Author: HobbitDur

Battle model animations hold one pose per battle tick, at 15 poses per second. A mod that wants smoother models either inserts interpolated frames in the animation data or uses the engine’s own half-step player (Battle Model Animation Timing). This page covers the first approach: what the engine allows, which animations do not fit, and how to cut the ones that do not.

  1. Converting by inserting frames
  2. The two limits
    1. 255 frames — the storage limit
    2. 128 frames — the Slow limit
  3. Splitting an animation that does not fit
    1. Rewriting the sequences
    2. Why A0 cannot be chained
  4. Which monsters do not fit
  5. Function and data addresses

Converting by inserting frames

Inserting factor - 1 interpolated poses between each pair of frames turns a 15 fps animation into a 30 fps one (factor = 2) or a 60 fps one (factor = 4). The frame count of the result depends on whether the animation loops:

Animation Frame count after conversion
played once (n - 1) * factor + 1
looping n * factor (the wrap from the last frame back to the first one is interpolated too)

Whether an animation loops is not stored in the animation data: it depends on how the animation sequences play it — see Animation Sequences for the op codes and FF8GameData/dat/animloopdetector.py in FF8UltimateEditor for the detection.

The two limits

255 frames — the storage limit

An animation stores its frame count on one byte, and BattleAnimCmd.current_frame / total_frames are bytes as well, so no animation can be longer than 255 frames.

128 frames — the Slow limit

When an animation starts while the entity is slowed, pre_Battle_ReadAnimation sets total_frames = 2 * nbFrames - 1 in an 8 bit register:

0x509482  shl cl, 1     ; cl is a byte
0x509484  dec cl
0x509486  mov [eax+7], cl

Over 128 frames that count wraps: a 137 frame animation gets 2*137-1 = 273 & 0xFF = 17 and stops after 17 calls instead of 273. So an animation Slow can reach must stay ≤ 128 frames.

Slow (and Haste) are only applied while currentAnimSeqId == basedAnimSeq (Battle_QueueAnimation), and the A3 op code marks the running sequence as the base one. Only the animations played by a base sequence — the idle stance in practice — are concerned. A loop inside an attack sequence is never slowed and uses the full 255.

This is why the limit is per animation:

Animation Limit
played by a base sequence (A3) 128 frames
every other one 255 frames

Splitting an animation that does not fit

An animation that goes over its limit once converted is cut into parts played one after the other. Interpolate first, cut after: the animation is converted whole, then the resulting frame stream is cut in contiguous slices of at most the limit. The parts are then slices of the very stream an unsplit conversion would produce — no frame is repeated at the cut, no interpolated frame is missing, and the parts chained play exactly the unsplit animation. Elvoret’s animation 27 at 30 fps: 140 frames → 279 converted → 140 + 139, and 140 + 139 = 279.

(Cutting the 15 fps frames before interpolating would instead force each part to end on the frame the next one starts with — one repeated frame per cut, and one tick too many.)

The chaining is seamless because of how the engine counts ticks: an animation of N frames occupies exactly N ticks, and the tick where it completes draws nothing — Battle_ReadAnimation returns COMPLETE before rebuilding the geometry, the sequence VM runs in that same tick, reaches the op code of the next part, and pre_Battle_ReadAnimation displays its frame 0. Part 1’s last frame and part 2’s first frame are therefore consecutive ticks, exactly as they would be inside a single animation.

The original animation keeps the first part and the other parts are appended at the end of the section, so existing animation ids stay valid. A bare op code names the animation directly, so ids stop at 0x7F.

Rewriting the sequences

Played by Rewritable Why
a bare op code (XX) yes → XX Z1 Z2 The op code pauses the sequence until the animation ends, so the parts play in a row
A0 XX no A0 does not pause the sequence: A0 XX A0 Z1 replaces part 1 with part 2 on the same frame

Inserting bytes moves every following op code, so every relative jump of the sequence has to be recomputed. Gerogero’s idle loop shows both:

before:  A3 00 E6 FF        E6 FF jumps -1, onto the op code playing animation 0
after:   A3 00 0C E6 FE     animation 0 then 12, and the jump becomes -2 to cover both

Two vanilla sequences (c0m005 seq 12, c0m060 seq 3) jump to their own end, i.e. into the next sequence: their size cannot change, so they are refused too.

