ANIM (Metroid Prime)
This article is for the ANIM format used in Metroid Prime. See ANIM (File Format) for the other revisions of this format.
The ANIM format is used in conjunction with CINF + CSKR rigging to animate CMDL meshes.
There are two versions of the ANIM format in Metroid Prime (indicated by the file's first u32 value), one with compressed animations and one with uncompressed ones:
| Version | Description |
|---|---|
| 0x0 | Quaternion Array Format (Uncompressed) |
| 0x2 | Rotation Vector Bitstream Format (Compressed) |
Quaternion Array Format (Uncompressed)
The Quaternion Array Format (0x0) is a less common animation format in Metroid Prime. It only appears in a Ridley intro animation and the rotating pirate data artifact hologram above the Impact Crater, as well as some unused Samus animations.
The format stores uncompressed animations by mapping animation channels to bones and supplying rotations as an array of quaternion (WXYZ) keys. Optionally, translations may be specified for a subset of bones as an array of float3 keys.
Layout
| Offset | Type | Element Count | Name | Notes |
|---|---|---|---|---|
| 0x4 | float | 1 | Duration | Time in seconds that the animation plays for |
| 0x8 | u32 | 1 | Unknown 1 | |
| 0xC | float | 1 | Key Interval | Time in seconds between keys of each bone channel (reciprocal of frame-rate) |
| 0x10 | u32 | 1 | Unknown 2 | |
| 0x14 | u32 | 1 | Key Count | Count of keys for each bone channel (keys are set for every frame of the animation) |
| 0x18 | u32 | 1 | Unknown 3 | |
| 0x1C | u32 | 1 | Rotation Channel Index Count | Count of rotation channel indices in the next array. Always 100. |
| 0x20 | u8 | Rotation Channel Index Count | Rotation Channel Index Array | This table maps each bone to a rotation channel, with the index-position corresponding to a Bone ID in the associated CINF, while the index corresponds to the index of a rotation channel. The value is 0xFF if the bone is not animated by this ANIM. |
| u32 | 1 | Translation Channel Index Count | Count of translation channel indices in the next array. Matches the number of valid rotation channels. | |
| u8 | Translation Channel Index Count | Translation Channel Index Array | This table maps each rotation channel to a translation channel, with the index-position corresponding to an entry in the Rotation Channel Index Array above (disregarding 0xFF entries), while the value corresponds to the index of a translation channel. The value is 0xFF if the bone is not translated by this ANIM. | |
| u32 | 1 | Quaternion Key Count | Count of elements in Quaternion Key Array below | |
| float4 | Quaternion Key Count | Quaternion Key Array | The quaternion keys are interleaved as such (bone-major):
|------------|------------|-----|------------| | bone0/key0 | bone0/key1 | ... | bone0/keyN | | bone1/key0 | bone1/key1 | ... | bone1/keyN | | .......... | .......... | ... | .......... | | boneN/key0 | boneN/key1 | ... | boneN/keyN | |------------|------------|-----|------------| | |
| u32 | 1 | Translation Key Count | Count of elements in Translation Key Array below | |
| float3 | Translation Key Count | Translation Key Array | The translation keys are interleaved the same way as the rotation keys. Any bone channels that were marked 0xFF in the Translation Channel Index Array are skipped. | |
| EVNT | 1 | EVNT Ref | ID for this ANIM's EVNT resource, or 0xFFFFFFFF if no events triggered |
Rotation Vector Bitstream Format (Compressed)
The Rotation Vector Bitstream Format (0x2) is the most widely used animation format in Metroid Prime. The format uses a compressed bitstream to store keys that have been delta encoded and quantized to make for a very compact, compressed animation. The data is processed sequentially to reconstruct the uncompressed bone channel data as quaternions.
In addition to the bitstream quantization, the format includes a bitmap specifying which frames of the animation have keys added. Consequently, the runtime generates missing keys via interpolation (reducing animation size further).
Key Values
When decoding the animation, each bone's rotation (and possibly translation) values are initialized to the Initial * values in the bone channel descriptors. For every frame of every bone channel, the key value in the bitstream is added with the previous key value (to resolve the delta encoding).
Once resolved, rotation components are divided by Rotation Divisor, resulting in an axis-angle rotation vector. This rotation vector is converted to quaternion imaginary components with the W component derived via normalized-difference and a sign-bit packed into the bitstream:
q = π / 2.0 / rotation_divisor X = sin(rx * q) Y = sin(ry * q) Z = sin(rz * q) W = sqrt(MAX((1.0 - (X*X + Y*Y + Z*Z)), 0.0)) W = sign_bit ? -W : W
Translation components are multiplied by Translation Multiplier, yielding world units.
