make display effect code reusable and move it to display.c

include/extern.h

@@ -360,6 +360,7 @@ E void FDECL(newsym, (int, int));
 E void FDECL(newsym_force, (int, int));
 E void FDECL(shieldeff, (XCHAR_P, XCHAR_P));
 E void FDECL(tmp_at, (int, int));
+E void FDECL(flash_glyph_at, (int, int, int));
 E void FDECL(swallowed, (int));
 E void FDECL(under_ground, (int));
 E void FDECL(under_water, (int));

src/display.c

@@ -1067,6 +1067,28 @@ int x, y;
     } /* end case */
 }
 
+/*
+ * flash_glyph_at(x, y, glyph)
+ *
+ * Briefly flash between the passed glyph and the glyph that's
+ * meant to be at the location.
+ */
+void
+flash_glyph_at(x, y, tg)
+int x, y, tg;
+{
+     int i, glyph[2];
+
+     glyph[0] = tg;
+     glyph[1] = glyph_at(x, y);
+     for (i = 0; i < 15; i++) {
+         show_glyph(x, y, glyph[i % 2]);
+         flush_screen(1);
+         delay_output();
+     }
+     newsym(x, y);
+}
+
 /*
  * swallowed()
  *

src/read.c

@@ -2579,21 +2579,13 @@ struct _create_particular_data *d;
         if (d->sleeping)
             mtmp->msleeping = 1;
         if (d->hidden && is_hider(mtmp->data)) {
-            if (wizard && cansee(mtmp->mx, mtmp->my)) {
+            int saveglyph = glyph_at(mtmp->mx, mtmp->my);
-                int i, glyph[2];
 
-                glyph[0] = glyph_at(mtmp->mx, mtmp->my);
+            mtmp->mundetected = 1;
-                mtmp->mundetected = 1;
-                newsym(mtmp->mx, mtmp->my);
-                glyph[1] = glyph_at(mtmp->mx, mtmp->my);
-                if (!canseemon(mtmp) && !sensemon(mtmp))
-                    for (i = 0; i < 15; i++) {
-                        show_glyph(mtmp->mx, mtmp->my, glyph[i % 2]);
-                        flush_screen(1);
-                        delay_output();
-                    }
-            }
             newsym(mtmp->mx, mtmp->my);
+            if (wizard && cansee(mtmp->mx, mtmp->my))
+                if (!canseemon(mtmp) && !sensemon(mtmp))
+                    flash_glyph_at(mtmp->mx, mtmp->my, saveglyph);
         }
         madeany = TRUE;
         /* in case we got a doppelganger instead of what was asked