add PSO GC snapshot decoder

README.md

@@ -394,6 +394,7 @@ newserv has many CLI options, which can be used to access functionality other th
 * Encrypt or decrypt data using Episode 3's trivial scheme (`encrypt-trivial-data`, `decrypt-trivial-data`)
 * Encrypt or decrypt data using the Challenge Mode text algorithm (`encrypt-challenge-data`, `decrypt-challenge-data`)
 * Encrypt or decrypt PSO GC save data (.gci files) (`encrypt-gci-save`, `decrypt-gci-save`)
+* Convert a PSO GC or Episode 3 snapshot file to a BMP image (`decode-gci-snapshot`)
 * Find the likely round1 or round2 seed for a corrupt save file (`salvage-gci`)
 * Run a brute-force search for a decryption seed (`find-decryption-seed`)
 * Decode Shift-JIS text to UTF-16 (`decode-sjis`)

src/Main.cc

@@ -273,6 +273,7 @@ enum class Behavior {
   DECRYPT_CHALLENGE_DATA,
   ENCRYPT_GCI_SAVE,
   DECRYPT_GCI_SAVE,
+  DECODE_GCI_SNAPSHOT,
   FIND_DECRYPTION_SEED,
   SALVAGE_GCI,
   DECODE_QUEST_FILE,
@@ -314,6 +315,7 @@ static bool behavior_takes_input_filename(Behavior b) {
       (b == Behavior::ENCRYPT_CHALLENGE_DATA) ||
       (b == Behavior::DECRYPT_CHALLENGE_DATA) ||
       (b == Behavior::DECRYPT_GCI_SAVE) ||
+      (b == Behavior::DECODE_GCI_SNAPSHOT) ||
       (b == Behavior::SALVAGE_GCI) ||
       (b == Behavior::ENCRYPT_GCI_SAVE) ||
       (b == Behavior::DECODE_QUEST_FILE) ||
@@ -347,6 +349,7 @@ static bool behavior_takes_output_filename(Behavior b) {
       (b == Behavior::DECRYPT_CHALLENGE_DATA) ||
       (b == Behavior::DECRYPT_GCI_SAVE) ||
       (b == Behavior::ENCRYPT_GCI_SAVE) ||
+      (b == Behavior::DECODE_GCI_SNAPSHOT) ||
       (b == Behavior::ENCODE_QST) ||
       (b == Behavior::DISASSEMBLE_QUEST_SCRIPT) ||
       (b == Behavior::CONVERT_ITEMRT_REL_TO_JSON) ||
@@ -520,6 +523,8 @@ int main(int argc, char** argv) {
           behavior = Behavior::DECRYPT_GCI_SAVE;
         } else if (!strcmp(argv[x], "encrypt-gci-save")) {
           behavior = Behavior::ENCRYPT_GCI_SAVE;
+        } else if (!strcmp(argv[x], "decode-gci-snapshot")) {
+          behavior = Behavior::DECODE_GCI_SNAPSHOT;
         } else if (!strcmp(argv[x], "find-decryption-seed")) {
           behavior = Behavior::FIND_DECRYPTION_SEED;
         } else if (!strcmp(argv[x], "salvage-gci")) {
@@ -639,6 +644,8 @@ int main(int argc, char** argv) {
         } else {
           filename += ".dec";
         }
+      } else if (behavior == Behavior::DECODE_GCI_SNAPSHOT) {
+        filename += ".bmp";
       } else if (behavior == Behavior::DISASSEMBLE_QUEST_SCRIPT) {
         filename += ".txt";
       } else if (behavior == Behavior::CONVERT_ITEMRT_REL_TO_JSON) {
@@ -968,6 +975,26 @@ int main(int argc, char** argv) {
       break;
     }
 
