Spell success, Str/Int, and Armour skill

[ThreeInvisibleDucks]

I originally posted this to a CIP thread, but it was suggested to me that not everybody browses that forum and the results might be of some interest.

Copy-pasta follows:

I took a look at the source code re: spellcasting fail rate. According to the function int raw_spell_fail(spell_type spell) in spl-cast.cc the breakpoint is when one raises Str and the value returned by function player_armour_shield_spell_penalty() doesn't decrease by more than two points, because raising Int always decreases fail chance by 2 points.

Assuming this is correct, I wrote a little script to calculate the breakpoints where raising Int becomes better than Str in armour. There may be some rounding issues. Also this assumes that the player is not wearing a shield.

  Code:

# Calculate player adjusted body armour penalty
def player_abap(er, armr, st_str):
    return 2.0 * er * er * (45 - armr) / (5 * (st_str + 3)) / 45

def player_armour_shield_spell_penalty(er, armr, st_str):
    abap = player_abap(er, armr, st_str)
    bap = max(19 * abap, 0)
    bsp = 0 # XXX ignore shield penalty for now
    return max(bap + bsp, 0)

def print_str_armr_breakpoints(er):
    print("Minimum Str in ER %d armour when raising Int decreases spell fail%% more" % er)
    print("Armr\tStr")
    for armr in range(0, 28):
        print("%d" % armr, end="\t")
        assp0 = player_armour_shield_spell_penalty(er, armr, 1)
        for str1 in range(2, 51):
            assp = player_armour_shield_spell_penalty(er, armr, str1)
            diff = assp0 - assp
            if diff <= 2:
                # print("Armr %d: Str %d, assp %d, assp0 %d, diff %d" % (armr, str1, assp, assp0, diff))
                print("%d" % str1)
                break
            assp0 = assp
    print()

if __name__ == '__main__':
    for er in (4, 5, 7, 10, 11, 15, 18, 23):
        print_str_armr_breakpoints(er)


Output:

  Code:

Minimum Str in ER 4 armour when raising Int decreases spell fail% more
Armr   Str
0   6
1   6
2   6
3   6
4   5
5   5
6   5
7   5
8   5
9   5
10   5
11   5
12   5
13   5
14   4
15   4
16   4
17   4
18   4
19   4
20   4
21   4
22   4
23   3
24   3
25   3
26   3
27   3

Minimum Str in ER 5 armour when raising Int decreases spell fail% more
Armr   Str
0   8
1   8
2   8
3   7
4   7
5   7
6   7
7   7
8   7
9   7
10   7
11   6
12   6
13   6
14   6
15   6
16   6
17   6
18   6
19   5
20   5
21   5
22   5
23   5
24   5
25   5
26   4
27   4

Minimum Str in ER 7 armour when raising Int decreases spell fail% more
Armr   Str
0   12
1   12
2   11
3   11
4   11
5   11
6   11
7   11
8   10
9   10
10   10
11   10
12   10
13   10
14   9
15   9
16   9
17   9
18   9
19   8
20   8
21   8
22   8
23   8
24   7
25   7
26   7
27   7

Minimum Str in ER 10 armour when raising Int decreases spell fail% more
Armr   Str
0   18
1   17
2   17
3   17
4   17
5   16
6   16
7   16
8   16
9   15
10   15
11   15
12   15
13   14
14   14
15   14
16   14
17   13
18   13
19   13
20   13
21   12
22   12
23   12
24   11
25   11
26   11
27   10

Minimum Str in ER 11 armour when raising Int decreases spell fail% more
Armr   Str
0   19
1   19
2   19
3   19
4   18
5   18
6   18
7   18
8   17
9   17
10   17
11   17
12   16
13   16
14   16
15   16
16   15
17   15
18   15
19   14
20   14
21   14
22   13
23   13
24   13
25   12
26   12
27   12

Minimum Str in ER 15 armour when raising Int decreases spell fail% more
Armr   Str
0   27
1   27
2   27
3   26
4   26
5   26
6   25
7   25
8   25
9   24
10   24
11   23
12   23
13   23
14   22
15   22
16   21
17   21
18   21
19   20
20   20
21   19
22   19
23   18
24   18
25   18
26   17
27   16

Minimum Str in ER 18 armour when raising Int decreases spell fail% more
Armr   Str
0   33
1   33
2   32
3   32
4   31
5   31
6   31
7   30
8   30
9   29
10   29
11   29
12   28
13   28
14   27
15   27
16   26
17   26
18   25
19   25
20   24
21   24
22   23
23   23
24   22
25   21
26   21
27   20

Minimum Str in ER 23 armour when raising Int decreases spell fail% more
Armr   Str
0   43
1   42
2   42
3   41
4   41
5   40
6   40
7   39
8   39
9   38
10   38
11   37
12   36
13   36
14   35
15   35
16   34
17   33
18   33
19   32
20   31
21   31
22   30
23   29
24   29
25   28
26   27
27   26


[Berder]

edit: nevermind.

[savageorange]

Note that this is python3, not python2. That's good, but you do need to be aware of it when running the code.

(That is one reason that including a shbang line, like '#!/usr/bin/env python3', at the start of your code, is helpful even if you are running Windows: it signposts which version your code is written for.)

A few suggestions:

* This message, "Minimum Str in ER 4 armour when raising Int decreases spell fail% more", perhaps needs a comma or rephrasing.
Consider 'In ER 4 armour, raising Int decreases spell fail more when Str >= '.

* You can improve the formatting using field width codes:

  Code:

print("%-6s %-6s" % ('Armor', 'Str'))
    for armr in range(0, 28):
        print("%-6d" % armr, end="")
        assp0 = player_armour_shield_spell_penalty(er, armr, 1)
        for str1 in range(2, 51):
            assp = player_armour_shield_spell_penalty(er, armr, str1)
            diff = assp0 - assp
            if diff <= 2:
                # print("Armr %d: Str %d, assp %d, assp0 %d, diff %d" % (armr, str1, assp, assp0, diff))
                print(" %-6d" % str1)
                break
            assp0 = assp


[dowan]

Wow, I thought those str numbers would be lower, str is even more useful than I realized for lowering fail%. That's a very interesting chart.