Reform SH to be more transparent

Before: SH was a function of items and skills.  Blocking was a function
of SH, skills, and stats.

Now: SH is a function of items, skills, and stats.  Blocking is a
function of SH and SH alone.

Your ability to block attacks in given equipment should be more or less
the same, although there will be small differences.  Condensation Shield
was doubled (since nobody uses it), Divine Shield was made to not use
intelligence.

SH values have been rescaled to be on approximately the same scale as
AC and EV.  This meant increasing the max enchant of shields to +3.

4 files changed, 48 insertions, 42 deletions

diff --git a/crawl-ref/source/art-data.h b/crawl-ref/source/art-data.h
index 665c5149ab..e7fdec34a3 100644
--- a/crawl-ref/source/art-data.h
+++ b/crawl-ref/source/art-data.h
@@ -862,7 +862,7 @@
 /* 45: UNRAND_IGNORANCE */
 {
     "shield of Ignorance", "dull large shield", 
-    OBJ_ARMOUR, ARM_LARGE_SHIELD, +5, 0, BROWN, 0, 
+    OBJ_ARMOUR, ARM_LARGE_SHIELD, +8, 0, BROWN, 0, 
     UNRAND_FLAG_NONE, 
     {
         SPARM_NORMAL, 2, 2, 0, -6, 0, 
@@ -919,7 +919,7 @@
 /* 48: UNRAND_BULLSEYE */
 {
     "shield \"Bullseye\"", "round shield", 
-    OBJ_ARMOUR, ARM_SHIELD, +10, 0, RED, 0, 
+    OBJ_ARMOUR, ARM_SHIELD, +15, 0, RED, 0, 
     UNRAND_FLAG_NONE, 
     {
         SPARM_NORMAL, 0, -5, 0, 0, 0, 
@@ -1109,7 +1109,7 @@
 /* 58: UNRAND_RESISTANCE */
 {
     "shield of Resistance", "bronze shield", 
-    OBJ_ARMOUR, ARM_SHIELD, +3, 0, LIGHTRED, 0, 
+    OBJ_ARMOUR, ARM_SHIELD, +5, 0, LIGHTRED, 0, 
     UNRAND_FLAG_NONE, 
     {
         SPARM_NORMAL, 0, 0, 0, 0, 0, 
diff --git a/crawl-ref/source/art-data.txt b/crawl-ref/source/art-data.txt
index 25d5956f0f..95b381db10 100644
--- a/crawl-ref/source/art-data.txt
+++ b/crawl-ref/source/art-data.txt
@@ -708,7 +708,7 @@ DESC_END: Presumably this relic led to the invention of the famous spell, or may
 NAME:    shield of Ignorance
 APPEAR:  dull large shield
 OBJ:     OBJ_ARMOUR/ARM_LARGE_SHIELD
-PLUS:    +5
+PLUS:    +8
 COLOUR:  BROWN
 TILE:    urand_ignorance
 TILE_EQ: shield_of_ignorance
@@ -747,7 +747,7 @@ DESC_END: It allows its wearer to excel in the arts of thievery.
 NAME:    shield "Bullseye"
 APPEAR:  round shield
 OBJ:     OBJ_ARMOUR/ARM_SHIELD
-PLUS:    +10
+PLUS:    +15
 COLOUR:  RED
 TILE:    urand_bullseye
 TILE_EQ: bullseye
@@ -866,7 +866,7 @@ DAM:     3
 NAME:    shield of Resistance
 APPEAR:  bronze shield
 OBJ:     OBJ_ARMOUR/ARM_SHIELD
-PLUS:    +3
+PLUS:    +5
 COLOUR:  LIGHTRED
 TILE:    urand_resistance
 TILE_EQ: shield_of_resistance
diff --git a/crawl-ref/source/itemprop.cc b/crawl-ref/source/itemprop.cc
index 96a3f4d3ed..755078c862 100644
--- a/crawl-ref/source/itemprop.cc
+++ b/crawl-ref/source/itemprop.cc
@@ -142,11 +142,11 @@ static armour_def Armour_prop[NUM_ARMOURS] =
         true,  EQ_BOOTS,       SIZE_MEDIUM, SIZE_LARGE },
 
     // Note: shields use ac-value as sh-value, EV pen is used for heavy_shield.
-    { ARM_BUCKLER,              "buckler",                3,  0,   90,
+    { ARM_BUCKLER,              "buckler",                5,  0,   90,
         true,  EQ_SHIELD,      SIZE_LITTLE, SIZE_MEDIUM },
-    { ARM_SHIELD,               "shield",                 5, -1,  150,
+    { ARM_SHIELD,               "shield",                 8, -1,  150,
         false, EQ_SHIELD,      SIZE_SMALL,  SIZE_BIG    },
-    { ARM_LARGE_SHIELD,         "large shield",           7, -2,  230,
+    { ARM_LARGE_SHIELD,         "large shield",          13, -2,  230,
         false, EQ_SHIELD,      SIZE_MEDIUM, SIZE_GIANT  },
 };
 
