engine/src/resources/font.cpp

#include "resources/font.h"

#include <string>
#include <stdexcept>

#include <stb_truetype.h>

#include "log.h"
#include "util/files.h"

namespace engine {

Font::Font(const std::string& path) {
  font_buffer_ = util::ReadBinaryFile(path);
  font_info_ = std::make_unique<stbtt_fontinfo>();

  if (stbtt_InitFont(font_info_.get(), font_buffer_->data(), 0) == 0) {
    throw std::runtime_error("Failed to initialise font!");
  }

  LOG_DEBUG("Created font: {}", path);
}

Font::~Font() { LOG_DEBUG("Destroying font..."); }

std::unique_ptr<std::vector<uint8_t>> Font::GetTextBitmap(
    const std::string& text, float height_px, int& width_out, int& height_out) {
  const float sf = stbtt_ScaleForPixelHeight(font_info_.get(), height_px);

  int ascent, descent, line_gap;
  stbtt_GetFontVMetrics(font_info_.get(), &ascent, &descent, &line_gap);

  struct CharacterRenderInfo {
    int advance;  // bitmap advance
    bool isEmpty;
    int xoff, yoff, width, height;
    unsigned char* bitmap;
  };

  std::vector<CharacterRenderInfo> characterRenderInfos{};

  int width = 0;
  for (size_t i = 0; i < text.size(); i++) {
    const int glyph_index = GetGlyphIndex(static_cast<int>(text.at(i)));

    int advanceWidth, leftSideBearing;
    stbtt_GetGlyphHMetrics(font_info_.get(), glyph_index, &advanceWidth,
                           &leftSideBearing);

    if (i == 0 && leftSideBearing < 0) {
      // if the character extends before the current point
      width -= leftSideBearing;
    }
    width += advanceWidth;

    CharacterRenderInfo renderInfo{};

    renderInfo.advance = static_cast<int>(static_cast<float>(advanceWidth) * sf);

    if (stbtt_IsGlyphEmpty(font_info_.get(), glyph_index) == 0) {
      renderInfo.isEmpty = false;
    } else {
      renderInfo.isEmpty = true;
    }

    if (!renderInfo.isEmpty) {
      renderInfo.bitmap = stbtt_GetGlyphBitmap(
          font_info_.get(), sf, sf, glyph_index, &renderInfo.width,
          &renderInfo.height, &renderInfo.xoff, &renderInfo.yoff);
    }

    characterRenderInfos.push_back(renderInfo);
  }

  const size_t bitmap_width = std::ceil(static_cast<float>(width) * sf);
  const size_t bitmap_height =
      std::ceil(static_cast<float>(ascent - descent) * sf);
  auto bitmap =
      std::make_unique<std::vector<uint8_t>>(bitmap_width * bitmap_height * 4);

  for (size_t i = 0; i < bitmap->size() / 4; i++) {
    bitmap->at(i * 4 + 0) = 0x00;
    bitmap->at(i * 4 + 1) = 0x00;
    bitmap->at(i * 4 + 2) = 0x00;
    bitmap->at(i * 4 + 3) = 0x00;
  }

  int top_left_x = 0;
  for (const auto& renderInfo : characterRenderInfos) {
    if (renderInfo.isEmpty == false) {
      top_left_x += renderInfo.xoff;
      const int top_left_y = static_cast<int>(ascent * sf) + renderInfo.yoff;
      const int char_bitmap_width = renderInfo.width;
      const int char_bitmap_height = renderInfo.height;

      // copy the 8bpp char bitmap to the 4bpp output
      for (int y = 0; y < char_bitmap_height; y++) {
        for (int x = 0; x < char_bitmap_width; x++) {
          const int out_index =
              ((bitmap_width * (top_left_y + y)) + (top_left_x + x)) * 4;
          const uint8_t pixel = renderInfo.bitmap[y * char_bitmap_width + x];
          (*bitmap)[out_index + 0] = pixel;
          (*bitmap)[out_index + 1] = pixel;
          (*bitmap)[out_index + 2] = pixel;
          (*bitmap)[out_index + 3] = (pixel == 0x00) ? 0x00 : 0xFF;
        }
      }

      stbtt_FreeBitmap(renderInfo.bitmap, nullptr);
    }

    top_left_x += renderInfo.advance - renderInfo.xoff;
  }

  width_out = bitmap_width;
  height_out = bitmap_height;
  return bitmap;
}

int Font::GetGlyphIndex(int unicode_codepoint) {
  if (unicode_to_glyph_.contains(unicode_codepoint)) {
    return unicode_to_glyph_.at(unicode_codepoint);
  } else {
    const int glyph_index =
        stbtt_FindGlyphIndex(font_info_.get(), unicode_codepoint);
    if (glyph_index == 0) {
      throw std::runtime_error("Glyph not found in font!");
    }
    unicode_to_glyph_.emplace(std::make_pair(unicode_codepoint, glyph_index));
    return glyph_index;
  }
}

}  // namespace engine