Why A0 cannot be chained

A0 exists precisely because the sequence keeps running while the animation plays. Geezard’s attack (c0m004 sequence 12):

A0 0F     play animation 15 (100 frames) without pausing
B9 5F     wait 94 frames
C1 05 ..  rotation loop, one A1 (yield) per frame
E7 D5     jump back while the counter is not 0
A2        end of sequence

The rotation choreography runs in parallel with the animation, and the wait is tuned to the animation length (94 ≈ 100 frames). Chaining a second part would mean starting it at the exact frame part 1 ends, i.e. in the middle of that wait/rotation loop — the timing is hand-written, so it is left to the modder.

Which monsters do not fit

Counts over the 199 readable c0m files (4779 animations):

Target Animations over their limit Splittable Refused Monsters affected
30 fps 7 4 3 7
60 fps 117 53 64 85

60 fps is where the limits bite: most refusals are idle stances looped by A0 that go over the 128 frame Slow limit. 30 fps converts the whole roster with 7 exceptions.

Reading the table: 27 (140f→3) means animation 27, 140 frames, needs 3 parts. 15 (100f, A0) means animation 15, 100 frames, refused because a sequence plays it with A0 (jump = a sequence jumping outside itself, size = cannot be cut small enough). Monsters absent from the table convert as-is at both frame rates.

