Collision File
All GTA3 games (GTA III, Vice City and San Andreas) have separate files for the visual and physical representations of their models. Collision models are often simply an optimized equivalent of the visual model, reduced in poly count and complexity. The game engine uses them for collision and physics calculations. Unlike graphics meshes, they are comprised not only of triangles but also spheres and boxes, for which exist faster and more accurate collision algorithms.
One or more collision models are packaged to a collision file, denoted by the file extension .col.
Each collision model is identified by a name, which must be the same as the model file and the item definition.
Contents
Version Differences
The col format was first introduced with GTA 3, referred to as version 1 here. The game's successor Vice City used exactly the same format.
In the PS2 version of GTA San Andreas, however, a new version was used (version 2), which was later updated for the PC and XBOX releases (version 3).
Feature Matrix
The following matrix is supposed to give an in-depth feature overview of the 4 known versions of the GTA collision file format.
| Feature | Version 1 | Version 2 | Version 3 | Version 4 |
|---|---|---|---|---|
| Supported by games: | ||||
| GTA III | Y | N | N | N |
| GTA Vice City | Y | N | N | N |
| GTA San Andreas (PS2) | Y | Y | N | N |
| GTA San Andreas (PC/XBOX) | Y | Y | Y | Y |
| Geometric shapes: | ||||
| Collision spheres | Y | Y | Y | Y |
| Collision boxes | Y | Y | Y | Y |
| Collision lines | Y | Y | Y | Y |
| Collision cones | N | N | Y | Y |
| Collision mesh | Y | Y | Y | Y |
| Face groups | N | Y | Y | Y |
| Shadow mesh | N | N | Y | Y |
| Miscellaneous: | ||||
| Light intensity: | N | Y | Y | Y |
| Data compression | N | Y | Y | Y |
| Clump collision | N | N | Y | N |
| Four character code | COLL | COL2 | COL3 | COL4 |
Explanation
The main difference between the old version 1 format and the new version 2 and 3 formats is the reduced file size. Faces and vertices are only half as big, shrinking models without spheres and boxes to almost 50%.
Also, face groups have been introduced, which should speed up collision tests for large models, provided they are calculated properly.
Another new feature are the light intensity values, which are a simple but effective way to achieve realtime lighting. You can define a 1 byte lighting value per face, which causes characters and vehicles to change their brightness when they step onto the face. This is used to simulate darkness in places where the sun cannot reach, such as under buildings, etc.
And finally version 3 introduces a shadow mesh, which is used to create projected shadows. They only include the faces you want to cast a shadow (like bridges); spheres and boxes are not possible.
You can mix all formats within one collision file as you wish, just make sure the target game does support all of them (see matrix above).
File Format
As mentioned above, the collision files are containers for one or more collision models. They do not have a header; models are stored linearly without any padding.
So basically, collision files are simply archives of collision models.
Structures
The following data types and structures are used within this article:
- INT8/UINT8 - signed/unsigned 8 bit integer (1 byte)
- INT16/UINT16 - signed/unsigned 16 bit integer (2 byte)
- INT32/UINT32 - signed/unsigned 32 bit integer (4 byte)
- FLOAT - single precision floating point number (4 byte)
- TVector - float[3] (12 byte)
Some complex structures vary between the format versions.
| Structure Name | Version 1 | Version 2/3 |
|---|---|---|
|
radius : float; center : TVector; min, max: TVector; |
min, max: TVector; center : TVector; radius : float; |
|
material : uint8; flag : uint8; brightness : uint8; light : uint8; | |
|
radius : float; center : TVector; surface: TSurface; |
center : TVector; radius : float; surface: TSurface; |
|
min, max: TVector; surface : TSurface; | |
|
(not used) |
min, max: TVector; StartFace, EndFace : uint16; |
|
float[3] |
int16[3] |
|
a, b, c: uint32; surface: TSurface; |
a, b, c : uint16; material: uint8; light : uint8; |
- all boxes are axis-aligned
Header
char {4} - FourCC ("COLL", "COL2" or "COL3")
uint32 {4} - file size from after this value (so 8 byte less)
char {22} - collision model name
short {2} - model id to apply col to (0-19999)
if not valid (i.e. name of target model does
not match), name is used
TBounds {40} - bounding objects, see above
if (Version >= 2) {
uint16 {2} - number of collision spheres
uint16 {2} - number of collision boxes
uint16 {2} - number of collision mesh faces
uint8 {1} - number of collision lines (or cones)
uint8 {1} - unused (padding)
uint32 {4} - flags
uint32 {4} - offset collision spheres
uint32 {4} - offset collision boxes
uint32 {4} - offset collision lines (or cones)
uint32 {4} - offset collision mesh vertices
uint32 {4} - offset collision mesh faces (triangles)
uint32 {4} - offset triangle planes
if (Version >= 3) {
uint32 {4} - number of shadow mesh faces
uint32 {4} - offset shadow mesh vertices
uint32 {4} - offset shadow mesh faces
}
if (Version == 4) {
uint32 {4} - unknown value (unused)
}
}
|
- All offsets in col 2/3/4 format are relative to after the fourcc, so file offset + 4.
