save button states in savegames (#2165)

* save button states in savegames

Mostly taken from Doom Retro.

* simplify loop

* simplify restoring button state

src/p_saveg.c

@@ -2005,6 +2005,41 @@ static void saveg_write_rng_t(rng_t *str)
     saveg_write32(str->prndindex);
 }
 
+//
+// button_t
+//
+
+static void saveg_read_button_t(button_t *str)
+{
+    // line_t *line
+    int line = saveg_read32();
+    str->line = &lines[line];
+
+    // bwhere_e where
+    str->where = (bwhere_e)saveg_read32();
+
+    // int btexture
+    str->btexture = saveg_read32();
+
+    // int btimer
+    str->btimer = saveg_read32();
+}
+
+static void saveg_write_button_t(button_t *str)
+{
+    // line_t *line
+    saveg_write32(str->line - lines);
+
+    // bwhere_e where
+    saveg_write32((int)str->where);
+
+    // int btexture
+    saveg_write32(str->btexture);
+
+    // int btimer
+    saveg_write32(str->btimer);
+}
+
 //
 // P_ArchivePlayers
 //
@@ -2463,7 +2498,8 @@ enum {
   tc_pusher,      // phares 3/22/98:  new push/pull effect thinker
   tc_flicker,     // killough 10/4/98
   tc_endspecials,
-  tc_friction     // store friction for complevel Boom
+  tc_friction,    // store friction for complevel Boom
+  tc_button,
 } specials_e;
 
 //
@@ -2653,6 +2689,18 @@ void P_ArchiveSpecials (void)
         }
     }
 
+  CheckSaveGame(MAXBUTTONS * sizeof(button_t));
+
+  for (int i = 0; i < MAXBUTTONS; i++)
+  {
+    if (buttonlist[i].btimer != 0)
+    {
+      saveg_write8(tc_button);
+      saveg_write_pad();
+      saveg_write_button_t(&buttonlist[i]);
+    }
+  }
+
   // add a terminating marker
   saveg_write8(tc_endspecials);
 }
@@ -2811,6 +2859,13 @@ void P_UnArchiveSpecials (void)
           break;
         }
 
+      case tc_button:
+        saveg_read_pad();
+        button_t button;
+        saveg_read_button_t(&button);
+        P_StartButton(button.line, button.where, button.btexture, button.btimer);
+        break;
+
       default:
         I_Error ("P_UnarchiveSpecials:Unknown tclass %i "
                  "in savegame",tclass);

src/p_spec.h

@@ -536,6 +536,8 @@ typedef struct
   struct mobj_s *soundorg;
 } button_t;
 
+void P_StartButton(struct line_s *line, bwhere_e w, int texture, int time);
+
 // p_lights
 
 typedef struct