File Monster 30 fps split 30 fps refused 60 fps split 60 fps refused
c0m004 Geezard — — — 15 (100f, A0)
c0m005 Belhelmel — — — 0 (35f, A0), 33 (33f, jump)
c0m009 Mesmerize — — — 0 (36f, A0)
c0m010 Buel — — — 0 (60f, A0)
c0m013 Snow Lion — — — 0 (47f, A0), 11 (68f, A0)
c0m014 Anacondaur — — — 0 (60f, A0)
c0m016 Cockatrice — — — 0 (39f, A0)
c0m017 Caterchipillar — — 0 (40f→2) —
c0m020 Fastitocalon — — — 22 (35f, A0)
c0m021 Fastitocalon — — — 18 (35f, A0)
c0m024 Hexadragon — — — 26 (82f, A0)
c0m025 Blood Soul — — — 0 (33f, A0)
c0m027 Armadodo — — 0 (49f→2) —
c0m029 Jelleye — — 17 (72f→2) 0 (36f, A0)
c0m030 Tri-Point — — — 0 (40f, A0)
c0m033 Gayla — — — 0 (60f, A0)
c0m034 Gerogero 0 (70f→2) — 0 (70f→3), 3 (88f→2) —
c0m035 Death Claw — — 0 (38f→2) —
c0m037 Grand Mantis — — 0 (40f→2) —
c0m038 Krysta — — 0 (40f→2) —
c0m041 Blue Dragon — — 0 (33f→2) —
c0m043 Bomb — — — 0 (38f, A0)
c0m045 Ochu — — 9 (66f→2) —
c0m046 Adamantoise — — 0 (40f→2) —
c0m047 Chimera — — 21 (69f→2) 0 (40f, A0)
c0m049 Iron Giant — — — 0 (38f, A0)
c0m050 Behemoth — — — 0 (44f, A0)
c0m052 Ruby Dragon — — 0 (36f→2) —
c0m056 Tonberry — — 12 (116f→2) —
c0m057 Torama — — — 0 (41f, A0), 7 (41f, A0)
c0m058 Funguar — — 0 (36f→2) —
c0m060 PuPu — 9 (65f, jump) — 2 (36f, A0), 9 (65f, jump)
c0m061 Ifrit — — — 0 (47f, A0)
c0m062 Minotaur — — — 0 (45f, A0)
c0m063 Sacred — — — 0 (35f, A0)
c0m067 Bahamut — — 9 (78f→2) 0 (46f, A0)
c0m071 G-Soldier — — — 0 (35f, A0)
c0m073 Wedge — — — 0 (35f, A0)
c0m075 Fake President — — 3 (53f→2) —
c0m076 Guard — — — 0 (35f, A0)
c0m077 NORG — 3 (89f, A0) 9 (75f→2), 10 (75f→2), 11 (80f→2), 12 (80f→2) 0 (50f, A0), 3 (89f, A0)
c0m082 Gunblade — — 2 (60f→2), 49 (42f→2) —
c0m083 Tonberry King — 20 (116f, A0) — 20 (116f, A0)
c0m084 Jumbo Cactuar — — 16 (106f→2) 3 (66f, A0)
c0m087 Seifer — — 2 (60f→2) —
c0m088 Edea — — — 0 (35f, A0)
c0m089 Propagator — — 0 (37f→2) —
c0m090 Ultima Weapon — — 26 (107f→2) —
c0m091 Elvoret 27 (140f→2) — 25 (104f→2), 27 (140f→3) 0 (50f, A0), 26 (40f, A0)
c0m092 X-ATM092 0 (69f→2) — 0 (69f→3) —
c0m093 Iguion — — 20 (69f→2) —
c0m094 Gargantua — — 0 (45f→2), 26 (108f→2) —
c0m097 Propagator — — 0 (37f→2) —
c0m098 Propagator — — 0 (37f→2) —
c0m099 Oilboyle — — — 0 (40f, A0)
c0m100 Edea — — — 0 (35f, A0)
c0m101 BGH251F2 — — — 0 (40f, A0)
c0m102 BGH251F2 — — 0 (40f→2) —
c0m108 Paratrooper — — — 0 (35f, A0)
c0m110 Droma — — — 0 (40f, A0)
c0m111 Propagator — — 0 (37f→2) —
c0m112 Adel — — 18 (100f→2) 0 (36f, A0), 10 (35f, A0)
c0m113 {Rinoa} — — 18 (100f→2) 0 (36f, A0), 10 (35f, A0)
c0m114 Omega Weapon — — 26 (107f→2), 32 (128f→2) —
c0m115 “Sorceress” — — — 0 (35f, A0), 9 (64f, A0)
c0m116 “Sorceress” — — — 0 (38f, A0)
c0m117 “Sorceress” — — 13 (110f→2) 0 (35f, A0), 10 (81f, A0)
c0m120 Raijin — — — 0 (33f, A0)
c0m121 Ultimecia — — — 0 (42f, A0), 10 (108f, A0)
c0m122 {Griever} — — 17 (88f→2) —
c0m124 Ultimecia — — 21 (43f→2) —
c0m126 Ultimecia — — — 0 (40f, A0)
c0m128 Seifer — — 25 (42f→2) —
c0m130 Red Giant — — 0 (38f→2) —
c0m131 Elnoyle 27 (140f→2) — 25 (104f→2), 27 (140f→3) 0 (50f, A0)
c0m132 Tiamat — — 0 (46f→2), 9 (78f→2) 17 (34f, A0)
c0m133 Catoblepas — — 0 (44f→2) —
c0m134 Wedge — — 0 (35f→2) —
c0m137 Raijin — — — 0 (33f, A0)
c0m138 UFO? — — — 0 (40f, A0)
c0m139 UFO? — — — 0 (40f, A0)
c0m140 UFO? — — — 0 (40f, A0)
c0m141 UFO? — — — 0 (40f, A0)
c0m142 Gunblade — — 2 (60f→2) —
c0m143 Base Soldier — — — 0 (35f, A0)

Function and data addresses

Name Address Description
pre_Battle_ReadAnimation 0x509440 Animation start; total_frames = 2n-1 in a byte when SLOW (0x509482)
Battle_ReadAnimation 0x508F90 Per-call delta reader; returns COMPLETE at current_frame >= total_frames
Battle_QueueAnimation 0x509520 Applies Slow/Haste only when currentAnimSeqId == basedAnimSeq
AnimSeq_DispatchActionOpcode 0x504BB0 Sequence op codes: bare < 0x80 pauses, A0 does not, A3 sets the base sequence