Use dice rolls instead of chance for spell magnitude (bug #4945)

CHANGELOG.md

@@ -53,6 +53,7 @@
     Bug #4927: Spell effect having both a skill and an attribute assigned is a fatal error
     Bug #4938: Strings from subrecords with actually empty headers can't be empty
     Bug #4942: Hand-to-Hand attack type is chosen randomly when "always use best attack" is turned off
+    Bug #4945: Poor random magic magnitude distribution
     Bug #4947: Player character doesn't use lip animation
     Bug #4948: Footstep sounds while levitating on ground level
     Bug #4963: Enchant skill progress is incorrect

apps/openmw/mwmechanics/spellcasting.cpp

@@ -534,8 +534,7 @@ namespace MWMechanics
 
             if (magnitudeMult > 0 && !absorbed)
             {
-                float random = Misc::Rng::rollClosedProbability();
-                float magnitude = effectIt->mMagnMin + (effectIt->mMagnMax - effectIt->mMagnMin) * random;
+                float magnitude = effectIt->mMagnMin + Misc::Rng::rollDice(effectIt->mMagnMax - effectIt->mMagnMin + 1);
                 magnitude *= magnitudeMult;
 
                 if (!target.getClass().isActor())

apps/openmw/mwmechanics/spells.cpp

@@ -94,7 +94,10 @@ namespace MWMechanics
                 for (unsigned int i=0; i<spell->mEffects.mList.size();++i)
                 {
                     if (spell->mEffects.mList[i].mMagnMin != spell->mEffects.mList[i].mMagnMax)
-                        random[i] = Misc::Rng::rollClosedProbability();
+                    {
+                        int delta = spell->mEffects.mList[i].mMagnMax - spell->mEffects.mList[i].mMagnMin;
+                        random[i] = Misc::Rng::rollDice(delta + 1) / static_cast<float>(delta);
+                    }
                 }
             }
 

apps/openmw/mwworld/inventorystore.cpp

@@ -637,15 +637,15 @@ void MWWorld::InventoryStore::updateMagicEffects(const Ptr& actor)
             bool existed = (mPermanentMagicEffectMagnitudes.find((**iter).getCellRef().getRefId()) != mPermanentMagicEffectMagnitudes.end());
             if (!existed)
             {
-                // Roll some dice, one for each effect
                 params.resize(enchantment.mEffects.mList.size());
-                for (unsigned int i=0; i<params.size();++i)
-                    params[i].mRandom = Misc::Rng::rollClosedProbability();
 
-                // Try resisting each effect
                 int i=0;
                 for (const ESM::ENAMstruct& effect : enchantment.mEffects.mList)
                 {
+                    int delta = effect.mMagnMax - effect.mMagnMin;
+                    // Roll some dice, one for each effect
+                    params[i].mRandom = Misc::Rng::rollDice(delta + 1) / static_cast<float>(delta);
+                    // Try resisting each effect
                     params[i].mMultiplier = MWMechanics::getEffectMultiplier(effect.mEffectID, actor, actor);
                     ++i;
                 }