Creature animations¶

This page tracks how creatures advance animation phase and select atlas frames.

See also: Creature pool struct, Atlas notes.

Animation phase (creature_anim_phase / offset 0x94)¶

• creature_anim_phase (float) is advanced in creature_update_all (0x00426220) using the per-type rate stored in the type table (creature_type_table).

• The phase wraps at 31 for the long strip or 15 for the short ping‑pong strip.

• Evidence: analysis/frida/creature_anim_trace_summary.json (captured via scripts/frida/creature_anim_trace.js).

Strip selection and frame mapping¶

The renderer (creature_render_type, 0x00418b60) selects an atlas frame based on:

• the type table base_frame
• the per-creature flags (creature_flags)
• the integer part of anim_phase
• the creature heading (rotation)

Frame selection is checked against 2,640 native PC24 witnesses:

• Flag 0x4 selects the short 8-frame ping‑pong strip.
• Flag 0x40 forces the long strip even when 0x4 is set.

• For the short strip: frame = base + 0x10 + ping_pong(__ftol(phase + 0.5) % 16), where ping‑pong folds 0..15 into 0..7..0. The remainder is signed for diagnostic negative phases; arithmetic before integer conversion follows gameplay PC24 rounding.

• For the long strip (alive, lifecycle_stage >= 16.0): frame = __ftol(anim_phase + 0.5).

• If the type mirror flag is set and frame > 0x0f, the index is mirrored: frame = 0x1f - frame.
• In the shadow/body long-strip passes, flag 0x10 adds +0x20 after either alive or death-stage selection (an alternate strip for some spawns).
• For the long strip during death staging (0 <= lifecycle_stage < 16.0): frame = __ftol((base_frame + 0x0f) - lifecycle_stage)
• This effectively ramps through the 16 death frames as lifecycle_stage decays from ~16 to 0.
• For long-strip corpses (lifecycle_stage < 0.0): frame = base_frame + 0x0f (static corpse frame).
• Rotation: grim_set_rotation(creature_heading - pi/2); creatures visually face along their movement heading.

Shadow/outline pass (shadows_enabled)¶

When crimson.cfg shadows_enabled is enabled (config_shadows_enabled) and the Monster Vision perk is not active, creature_render_type runs an extra pre-pass that darkens behind each creature sprite:

• alpha is derived from creature tint alpha (tint_a * 0.4 in the decompile)
• the sprite is slightly upscaled (~size * 1.07) and offset down-right before the main draw
• for long-strip corpses (lifecycle_stage < 0.0), the shadow alpha decays much faster: tint_a * 0.4 + lifecycle_stage * 0.5 (clamped to >= 0).
• Evidence: analysis/frida/creature_render_trace_summary.json (captured via scripts/frida/creature_render_trace.js).

Each species finishes all shadows before any body, followed by its optional hit flashes. The species order is zombie, spider_sp1, spider_sp2, alien, lizard. Body and flash dimensions use actual creature size; the ports no longer clamp Python bodies to 16–128 pixels or tie their dimensions to atlas resolution. Both ports preserve this ordering, including zero-alpha shadow submissions. See the native pass-order and dimension audit.

Body and shadow colour arithmetic¶

For positive Energizer time and max_health < 500, the body tint blends toward (0.5, 0.5, 1, 1) as (1 - t) * base + t * target, with t capped at 1. A negative lifecycle then adds lifecycle_stage * 0.1 to alpha and clamps the result to zero. Shadow alpha starts at tint_a * 0.4; negative lifecycle adds lifecycle_stage * 0.5 for long strips or * 0.1 for short strips, with the same lower clamp. Transition alpha is multiplied last in both passes.

The ports round each arithmetic operation at gameplay PC24 and pack each channel by truncating channel * 255 and keeping its low byte. Without Energizer or corpse fading, tint (0.8, 0.7, 0.6, 0.9) at transition 0.8 becomes (204, 178, 153, 183). See the native colour audit for exact float words, packed bytes, old-port controls and proof limits.

Hit flash with violence disabled¶

When violence_disabled is nonzero, each species' body batch is followed by a white additive flash batch. Active matching creatures with positive hit_flash_timer emit two identical quads at their actual size. The alpha is min(hit_flash_timer * 5, 1) * transition_alpha, rounded at PC24 after each multiplication. Grim2D truncates alpha * 255 when packing the color. The pass restores normal alpha blending afterward.

The flash uses the same ping-pong frames as the body. For long strips, the shock offset applies only while lifecycle_stage >= 16; dying shock creatures therefore use a different frame in this pass. Stages below -10 are retired by the preceding body pass and do not flash.

creature_apply_damage sets the timer to 0.2f, including zero damage and corpse hits. The active-creature update subtracts frame_dt while the timer is positive, before the Freeze branch, and allows it to cross below zero. Spawn allocation clears it. Both ports implement the flash; Zig also restores the timer from existing replay slot residue. See the native lifetime and draw audit.

Creature flags related to animation / attacks (partial)¶

The creature_flags bitfield is consulted in creature_update_all and related helpers:

• 0x4 — short ping‑pong animation strip.
• 0x10 — ranged attack variant; also selects the +0x20 strip offset in rendering.
• 0x40 — force long animation strip even if 0x4 is set.

Creature type table (creature_type_texture / creature_type_table)¶

Stride: 0x44 bytes (0x11 floats). Indexed by type_id.

data_map now labels the entry bases:

• creature_type_table[0] (zombie) at 0x00482728
• creature_type_lizard at 0x0048276c
• creature_type_alien at 0x004827b0
• creature_type_spider_sp1 at 0x004827f4
• creature_type_spider_sp2 at 0x00482838
• creature_type_trooper at 0x0048287c

Field map (partial):

Known initial entries (from the reset/init routine that loads creature textures):

Notes:

• No references to offsets 0x1c..0x30 were found in the decompiled output. Only offset 0x20 is initialized (to 1.0), so the remaining fields appear unused or reserved in this build.