+    case Behavior::DECODE_GCI_SNAPSHOT: {
+      auto data = read_input_data();
+      StringReader r(data);
+      const auto& header = r.get<PSOGCIFileHeader>();
+      try {
+        header.check();
+      } catch (const exception& e) {
+        log_warning("File header failed validation (%s)", e.what());
+      }
+      const auto& file = r.get<PSOGCSnapshotFile>();
+      if (!file.checksum_correct()) {
+        log_warning("File internal checksum is incorrect");
+      }
+
+      auto img = file.decode_image();
+      string saved = img.save(Image::Format::WINDOWS_BITMAP);
+      write_output_data(saved.data(), saved.size());
+      break;
+    }
+
     case Behavior::SALVAGE_GCI: {
       uint64_t likely_round1_seed = 0xFFFFFFFFFFFFFFFF;
       if (system_filename) {

src/SaveFileFormats.cc

@@ -115,3 +115,42 @@ string decrypt_gci_fixed_size_file_data_section_for_salvage(
 
   return decrypted;
 }
+
+bool PSOGCSnapshotFile::checksum_correct() const {
+  uint32_t crc = crc32("\0\0\0\0", 4);
+  crc = crc32(&this->width, sizeof(*this) - sizeof(this->checksum), crc);
+  return (crc == this->checksum);
+}
+
+static uint32_t decode_rgb565(uint16_t c) {
+  // Input:                    rrrrrggg gggbbbbb
+  // Output: rrrrrrrr gggggggg bbbbbbbb aaaaaaaa
+  return ((c << 16) & 0xF8000000) | ((c << 11) & 0x07000000) | // R
+      ((c << 13) & 0x00FC0000) | ((c << 7) & 0x00030000) | // G
+      ((c << 11) & 0x0000F800) | ((c << 6) & 0x00000700) | // B
+      0x000000FF; // A
+}
+
+Image PSOGCSnapshotFile::decode_image() const {
+  if (this->width != 256) {
+    throw runtime_error("width is incorrect");
+  }
+  if (this->height != 192) {
+    throw runtime_error("height is incorrect");
+  }
+
+  // 4x4 blocks of pixels
+  Image ret(this->width, this->height, false);
+  size_t offset = 0;
+  for (size_t y = 0; y < this->height; y += 4) {
+    for (size_t x = 0; x < this->width; x += 4) {
+      for (size_t yy = 0; yy < 4; yy++) {
+        for (size_t xx = 0; xx < 4; xx++) {
+          uint32_t color = decode_rgb565(this->pixels[offset++]);
+          ret.write_pixel(x + xx, y + yy, color);
+        }
+      }
+    }
+  }
+  return ret;
+}

src/SaveFileFormats.hh

@@ -5,6 +5,7 @@
 #include <algorithm>
 #include <phosg/Encoding.hh>
 #include <phosg/Hash.hh>
+#include <phosg/Image.hh>
 #include <phosg/Random.hh>
 #include <phosg/Strings.hh>
 #include <string>
@@ -279,6 +280,23 @@ struct PSOGCGuildCardFile {
   /* E28C */
 } __attribute__((packed));
 
+struct PSOGCSnapshotFile {
+  /* 00000 */ be_uint32_t checksum;
+  /* 00004 */ be_uint16_t width;
+  /* 00006 */ be_uint16_t height;
+  /* 00008 */ parray<be_uint16_t, 0xC000> pixels;
+  /* 18008 */ uint8_t unknown_a1; // Always 0x18?
+  /* 18009 */ uint8_t unknown_a2;
+  /* 1800A */ be_int16_t max_players;
+  /* 1800C */ parray<be_uint32_t, 12> players_present;
+  /* 1803C */ parray<be_uint32_t, 12> player_levels;
+  /* 1806C */ parray<ptext<char, 0x18>, 12> player_names;
+  /* 1818C */
+
+  bool checksum_correct() const;
+  Image decode_image() const;
+} __attribute__((packed));
+
 template <bool IsBigEndian>
 std::string decrypt_gci_or_vms_v2_data_section(
     const void* data_section, size_t size, uint32_t round1_seed, size_t max_decrypt_bytes = 0) {