- Col 2/3/4 format does not store the number of vertices. Normally you do not need that, since you would just add the vertex index to the offset in your pointer. But if you do need it, scan the faces for the largest index.
Flags:
- 1 - collision uses cones instead of lines (flag forced to false by engine upon loading)
- 2 - not empty (collision model has spheres or boxes or a mesh)
- 8 - has face groups (if not empty)
- 16 - has shadow mesh (col 3)
- apparently other flags are not used
Body
| Version 1 | Version 2/3 |
|---|---|
uint32 {4} - number of col. spheres
TSphere[] {*} - col. sphere array
uint32 {4} - number of unk. data (0)
uint32 {4} - number of col. boxes
TBox[] {*} - col. box array
uint32 {4} - number of col. vertices
TVertex[] {*} - col. mesh vertex array
uint32 {4} - number of col. faces
TFace[] {*} - col. mesh face array
|
TSphere[] {*} - col. sphere array
TBox[] {*} - col. box array
TVertex[] {*} - col. mesh vertex array
char {2} - optional padding
FaceGroup[] {*} - col. mesh face groups
uint32 {4} - number of face groups
TFace[] {*} - col. mesh face array
TVertex[] {*} - shad. mesh vertex array
char {2} - optional padding
TFace[] {*} - shad. mesh face array
|
- The unknown section was presumably planned to hold a set of lines, used for collisions with very thin objects (like railings). But this was never confirmed, nor is it used anywhere.
- The sequence of sections in the col 2/3 format as given above can be observed in every file sample. However, since there are offsets now, you could order them however you want.
- There is no offset to face groups, reading them is optional. To read them, go to the start of the face array, go back 4 byte, read the ammount of groups, and go back 28*GroupCount byte. But check the flag in the header for existance of face groups first.
- The 2 byte padding after the vertex arrays in col 2/3 is used to provide a 4 byte alignment. It is present if the array's length leaves a rest when divided by 4, i.e. (VertexCount*6) mod 4 != 0.
Annotations
Data Compression and Limits
In the col 2/3 format not only face indices take up half as much space (uint16 instead of uint32); also vertex coordinates are now stored as so-called fixed-point numbers.
To convert such an int16 number to a floating point number, simply divide it by 128.0.
But there is one major disadvantage you have to take care of: meshes are limited to dimensions of +/- 255.99 units on each axis. But this should be no problem, since objects bigger than that would defy the whole purpose of the streaming engine, and should never be used.
Face Groups
Faces in large col 2/3 meshes (more than 80 faces) are grouped by location, and get a bounding box. This way collision checks can be limited to a special area of interest, to speed them up significantly.
Some statistics: There is an minimum average of 13.8 faces per group, maximum is 50[1]. On average there are 31.75 faces per group.
^ In the grouping algorithm, a face count of > 50 is the criterion to split a group.
Shadow Mesh
The so-called "shadow mesh" introduced with version 3 is used to cast real-time shadows in GTA SA. Again, to save cpu time these are reduced to significant parts of the object, like bridges on map parts. Very important is that they always have to be closed! If there are holes in your mesh, you will get odd projection errors, with shadow triangles floating around.
Limits
- Number of vertices - 32767
- Number of faces - 32767
- Vertex position - (-256.0; 256.0) on each axis
The game may also crash if there's too many face groups (more than 1k)
SFX and particles
Interacting with different materials can produce different sound and particle effects. The association between SFX and particles with material are all hardcoded.
GTA III
| Value | Material | Gun shell drop[2] | Footstep[3] | Vehicle skidding[4] |
|---|---|---|---|---|
| 0 | hard | 32-36 | 19 | |
| 1 | hard | 32-36 | 19 | |
| 2 | grass | soft | 37-41 | 158 |
| 3 | dirt | soft | 42-46 | 20 |
| 4 | mud | soft | 42-46 | 20 |
| 5 | pavement | hard | 32-36 | 19 |
| 6 | metal | hard | 52-56 | 19 |
| 7 | hard | 32-36 | 19 | |
| 8 | soft | 32-36 | 19 | |
| 9 | metal | hard | 52-56 | 19 |
| 10 | metal | hard | 52-56 | 19 |
| 11 | metal | hard | 52-56 | 19 |
| 12 | metal | hard | 52-56 | 19 |
| 13 | metal | hard | 52-56 | 19 |
| 14 | metal | hard | 52-56 | 19 |
| 15 | metal | hard | 52-56 | 19 |
| 16 | metal | hard | 52-56 | 19 |
| 17 | soft | 32-36 | 19 | |
| 18 | sand | soft | 61-64 | 20 |
| 19 | water | - | 57-60 | 20 |
| 20 | wood | hard | 47-51 | 19 |
| 21 | wood | hard | 47-51 | 19 |
| 22 | wood | hard | 47-51 | 19 |
| 23 | soft | 32-36 | 19 | |
| 24 | hard | 32-36 | 19 | |
| 25 | hedge | soft | 131-135 | 158 |
| 26 | stone | hard | 32-36 | 19 |
| 27 | metal | hard | 52-56 | 19 |
| 28 | metal | hard | 52-56 | 19 |
For III v1.0:
- ^ Array starts at 0x609274. When a character fires a weapon, some weapons produce gun shells that can be seen ejecting from the weapon and falling to the ground. The sound it plays depends on what material the character is standing on. There are three types of landing sounds used: hard, soft, and none. Hard shell drops use SFX 167 and soft ones use SFX 168.
