Add AI-versus-AI spectator mode and modern GCC fixes

Makefile

@@ -19,7 +19,7 @@ LIBS = -lncurses
 # You shouldn't have to modify anything below this line.
 
 # There's a dynamic format in the object-display routines; suppress the warning
-CFLAGS = $(DEBUG) $(PROFILE) -Wall -Wno-format-security
+CFLAGS = $(DEBUG) $(PROFILE) -Wall -Wno-format-security -fcommon
 
 FILES = \
 	attack.c \
@@ -111,7 +111,7 @@ uninstall:
 
 clean:
 	rm -f *.o TAGS vms-empire
-	rm -f *.6 *.html
+	rm -f *.html
 
 clobber: clean
 	rm -f vms-empire vms-empire-*.tar*

README.md

@@ -0,0 +1,129 @@
+# VMS Empire
+
+VMS Empire is a classic turn-based strategy game played in a text terminal. Units, cities, land, and water are represented using letters and ASCII characters.
+
+This fork includes small compatibility fixes that allow the game to compile cleanly on modern Linux systems, including Raspberry Pi OS.
+
+## Changes in this fork
+
+* Added the GCC `-fcommon` compiler option to fix multiple-definition linker errors on modern GCC versions.
+* Corrected two map-array loops in `game.c`.
+* Changed:
+
+In line 126
+```c
+i <= MAP_SIZE
+```
+
+to:
+
+```c
+i < MAP_SIZE
+```
+
+This prevents the loops from accessing one element beyond the end of the arrays.
+
+## Requirements
+
+Install the compiler, development tools, Git, and ncurses library:
+
+```bash
+sudo apt update
+sudo apt install -y git build-essential libncurses-dev
+```
+
+## Download
+
+Clone this fork:
+
+```bash
+git clone https://github.com/dgdimick/empire.git
+cd empire
+```
+
+## Build
+
+Compile the game:
+
+```bash
+make
+```
+
+The executable will be created as:
+
+```text
+vms-empire
+```
+
+## Run
+
+Start the game with:
+
+```bash
+./vms-empire
+```
+
+## Clean and rebuild
+
+To remove compiled files and rebuild from scratch:
+
+```bash
+make clean
+make
+```
+
+## Repository remotes
+
+This fork is maintained at:
+
+```text
+https://github.com/dgdimick/empire
+```
+
+The original repository is:
+
+```text
+https://github.com/slacy/empire
+```
+
+## Platform tested
+
+The changes in this fork were tested on Raspberry Pi OS using a Raspberry Pi.
+
+## License
+
+This fork retains the original project’s licensing and copyright terms. See the repository files for the original license information.
+
+
+
+AI vs AI spectator mode
+-----------------------
+
+This fork adds an unattended spectator mode where the existing computer
+player controls both empires. Start it with:
+
+    ./vms-empire -a
+
+Use the existing -d option to set the delay in milliseconds between map
+updates. For example:
+
+    ./vms-empire -a -d 500
+
+The full battlefield is shown using the condensed map display. The USER-side AI
+is shown in blue and the COMP-side AI is shown in red on color terminals. Press Ctrl-C
+to stop an active game. At the end of a game, press any key to exit.
+
+
+AI spectator views
+------------------
+Start an AI-versus-AI match in one of four views:
+
+```bash
+  ./vms-empire -a -v blue
+  ./vms-empire -a -v red
+  ./vms-empire -a -v shared
+  ./vms-empire -a -v full
+
+If -v is omitted, shared fog-of-war is used. During a match, press B, R,
+S, or F to switch immediately between Blue, Red, Shared, and Full views.
+These display modes do not alter either AI's private fog-of-war map.

compmove.c

@@ -1061,7 +1061,8 @@ void check_endgame(void) {
 
   for (p = comp_obj[ARMY]; p != NULL; p = p->piece_link.next) ncomp_army++;
 
-  if (ncomp_city < nuser_city / 3 && ncomp_army < nuser_army / 3) {
+  if (!ai_vs_ai && ncomp_city < nuser_city / 3 &&
+      ncomp_army < nuser_army / 3) {
     clear_screen();
     prompt("The computer acknowledges defeat. Do");
     ksend("The computer acknowledges defeat.");

display.c

@@ -430,6 +430,9 @@ void print_zoom_cell(view_map_t *vmap, int row, int col, int row_inc,
                      int col_inc) {
   int r, c;
   char cell;
+#ifdef A_COLOR
+  chtype attr = COLOR_PAIR(COLOR_WHITE);
+#endif
 
   cell = ' ';
   for (r = row; r < row + row_inc; r++)
@@ -438,8 +441,28 @@ void print_zoom_cell(view_map_t *vmap, int row, int col, int row_inc,
           strchr(zoom_list, cell))
         cell = vmap[row_col_loc(r, c)].contents;
 
+#ifdef A_COLOR
+  if (ai_vs_ai) {
+    /* In spectator mode, USER is the Blue AI and COMP is the Red AI. */
+    if (cell == 'O' || strchr("TCBSDPFAZ", cell) != NULL)
+      attr = COLOR_PAIR(COLOR_BLUE) | A_BOLD;
+    else if (cell == 'X' || strchr("tcbsdpafz", cell) != NULL)
+      attr = COLOR_PAIR(COLOR_RED) | A_BOLD;
+    else if (cell == MAP_LAND || cell == '+')
+      attr = COLOR_PAIR(COLOR_GREEN);
+    else if (cell == MAP_SEA || cell == '.')
+      attr = COLOR_PAIR(COLOR_CYAN);
+  }
+  attron(attr);
+#endif
+
   (void)move(row / row_inc + NUMTOPS, col / col_inc);
   (void)addch((chtype)cell);
+
+#ifdef A_COLOR
+  attroff(attr);
+  attron(COLOR_PAIR(COLOR_WHITE));
+#endif
 }
 
 /*