说”", -1, 0, -1);
  hb_buffer_guess_segment_properties(buf);
  hb_shape(font, buf, NULL, 0);
  unsigned int glyph_count;
  hb_glyph_info_t *glyph_info = hb_buffer_get_glyph_infos(buf, &glyph_count);
  hb_glyph_position_t *glyph_pos =
      hb_buffer_get_glyph_positions(buf, &glyph_count);

  hb_position_t cursor_x = 0;
  hb_position_t cursor_y = 0;
  for (unsigned int i = 0; i < glyph_count; i++) {
    hb_codepoint_t glyphid = glyph_info[i].codepoint;
    hb_position_t x_offset = glyph_pos[i].x_offset;
    hb_position_t y_offset = glyph_pos[i].y_offset;
    hb_position_t x_advance = glyph_pos[i].x_advance;
    hb_position_t y_advance = glyph_pos[i].y_advance;
    printf("offset: (%d, %d), advance: (%d, %d)n", x_offset, y_offset,
           x_advance, y_advance);
    /* draw_glyph(glyphid, cursor_x + x_offset, cursor_y + y_offset); */

    cursor_x += x_advance;
    cursor_y += y_advance;
  }
}

And I got this:

offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (350, 0)
offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (1000, 0)
offset: (0, 0), advance: (350, 0)

Which is not what I want as offset is always 0, but in the string “你好——“我说””, I expect the “——” to be centered, which obviously isn’t here.

Is it I’m getting something wrong or that harfbuzz doesn’t solve the bearing y for me?