Casting in Heavy Armor

[MainiacJoe]

My recent HEFE, and to a lesser extent my previous DDNe, were casting at <5% in much heavier armors than I had ever thought possible before. So now my eyes are opened to much greater possibilities for hybrid builds than I'd considered before.

The two sorts of questions that this introduces me to are, "I found this great spell I want to cast, what the heaviest armor I can expect to cast it in?" and, "I found this great armour, what the highest level spell I can expect to cast in it?"

As I understand it, STR and wizardry are going to be the most important factors in determining the XP cost of getting a spell to low failure rates in armor. Are there rules of thumb that you use to answer these questions, or is the situation too complex to distill into bullet points?

[Eyesburn]

As I understand it, STR and wizardry are going to be the most important factors

I think you should include INT, armour skill, spellcasting and spell school too

[duvessa]

You can cast anything in anything these days with enough str. In practice, if you want better spell success in armour you're going to be pursuing str and spell skills and not much else - armour skill does reduce the penalty by 1/45th per level but since you're wearing heavy armour you've already trained a bunch of armour skill for AC before you started trying to get spells, and so you'll improve your success rates more by investing XP in spell schools instead of armour. It's true that once you pass a certain str value, int will increase your success rates by more than additional str will (since the effect of str falls off and the effect of int is linear), but in plate+ that certain str value is higher than you are likely to reach unless you're a troll or something.
Obviously int is important if you want spell power but in heavy armour you probably aren't interested in conjurations or whatever so you probably don't need a lot of spell power.
If you're really curious, look at the aevp formula ([(2/5) * er^2 / (str+3)] * [45 - armour_skill]/45), and then look at raw_spell_fail() in spl-cast.cc, and then cuss the devs out for keeping that ridiculously terrible spell success formula around for 20 versions and counting.

[MainiacJoe]

You can cast anything in anything these days with enough str. In practice, if you want better spell success in armour you're going to be pursuing str and spell skills and not much else - armour skill does reduce the penalty by 1/45th per level but since you're wearing heavy armour you've already trained a bunch of armour skill for AC before you started trying to get spells, and so you'll improve your success rates more by investing XP in spell schools instead of armour.

This confirms what I was thinking as far as how to transition from melee only to adding support spells, except it looks like I'm still underestimating how heavy one can go. I think one error I made with my recent HEFE, which was gradually increasing armor weight while keeping the spell failure low, was neglecting the Armour skill for the AC. Without the latter, I'm not really gaining enough to make the skill investment to cast in armor worthwhile.

If you're really curious, look at the aevp formula ([(2/5) * er^2 / (str+3)] * [45 - armour_skill]/45), and then look at raw_spell_fail() in spl-cast.cc, and then cuss the devs out for keeping that ridiculously terrible spell success formula around for 20 versions and counting.

I can make sense of the AEVP formula, and that's why I knew STR was more important than Armour skill, but the spell failure stuff has always made my head hurt whenever I've looked into it.

[tasonir]

I think I got about as far into that formula as seeing it used pyramidal numbers or some other concept which I had never heard of and I never tried to figure it out again. And I was someone who actually took the time to fully understand the old ranged combat formula, which was pretty terrible, although not as bad as spell success.

Since str and int are both very helpful, chei becomes great for heavy armor casters, although then you have to deal with the slowness. If you aren't using transmutations (because then you probably don't wear armor most of the time) there aren't too many high level spells you want, so usually being able to cast level 3-5 spells is enough, which can be done without chei.

And then there's those rediculous games where you cast singularity in fire dragon armor at 2% failure rate because you found two randart rings which both had wizardry, and wear the hat of pondering for +5int: http://dobrazupa.org/morgue/tasonir/mor ... 072752.txt. I miss singularity.

[ThreeInvisibleDucks]

Once I made a script to calculate body armour penalty in additional required spell skill levels: viewtopic.php?f=5&t=17049

It doesn't account for stepdowns after Spellcasting/spell school 20/20 or so, but at least it gives some idea how strength, Armour skill, and ER affect spellcasting.

[syringe]

You can cast anything in anything these days with enough str.

What happened? Is str any more accessible now than it used to be?

[duvessa]

You can cast anything in anything these days with enough str.

What happened? Is str any more accessible now than it used to be?

In older versions, strength did nothing to armour penalties after reaching 3*EVP (the highest EVP was 9 on GDA). As a result, your capacity to make a character specifically to cast highlevel spells in CPA/GDA was limited. It was possible to cast level 9 spells in GDA with good success rates without Vehumet but it required stats that only ziggurat characters were reaching.


In even older versions (pre-0.6), the effect of strength on armour spell penalties was very different:

  Code:

        int ev_penalty = abs(property( you.inv[you.equip[EQ_BODY_ARMOUR]],
                                       PARM_EVASION ));

        // The minus 15 is to make the -1 light armours not so bad
        armour += (20 * ev_penalty) - 15;

        //jmf: armour skill now reduces failure due to armour
        //bwr: this was far too good, an armour skill of 5 was
        //     completely negating plate mail.  Plate mail should
        //     hardly be completely negated, it should still be
        //     an important consideration for even high level characters.
        //     Truth is, even a much worse penalty than the above can
        //     easily be overcome by gaining spell skills... and a lot
        //     faster than any reasonable rate of bonus here.
        int lim_str = (you.strength > 30) ? 30 :
                      (you.strength < 10) ? 10 : you.strength;

        armour -= ((you.skills[SK_ARMOUR] * lim_str) / 15);

But you aren't interested in that, right?

[papilio]

Here is an easy guide.

Make your STR up to at least ER+3. That's the rule of thumb.

[duvessa]

that's a rule of thumb, yes

specifically it's a bad and wrong rule of thumb that nobody should use because it's bad

doesn't stop people from spreading it apparently

[Eyesburn]

My recent HEFE, and to a lesser extent my previous DDNe, were casting at <5% in much heavier armors than I had ever thought possible before. So now my eyes are opened to much greater possibilities for hybrid builds than I'd considered before.

The two sorts of questions that this introduces me to are, "I found this great spell I want to cast, what the heaviest armor I can expect to cast it in?" and, "I found this great armour, what the highest level spell I can expect to cast in it?"

As I understand it, STR and wizardry are going to be the most important factors in determining the XP cost of getting a spell to low failure rates in armor. Are there rules of thumb that you use to answer these questions, or is the situation too complex to distill into bullet points?

probably the best way to get answers to these questions is to use wizard mode and simulate character in heavy armour with spells you would like to cast

[MainiacJoe]

Here is an easy guide.

Make your STR up to at least ER+3. That's the rule of thumb.

0.4 * ER^2 / (Str + 3) * [minor armour skill adjustment] -----> 0.4 * ER^2 / (ER + 6)

leather = 0.64
ring = 1.51
scale = 2.50
fda = 2.85
chain = 4.29
plate = 5.40
gda = 7.30

STR 26 is simply not sufficient to cast in gda. Here are 0.4 * ER^2 for these armors:

leather = 6.4
ring = 19.6
scale = 40
fda = 48.4
chain = 90
plate = 129.6
gda = 211.6

Clearly, the proper rule of thumb for the amount of STR you need for chain and heavier is, "As much as practical". So my OP was largely wishful thinking.