add simple text rendering with freetype & harfbuzz

 * <http://www.gnu.org/licenses/>.

 */

#include "text.h"

#include <iostream>

#include <cairo-ft.h>

#include <ft2build.h>

#include FT_FREETYPE_H

#include <freetype/ftadvanc.h>

#include <freetype/ftsnames.h>

#include <freetype/tttables.h>

#include <harfbuzz/hb.h>

#include <harfbuzz/hb-ft.h>

#include <harfbuzz/hb-icu.h>

namespace signaltk {

TextStyle::TextStyle() :

    halign(TextHAlign::LEFT),

    valign(TextVAlign::CENTER),

    font_size(12) {}

void drawText(

    Layer* layer,

    const std::string& text,

    const TextStyle& text_style,

    double x,

    double y,

    const std::string& halign,

    const std::string& valign,

    const std::string& class_name,

    double rotate) {

  // here be dragons

    Layer* layer) {

  auto ctx = layer->ctx;

  auto dpi = layer->dpi;

  auto hb_buf = hb_buffer_create();

  hb_buffer_set_unicode_funcs(hb_buf, hb_icu_get_unicode_funcs());

  hb_buffer_set_direction(hb_buf, HB_DIRECTION_LTR);

  hb_buffer_set_script(hb_buf, HB_SCRIPT_LATIN);

  FT_Library ft_library;

  assert(!FT_Init_FreeType(&ft_library));

  FT_Face ft_face;

  assert(!FT_New_Face(ft_library, "/usr/share/fonts/google-roboto/Roboto-Regular.ttf", 0, &ft_face));

  assert(!FT_Set_Char_Size(ft_face, 0, text_style.font_size * 64, dpi, dpi));

  auto hb_font = hb_ft_font_create(ft_face, NULL);

  auto cairo_face = cairo_ft_font_face_create_for_ft_face(ft_face, 0);

  hb_buffer_add_utf8(hb_buf, text.data(), text.size(), 0, text.size());

  hb_shape(hb_font, hb_buf, NULL, 0);

  unsigned int glyph_count;

  auto hb_glyph_info = hb_buffer_get_glyph_infos(hb_buf, &glyph_count);

  auto hb_glyph_pos = hb_buffer_get_glyph_positions(hb_buf, &glyph_count);

  auto cairo_glyphs = new cairo_glyph_t[glyph_count];

  double g_x = x;

  for (int i = 0; i < glyph_count; ++i) {

    cairo_glyphs[i].index = hb_glyph_info[i].codepoint;

    cairo_glyphs[i].x = g_x + (hb_glyph_pos[i].x_offset / 64.0);

    cairo_glyphs[i].y = y;

    g_x += (hb_glyph_pos[i].x_advance / 64.0);

  }

  cairo_set_source_rgba(ctx, 0.5, 0.5, 0.5, 1.0);

  cairo_set_font_face(ctx, cairo_face);

  cairo_set_font_size(ctx, text_style.font_size);

  cairo_show_glyphs(ctx, cairo_glyphs, glyph_count);

  delete cairo_glyphs;

  hb_buffer_destroy(hb_buf);

}

} // namespace signaltk