Deflect Missiles rework

README.md

@@ -114,6 +114,7 @@ Pull requests for new content are welcome.
   - v1.9.1: Song of Slaying starts at +1.
   - v1.9.1: Force Lance is pure translocations, and removed from the Conjurer book.
   - v1.9.2: Spectral Weapon lasts longer at high spell power.
+  - v1.9.2: Deflect Missiles is never dispelled by attacks, but can drain mana when it deflects missiles. It drains less mana at higher power.
 
 #### Removed Spells
   - Summon Guardian Golem

crawl-ref/source/dat/descript/spells.txt

@@ -389,8 +389,13 @@ Deflect Missiles spell
 
 Protects the caster from all kinds of projectile attacks, making them
 significantly easier to dodge. It is highly effective against both
-single-target and penetrating attacks. Each time a missile is deflected the
-spell has a chance of expiring, with a lower chance of expiry at high power.
+single-target and penetrating attacks.
+
+The spell is linked to the caster's magical reserves, and may drain
+magic when a missile is deflected. The efficiency of the shield increases
+at higher spell power.
+
+To be cancelled, this spell must be carefully cast again in reverse.
 %%%%
 Dig spell
 

crawl-ref/source/player.cc

@@ -5788,7 +5788,8 @@ void player::shield_block_succeeded(actor *foe)
 
 int player::missile_deflection() const
 {
-    if (attribute[ATTR_DEFLECT_MISSILES])
+    if (attribute[ATTR_DEFLECT_MISSILES]
+            && (you.magic_points || you.species == SP_DJINNI))
         return 2;
 
     if (get_mutation_level(MUT_DISTORTION_FIELD) == 3
@@ -5807,11 +5808,7 @@ void player::ablate_deflection()
     if (attribute[ATTR_DEFLECT_MISSILES])
     {
         const int power = calc_spell_power(SPELL_DEFLECT_MISSILES, true);
-        if (one_chance_in(2 + power / 8))
-        {
-            attribute[ATTR_DEFLECT_MISSILES] = 0;
-            mprf(MSGCH_DURATION, "You feel less protected from missiles.");
-        }
+        dec_mp(div_rand_round(25, power));
     }
 }
 

crawl-ref/source/spl-selfench.cc

@@ -90,8 +90,17 @@ spret ice_armour(int pow, bool fail)
 spret deflection(int pow, bool fail)
 {
     fail_check();
-    you.attribute[ATTR_DEFLECT_MISSILES] = 1;
-    mpr("You feel very safe from missiles.");
+
+    if(!you.attribute[ATTR_DEFLECT_MISSILES])
+    {
+        you.attribute[ATTR_DEFLECT_MISSILES] = 1;
+        mpr("You feel very safe from missiles.");
+    }
+    else
+    {
+        you.attribute[ATTR_DEFLECT_MISSILES] = 0;
+        mpr("You carefully dispel your deflective shield.");
+    }
 
     return spret::success;
 }

crawl-ref/source/spl-util.cc

@@ -1146,11 +1146,6 @@ string spell_uselessness_reason(spell_type spell, bool temp, bool prevent,
             return "darkness is useless against divine light.";
         break;
 
-    case SPELL_DEFLECT_MISSILES:
-        if (temp && you.attribute[ATTR_DEFLECT_MISSILES])
-            return "you're already deflecting missiles.";
-        break;
-
     case SPELL_STATUE_FORM:
         if (SP_GARGOYLE == you.species)
             return "you're already a statue.";

crawl-ref/source/status.cc

@@ -1044,19 +1044,20 @@ static void _describe_terrain(status_info& inf)
 
 static void _describe_missiles(status_info& inf)
 {
-    const int level = you.missile_deflection();
-    if (!level)
-        return;
+    int level = you.missile_deflection();
+
+    if(you.attribute[ATTR_DEFLECT_MISSILES] && level == 0)
+        level = 2;
 
-    if (level > 1)
+    if (level == 2)
     {
-        bool perm = false;
-        inf.light_colour = perm ? WHITE : LIGHTMAGENTA;
+        bool enough_mana = you.magic_points || you.species == SP_DJINNI;
+        inf.light_colour = enough_mana ? LIGHTMAGENTA : DARKGREY;
         inf.light_text   = "DMsl";
         inf.short_text   = "deflect missiles";
         inf.long_text    = "You deflect missiles.";
     }
-    else
+    else if (level == 1)
     {
         bool perm = you.get_mutation_level(MUT_DISTORTION_FIELD) == 3
                     || you.wearing_ego(EQ_ALL_ARMOUR, SPARM_REPULSION)