@@ -1017,6 +1017,11 @@ int armour_max_enchant( const item_def &item )
         max_plus = MAX_ARM_ENCHANT;
     }
 
+    if (eq_slot == EQ_SHIELD)
+    {
+        max_plus = 3;
+    }
+
     return (max_plus);
 }
 
diff --git a/crawl-ref/source/player.cc b/crawl-ref/source/player.cc
index fe7b7bca31..4340a1c6ab 100644
--- a/crawl-ref/source/player.cc
+++ b/crawl-ref/source/player.cc
@@ -2301,37 +2301,59 @@ int player_mag_abil(bool is_weighted)
 
 int player_shield_class(void)   //jmf: changes for new spell
 {
-    int base_shield = 0;
+    int shield = 0;
+    int stat = 0;
+
+    if (you.incapacitated())
+        return (0);
 
     if (player_wearing_slot(EQ_SHIELD))
     {
         const item_def& item = you.inv[you.equip[EQ_SHIELD]];
-        base_shield = property(item, PARM_AC);
+        int base_shield = property(item, PARM_AC);
 
-        int racial_bonus = _player_armour_racial_bonus(item) * 2 / 3;
+        int racial_bonus = _player_armour_racial_bonus(item);
 
         // bonus applied only to base, see above for effect:
-        base_shield *= (20 + you.skills[SK_SHIELDS] + racial_bonus);
-        base_shield /= 20;
+        shield += base_shield * 100;
+        shield += base_shield * 5 * you.skills[SK_SHIELDS];
+        shield += base_shield * racial_bonus * 10 / 3;
 
-        base_shield += item.plus;
+        shield += item.plus * 100;
+
+        if (item.sub_type == ARM_BUCKLER)
+            stat = you.dex * 38;
+        else if (item.sub_type == ARM_LARGE_SHIELD)
+            stat = you.dex * 12 + you.strength * 26;
+        else
+            stat = you.dex * 19 + you.strength * 19;
     }
     else
     {
         if (you.duration[DUR_MAGIC_SHIELD])
-            base_shield = 2 + you.skills[SK_EVOCATIONS] / 6;
+        {
+            stat   =  600 + you.skills[SK_EVOCATIONS] * 50;
+            shield += 300 + you.skills[SK_EVOCATIONS] * 25;
+        }
 
         if (!you.duration[DUR_FIRE_SHIELD]
             && you.duration[DUR_CONDENSATION_SHIELD])
         {
-            base_shield += 2 + (you.skills[SK_ICE_MAGIC] / 6);  // max 6
+            shield += 300 + (you.skills[SK_ICE_MAGIC] * 25);
+            stat    = std::max(stat, you.intel * 38);
         }
     }
 
     if (you.duration[DUR_DIVINE_SHIELD])
-        base_shield += you.attribute[ATTR_DIVINE_SHIELD];
+    {
+        shield += you.attribute[ATTR_DIVINE_SHIELD] * 150;
+        stat = std::max(stat, int(you.attribute[ATTR_DIVINE_SHIELD] * 300));
+    }
+
+    if (shield + stat > 0)
+        shield += skill_bump(SK_SHIELDS) * 38;
 
-    return (base_shield);
+    return (shield + stat + 50) / 100;
 }
 
 int player_sust_abil(bool calc_unid)
@@ -6097,31 +6119,10 @@ int player::shield_block_penalty() const
 int player::shield_bonus() const
 {
     const int shield_class = player_shield_class();
-    if (!shield_class)
+    if (shield_class <= 0)
         return (-100);
 
-    // Note that 0 is not quite no-blocking.
-    if (incapacitated())
-        return (0);
-
-    int stat = 0;
-    if (const item_def *sh = const_cast<player*>(this)->shield())
-    {
-        stat =
-            sh->sub_type == ARM_BUCKLER?      dex :
-            sh->sub_type == ARM_LARGE_SHIELD? (3 * strength + dex) / 4:
-            (dex + strength) / 2;
-    }
-    else
-    {
-        // Magical and divine shields are governed by the mind.
-        stat = intel / 2;
-    }
-
-    return (random2(shield_class)
-            + (random2(stat) / 4)
-            + (random2(skill_bump(SK_SHIELDS)) / 4)
-            - 1);
+    return random2avg(shield_class * 2, 2) / 3 - 1;
 }
 
 int player::shield_bypass_ability(int tohit) const