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EFF file format

Applies to:
BG1: TotS, BG2, BG2: ToB, IWD, IWD:HoW, IWD:TotL, BGEE

General Description
This file format describes an effect (opcode) and its parameters. The format is an extended version of that found embedded in creatures, items and spells, and is a replacement for the version 1 embedded effects used in BG1. The engine appears to roll a probability for each valid target type, rather than one probability per attack.

EFF V2.0
Overall structure:
  • Header
  • Body

    • EFF V2.0 Header

    Offset Size (datatype) Description
    0x0000 4 (char array)

    Signature (‘EFF ‘)
    0x0004 4 (char array)

    Version (‘V2.0’)

    EFF V2.0 Body

    When an effect is called via an eff, several of the fields (including duration and timing mode) are overriden by the calling SPL/ITM. Other fields are copied directly from the calling SPL/ITEM and overwrite the values defined in the EFF.

    Offset Size (datatype) Description
    0x0008 4 (char array)

    External EFFs - the field is the same as the signature field from the header
    Embedded EFFs - this field is zeroed out
    0x000c 4 (char array)

    External EFFs - the field is the same as the version field from the header
    Embedded EFFs - this field is zeroed out
    0x0010 4 (dword)

    Opcode number
    0x0014 4 (dword)

    Target type

    • 0=None
    • 1=Self (pre-projectile)
    • 2=Pre-target
    • 3=Party
    • 4=Everyone (inc. party)
    • 5=Everyone (excl. party)
    • 6=Everyone matching specific value of caster (or Party if cast by party member)
    • 7=Everyone matching specific value of target
    • 8=Everyone (excl. caster)
    • 9=Self (post-projectile)
    0x0018 4 (dword)

    Power
    0x001c 4 (dword)

    Parameter 1
    0x0020 4 (dword)

    Parameter 2
    0x0024 2 (word)

    Timing mode

    • 0=Duration
    • 1=Permanent
    • 2=While equipped
    • 3=Delayed Duration
    • 4=Delayed
    • 5=Delayed (transforms to 8)
    • 6=Duration?
    • 7=Permanent?
    • 8=Permanent (unsaved)
    • 9=Permanent (after Death)
    • 10=Trigger
    • 4096=Absolute duration

    NB. all effects except those with Timing mode ‘9’ are removed by death.
    0x0026 2 (word)

    Timing ?
    0x0028 4 (dword)

    Duration
    0x002c 2 (word)

    Probability 1
    0x002e 2 (word)

    Probability 2

    Note: The BG1 engine treats probability as a single word, effects are applied in the range 0-probability.
    Note: Other engines treat probability as two values, effects are applied in the range probability <= x <= probability.
    Probability range is 0-99
    0x0030 8 (resref)

    Resource
    0x0038 4 (dword)

    Dice Thrown
    0x003c 4 (dword)

    Dice Sides
    0x0040 4 (dword)

    Saving throw type

    • bit 0: Spells
    • bit 1: Breath
    • bit 2: Death
    • bit 3: Wands
    • bit 4: Polymorph
    • bit 10: Ignore primary target – Line AoE projectile doesn’t affect end target (EE only)
    • bit 11: Ignore secondary target – Line AoE projectile doesn’t affect bystanders (EE only)
    • bit 24: Bypass mirror image (EE/ToBEx only)
    • bit 25: EE - ignore difficulty; TobEx - limit effect stacking
    • bit 26: TobEx internal (don’t use) - suspend effect application

    NB. If more than 1 saving throw type is specified, the target rolls against their best save
    0x0044 4 (dword)

    Save bonus
    0x0048 4 (dword)

    TobEx: Stacking ID. Checked when bit 25 of the Saving Throw Type is set.

    If two effects of the same opcode are applied, both have Limit Effect Stacking bit set, and both have the same stacking ID, then the latter applied effect is suspended in application until the former effect expires. Regardless of whether it is applied, the latter effect will expire at the same time that it would expire if it was applied. In other words, the total duration of some non-stacking effect opcode is not extended because more than one copy of the effect was applied.

    Stacking IDs are unique to the opcode being applied. To maintain uniqueness of stacking IDs between different mods, one recommendation is to use the higher word of Special as the modder’s Infinity Engine Community Prefix, then use the lower word as an identifying ID. For example, 0x41360001 (‘A6’ 0x0001).
    0x004c 4 (dword)

    Primary type (school)
    0x0050 4 (dword)

    Unknown
    0x0054 4 (dword)

    Parent resource lowest affected level
    0x0058 4 (dword)

    Parent resource highest affected level
    0x005c 4 (dword)

    Resistance

    The default behaviour is that effects cannot be dispelled and ignore resistance.

    • bit 0: Can be dispelled, affected by resistance
    • bit 1: Ignores resistance (when used in combination with bit 0)

    This can also be presented in the more traditional way:

    • 0=Nonmagical
    • 1=Can be dispelled/Affected by resistance
    • 2=Cannot be dispelled/Ignores resistance
    • 3=Can be dispelled/Ignores resistance
    0x0060 4 (dword)

    Parameter 3
    0x0064 4 (dword)

    Parameter 4
    0x0068 4 (dword)

    Parameter 5
    0x006c 4 (dword)

    Parameter 6
    0x0070 8 (resref)

    Resource 2 (VVC in many effects)
    0x0078 8 (resref)

    Resource 3
    0x0080 4 (dword)

    Caster X coordinate
    0x0084 4 (dword)

    Caster Y coordinate
    0x0088 4 (dword)

    Target X coordinate
    0x008c 4 (dword)

    Target Y coordinate
    0x0090 4 (dword)

    Parent resource type (0=None, 1=Spell, 2=Item)
    0x0094 8 (resref)

    Parent resource
    0x009c 4 (dword)

    Parent resource flags (from SPL 0x18 or ITM ext header 0x26)
    0x00a0 4 (dword)

    Projectile
    0x00a4 4 (dword)

    Parent resource slot
    0x00a8 32 (bytes)

    Variable
    0x00c8 4 (dword)

    Caster level
    0x00cc 4 (dword)

    FirstApply (internal flag)
    0x00d0 4 (dword)

    Secondary Type
    0x00d4 4*15 (dword)

    Unknown