[HarfBuzz] I got hb/ft working but I don't know how

[Eduardo Castineyra]

Hi,

I just coded my first working Windows example with harfbuzz (code 
attached). I got my first thai characters to be shaped into glyphs (at 
least I got the same output as hb-shape). But I don't really feel like I 
understood anything:

1) What is a blob and how come I didn't need to know what it is?

2) I created a hb_ft_font and passed it to the shaper but, shouldn't I 
also call hb_ft_font_set_funcs in order to use hb-ft as font instance?

3) How does harfbuzz manage to get the GSUB/GPOS tables of the fonts if 
everything I provided was a FT_Face? I don't see anything related to 
those tables in hb-ft, and AFAIK FT2 does not provide tools to extract 
those tables. Is it opening the font file by itself?

4) What is get_ft_library for? Should I be calling it instead of 
FT_Init_FreeType?

Thanks!
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#include <string.h>
#include <ft2build.h>
#include FT_FREETYPE_H
#include <hb.h>
#include <assert.h>
#include <hb-ft.h>

#define MAX_CHARS 2048

int loadUcsFile(char* filename, uint16_t* buf){
	FILE* fp;
	fp = fopen (filename, "r");
	int count = fread(buf, sizeof(uint16_t), MAX_CHARS, fp);
	buf[count] = (uint16_t)0;
	fclose(fp);
	return count;
	}

void loadFTFace(char* filename, FT_Face& ft_face){
	FT_Library ft_library;
    assert(!FT_Init_FreeType(&ft_library));

    /* Load our fonts */
	assert(!FT_New_Face(ft_library, "C:/Windows/fonts/leelawad.ttf", 0, &ft_face));
    assert(!FT_Set_Char_Size(ft_face, 0, 50*64, 72, 72 ));
	FT_Set_Charmap(ft_face, 0);
	//FT_Done_FreeType(ft_library);
	}

void printGlyphs(hb_glyph_info_t *glyph_info, 
				 hb_glyph_position_t *glyph_pos,
				 unsigned int         glyph_count){
	for (int i = 0; i < glyph_count; i++){
		printf("[%4x] Adv(%4d, %4d) Ofs(%4d, %4d)\n", glyph_info[i].codepoint, 
												 glyph_pos[i].x_advance,
												 glyph_pos[i].y_advance,
												 glyph_pos[i].x_offset,
												 glyph_pos[i].y_offset);
		}
	}

int main (int argc, char **argv){
	uint16_t buf[MAX_CHARS];
	int count = loadUcsFile("line.txt", buf);
    FT_Face ft_face;
	hb_font_t *hb_ft_font;

	loadFTFace("C:/Windows/fonts/leelawad.ttf", ft_face);
	hb_ft_font = hb_ft_font_create(ft_face, NULL);
	 
	hb_buffer_t *buffer = hb_buffer_create ();	
	hb_buffer_set_direction(buffer, HB_DIRECTION_LTR); 
	hb_buffer_set_script(buffer, HB_SCRIPT_THAI);
	hb_buffer_set_language(buffer, hb_language_from_string("th", strlen("th"))); // see hb-ot-tag.cc
	// hb_buffer_guess_segment_properties(buffer);

	hb_buffer_add_utf16(buffer, buf, count, 0, count);
	hb_shape(hb_ft_font, buffer, NULL, 0);

    unsigned int         glyph_count;
    hb_glyph_info_t     *glyph_info   = hb_buffer_get_glyph_infos(buffer, &glyph_count);
    hb_glyph_position_t *glyph_pos    = hb_buffer_get_glyph_positions(buffer, &glyph_count);

	printGlyphs(glyph_info, glyph_pos, glyph_count);

	hb_buffer_destroy (buffer);
	}