src/lua/renderer/lua_font.cpp

#ifdef WITH_RIVE_SCRIPTING
#include "lua.h"
#include "lualib.h"
#include "rive/lua/rive_lua_libs.hpp"
#ifdef WITH_RIVE_TEXT
#include "rive/lua/scripted_text.hpp"
#include "rive/text/font_hb.hpp"
#endif

#include <vector>

using namespace rive;

// OpenType tags cross as their four letter names.
static uint32_t tagFromString(lua_State* L, int idx)
{
  size_t length;
  const char* name = luaL_checklstring(L, idx, &length);
  if (length != 4)
  {
    luaL_error(L, "'%s' is not a four letter tag", name);
  }
  return ((uint32_t)(uint8_t)name[0] << 24) |
         ((uint32_t)(uint8_t)name[1] << 16) |
         ((uint32_t)(uint8_t)name[2] << 8) | (uint32_t)(uint8_t)name[3];
}

static void pushTag(lua_State* L, uint32_t tag)
{
  char name[4] =
      {(char)(tag >> 24), (char)(tag >> 16), (char)(tag >> 8), (char)tag};
  lua_pushlstring(L, name, 4);
}

static Font* checkFont(lua_State* L, int idx)
{
  Font* font = lua_torive<ScriptedFont>(L, idx)->font.get();
  if (font == nullptr)
  {
    luaL_error(L, "Font is empty.");
  }
  return font;
}

static void font_direct_ascent(void* udata, void* result)
{
  Font* font = ((ScriptedFont*)udata)->font.get();
  lua_userdatadirectfield_setnumber(
      result,
      font ? font->lineMetrics().ascent : 0.0);
}

static void font_direct_descent(void* udata, void* result)
{
  Font* font = ((ScriptedFont*)udata)->font.get();
  lua_userdatadirectfield_setnumber(
      result,
      font ? font->lineMetrics().descent : 0.0);
}

static int font_index(lua_State* L)
{
  int atom;
  const char* key = lua_tostringatom(L, 2, &atom);
  if (!key)
  {
    luaL_typeerrorL(L, 2, lua_typename(L, LUA_TSTRING));
  }
  Font* font = checkFont(L, 1);
  switch (atom)
  {
    case (int)LuaAtoms::ascent:
      lua_pushnumber(L, font->lineMetrics().ascent);
      return 1;
    case (int)LuaAtoms::descent:
      lua_pushnumber(L, font->lineMetrics().descent);
      return 1;
    case (int)LuaAtoms::capHeight:
      lua_pushnumber(L, font->lineMetrics().capHeight);
      return 1;
    case (int)LuaAtoms::xHeight:
      lua_pushnumber(L, font->lineMetrics().xHeight);
      return 1;
    case (int)LuaAtoms::weight:
      lua_pushnumber(L, font->getWeight());
      return 1;
    case (int)LuaAtoms::isItalic:
      lua_pushboolean(L, font->isItalic());
      return 1;
    case (int)LuaAtoms::axes:
    {
      uint16_t count = font->getAxisCount();
      lua_createtable(L, count, 0);
      for (uint16_t i = 0; i < count; i++)
      {
        Font::Axis axis = font->getAxis(i);
        lua_createtable(L, 0, 4);
        pushTag(L, axis.tag);
        lua_setfield(L, -2, "tag");
        lua_pushnumber(L, axis.min);
        lua_setfield(L, -2, "min");
        lua_pushnumber(L, axis.def);
        lua_setfield(L, -2, "default");
        lua_pushnumber(L, axis.max);
        lua_setfield(L, -2, "max");
        lua_rawseti(L, -2, i + 1);
      }
      return 1;
    }
    case (int)LuaAtoms::features:
    {
      SimpleArray<uint32_t> features = font->features();
      lua_createtable(L, (int)features.size(), 0);
      for (size_t i = 0; i < features.size(); i++)
      {
        pushTag(L, features[i]);
        lua_rawseti(L, -2, (int)i + 1);
      }
      return 1;
    }
  }
  luaL_error(L, "'%s' is not a valid index of %s", key, ScriptedFont::luaName);
  return 0;
}

// Reads { tag = value } pairs into coords or features.
template <typename T, typename Value>
static void readTagTable(lua_State* L, int idx, std::vector<T>& out)
{
  if (lua_isnoneornil(L, idx))
  {
    return;
  }
  luaL_checktype(L, idx, LUA_TTABLE);
  lua_pushnil(L);
  while (lua_next(L, idx))
  {
    // Converting a numeric key in place would break the traversal.
    if (lua_type(L, -2) != LUA_TSTRING)
    {
      luaL_error(L, "font tags are four letter strings");
    }
    out.push_back({tagFromString(L, -2), (Value)luaL_checknumber(L, -1)});
    lua_pop(L, 1);
  }
}

static int font_namecall(lua_State* L)
{
  int atom;
  const char* str = lua_namecallatom(L, &atom);
  Font* font = checkFont(L, 1);
  switch (atom)
  {
    case (int)LuaAtoms::lineHeight:
    {
      float size = (float)luaL_checknumber(L, 2);
      lua_pushnumber(L, font->descent(size) - font->ascent(size));
      return 1;
    }
    case (int)LuaAtoms::hasGlyph:
      lua_pushboolean(L, font->hasGlyph((Unichar)luaL_checkunsigned(L, 2)));
      return 1;
    case (int)LuaAtoms::axisValue:
      lua_pushnumber(L, font->getAxisValue(tagFromString(L, 2)));
      return 1;
    case (int)LuaAtoms::withOptions:
    {
      std::vector<Font::Coord> coords;
      std::vector<Font::Feature> features;
      readTagTable<Font::Coord, float>(L, 2, coords);
      readTagTable<Font::Feature, uint32_t>(L, 3, features);
      lua_pushfont(L, font->withOptions(coords, features));
      return 1;
    }
#ifdef WITH_RIVE_TEXT
    case (int)LuaAtoms::glyphPath:
    {
      RawPath path = RawText::glyphPath(
          *font,
          (GlyphID)luaL_checkunsigned(L, 2));
      lua_newrive<ScriptedPath>(L, &path);
      return 1;
    }
#endif
  }
  luaL_error(L, "%s is not a valid method of %s", str, ScriptedFont::luaName);
  return 0;
}

#ifdef WITH_RIVE_TEXT
static int font_decode(lua_State* L)
{
  size_t length;
  void* bytes = luaL_checkbuffer(L, 1, &length);
  rcp<Font> font = HBFont::Decode(
      Span<const uint8_t>((const uint8_t*)bytes, length));
  if (font == nullptr)
  {
    lua_pushnil(L);
    return 1;
  }
  lua_pushfont(L, std::move(font));
  return 1;
}
#endif

static const luaL_Reg fontStaticMethods[] = {
#ifdef WITH_RIVE_TEXT
    {"decode", font_decode},
#endif
    {NULL, NULL},
};

int luaopen_rive_font(lua_State* L)
{
  luaL_register(L, ScriptedFont::luaName, fontStaticMethods);
  lua_register_rive_type<ScriptedFont>(L, font_index, font_namecall);

  lua_registeruserdatadirectfieldget(
      L,
      ScriptedFont::luaTag,
      "ascent",
      font_direct_ascent);
  lua_registeruserdatadirectfieldget(
      L,
      ScriptedFont::luaTag,
      "descent",
      font_direct_descent);
  return 1;
}
#endif