Layout
| Offset | Type | Element Count | Name | Notes |
|---|---|---|---|---|
| 0x4 | u32 | 1 | Scratch Size | Amount of memory that the animation system needs to allocate to process animation |
| 0x8 | EVNT | 1 | EVNT Ref | ID for this ANIM's EVNT resource, or 0xFFFFFFFF if no events triggered |
| 0xC | u32 | 1 | Unknown 1 | Always 0x1 |
| 0x10 | float | 1 | Duration | Time in seconds that the animation plays for |
| 0x14 | float | 1 | Interval | Time in seconds between frames (reciprocal of frame-rate, typically 30-fps) |
| 0x18 | u32 | 1 | Unknown 2 | Always 0x3 |
| 0x1C | u32 | 1 | Unknown 3 | Always 0x0 |
| 0x20 | u32 | 1 | Rotation Divisor | Rotation vectors are divided by this value before being applied |
| 0x20 | float | 1 | Translation Multiplier | Translation vectors are multiplied by this value before being applied |
| 0x24 | u32 | 1 | Bone Channel Count | Count of bone channels present in ANIM |
| 0x28 | 4 | u32 | Unknown 4 | Always 0x1 |
| 0x2C | u32 | 1 | Key Bitmap Length | Number of bits in Key Bitmap |
| 0x30 | u32 | round_up(Key Bitmap Length / 32) | Key Bitmap | Word-packed bitmap. Each word is read from least-significant to most-significant bit. A set bit indicates the frame at the bit's position has keys for each bone channel. If the bit is unset, the keys must be generated via interpolation. |
| u32 | 1 | Bone Channel Count | Count of animated bone channels (matches the previous bone channel count) | |
| u32 | 1 | Bone Channel Descriptor Count | Count of bone channel descriptors in Bone Channel Descriptor Table | |
| Bone Channel Descriptor | Bone Channel Descriptor Count | Bone Channel Descriptor Table | Table describing animated bone channels | |
| u32 | <remainder of file> | Key Bitstream | Word-packed bitstream laid out as described by the descriptor table. The bitstream is unpacked just like Key Bitmap (least-significant to most-significant).
Key values are tightly-packed, quantized integers whose bit-depth is specified by the q_* values in the descriptor table. Each bone-channel key-set starts with a single bit providing the W sign-bit (1 for negative, 0 for positive). The key integers are signed using Two's complement representation. The keys are interleaved as such (key-major): |------------|------------|-----|------------| | bone0/key0 | bone1/key0 | ... | boneN/key0 | | bone0/key1 | bone1/key1 | ... | boneN/key1 | | .......... | .......... | ... | .......... | | bone0/keyN | bone1/keyN | ... | boneN/keyN | |------------|------------|-----|------------| |
Bone Channel Descriptor
| Offset | Type | Name | Notes |
|---|---|---|---|
| 0x0 | u32 | Bone ID | Bone ID in the associated CINF for this bone channel |
| 0x4 | u16 | Rotation Key Count | Number of rotation keys in the bitstream for this bone channel.
If this value is 0, the remaining Rotation fields aren't present |
| 0x6 | s16 | Initial Rotation X | Initial X value of bone's rotation vector |
| 0x8 | u8 | Rotation Bits X | Number of bits allocated to bone's rotation delta X in bitstream |
| 0x9 | s16 | Initial Rotation Y | Initial Y value of bone's rotation vector |
| 0xB | u8 | Rotation Bits Y | Number of bits allocated to bone's rotation delta Y in bitstream |
| 0xC | s16 | Initial Rotation Z | Initial Z value of bone's rotation vector |
| 0xE | u8 | Rotation Bits Z | Number of bits allocated to bone's rotation delta Z in bitstream |
| 0xF | u16 | Translation Key Count | If this bone channel has an animated translation, its value will match Rotation Key Count; otherwise the value will be 0.
If the value is 0, the remaining Translation fields aren't present |
| 0x11 | s16 | Initial Translation X | Initial X value of bone's translation vector |
| 0x13 | u8 | Translation Bits X | Number of bits allocated to bone's translation delta X in bitstream |
| 0x14 | s16 | Initial Translation Y | Initial Y value of bone's translation vector |
| 0x16 | u8 | Translation Bits Y | Number of bits allocated to bone's translation delta Y in bitstream |
| 0x17 | s16 | Translation Delta Z | Initial Z value of bone's translation vector |
| 0x19 | u8 | Translation Bits Z | Number of bits allocated to bone's translation delta Z in bitstream |