- ^ Array starts at 0x6077EC. Each footstep characters make creates a sound. These values are associated with an entry in the SFX file. The game chooses an SFX to play at random within that range.
- ^ Array starts at 0x607428. Cars can skid across the ground and create a sound. These values are associated with an entry in the SFX file.
Vice City
| Value | Material | Gun shell drop[5] | Footstep[6] | Vehicle skid[7] | Vehicle scrape[8] | Foot dust[9] |
|---|---|---|---|---|---|---|
| 0 | hard | 42-46 | 25 | 144 | ✗ | |
| 1 | hard | 42-46 | 25 | 144 | ✓ | |
| 2 | grass | soft | 496-500 | 154 | 154 | ✗ |
| 3 | dirt | soft | 501-505 | 26 | 26 | ✓ |
| 4 | mud | soft | 501-505 | 26 | 26 | ✗ |
| 5 | pavement | hard | 42-46 | 25 | 144 | ✓ |
| 6 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 7 | glass | hard | 42-46 | 25 | 144 | ✗ |
| 8 | soft | 42-46 | 25 | 144 | ✗ | |
| 9 | metal door | hard | 511-515 | 25 | 144 | ✗ |
| 10 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 11 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 12 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 13 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 14 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 15 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 16 | metal fence | hard | 511-515 | 25 | 144 | ✗ |
| 17 | soft | 42-46 | 25 | - | ✗ | |
| 18 | sand | soft | 520-523 | 26 | 26 | ✓ |
| 19 | water | - | 516 | 26 | 316 | ✗ |
| 20 | wood | hard | 506-510 | 25 | 144 | ✗ |
| 21 | wood box | hard | 506-510 | 25 | 144 | ✗ |
| 22 | wood plank | hard | 506-510 | 25 | 144 | ✗ |
| 23 | tire | soft | 42-46 | 25 | 144 | ✗ |
| 24 | hard | 42-46 | 25 | 144 | ✗ | |
| 25 | hedge | soft | 127-131 | 154 | 154 | ✗ |
| 26 | stone | hard | 42-46 | 25 | 144 | ✗ |
| 27 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 28 | metal | hard | 511-515 | 25 | 144 | ✗ |
| 29 | hard | 42-46 | 25 | 144 | ✗ | |
| 30 | hard | 42-46 | 25 | 144 | ✗ | |
| 31 | bollard | hard | 42-46 | 25 | 144 | ✗ |
| 32 | gate | hard | 42-46 | 25 | 144 | ✗ |
| 33 | sand | soft | 520-523 | 26 | 26 | ✓ |
For VC v1.0:
- ^ Array starts at 0x5DCD0F. When a character fires a weapon, some weapons produce gun shells that can be seen ejecting from the weapon and falling to the ground. The sound it plays depends on what material the character is standing on. There are three types of landing sounds used: hard, soft, and none. Hard shell drops use SFX 156 and soft ones use SFX 157.
- ^ Array starts at 0x6B66B0. Each footstep characters make creates a sound. These values are associated with an entry in the SFX file. The game chooses an SFX to play at random within that range.
- ^ Array starts at 0x6B6D3C. Cars and motorcycles can skid across the ground and create a sound. These values are associated with an entry in the SFX file.
- ^ Function located at 0x5D9960. The function plays an SFX whenever a vehicle scrapes against a collision. Many scraping sounds are heavily altered and do not seem to resemble the SFX at first glance.
- ^ Array starts at 0x692554. Particle 53 (PEDFOOT_DUST) is produced for every footstep the player makes on the appropriate material.
Tools
Version 1 only
- CollMaker [1] by Steve M. (2002)
Very simple tool that creates single model collision files based on text cordinates as input, such as the text .x files. - CollEditor [2] by Steve M. (2003)
The first 3D editor for collision files. Allowed simple modification and management of collision models. Not very user-friendly, though, and not bug-free. - Col IO [3] by Delfi (2004)
Another 3D editor. Unlike CollEditor, this one allowes to drag spheres, boxes and vertices comfortably with the mouse. Mainly suited for vehicles and quite buggy.
All versions
- KAMS [4] by Kam (2005)
A collection of scripts for 3D Studio Max, including one for import/export of collision files. Does not support face groups. - CollEditor II [5] by Steve M. (2005)
And yet another 3D editor, with many features.
See also
GTAForums: What's the use of collision spheres?
WBD-WBN - new format used in GTA IV
