$proceduralbones

$proceduralbones is a QC command available in all Source games. It uses a special definition file (VRD) to tell the engine to automatically animate certain bones procedurally/at runtime.

Usage

$proceduralbones "<file name>.vrd"

Bug:While the quotation marks are optional provided the file has no spaces in its name, the file extension is NOT optional. Code exists in StudioMDL to read an older, unsupported format if the .vrd file extension is excluded.  (tested in: )

Bug:StudioMDL will not throw an error if the file specified does not exist.  (tested in: )

VRD files work similarly to driven keys in Maya, or transform modifiers in Blender. There are two types of procedural bone:

Helper bones, which consist of a number of keyframes (called "triggers") that tell the engine which angles it should look out for, and as the target bone approaches an angle, its trigger will be blended in proportionally.

Aim constraints, which will always point a bone towards a specified attachment point on the model.

Tip:VRD files support C-style comments, tabs, spaces, etc. but do NOT support multi-line comments.

Guides

• This Facepunch guide (backed up on steam) describes the process of crafting a VRD file, using Source Filmmaker.
• This Steam Guide shows how to do this in entirely in Blender, with the help of an addon.

VRD file syntax & parameters

<helper> HelperName HelperParent DriverParent DriverName

Note:This marks the beginning of a new procedural bone, and ends the previous one, making it mutually exclusive with <aimconstraint>.

HelperName - The name of the helper bone being driven

HelperParent - The name of the helper bone's parent

DriverParent - The name of the driver bone's parent

DriverName - The name of the bone that drives this helper (is effectively being "watched" to see what angle it has)

Note:The parent bones must match their respective bones' parents. The compile will fail if they do not match.

May have up to 32 <trigger> definitions, each of which define a pose to blend HelperName towards based on the rotation of DriverName within its AngleOfInfluence.

In short, each <trigger> is a unique pose that HelperName will translate to whenever DriverName approaches the <trigger>'s defined watch angle.

Example:

<helper>   hlp_forearm_L   bip_lowerArm_L   bip_lowerArm_L   bip_hand_L

<aimconstraint> HelperName HelperParent TargetAttachment

Note:This marks the beginning of a new procedural bone, and ends the previous one, making it mutually exclusive with <helper>.

HelperName - The name of the helper bone being driven

HelperParent - The name of the helper bone's parent

TargetAttachment - Then name of the $attachment to always point towards

Causes HelperName to always face TargetAttachment. The angle it faces can be modified with <aimvector>.

Example:

<aimconstraint>   hlp_piston_R   hlp_lowerArm_R   attach_upperArm_piston_R

Bug:The lexer suggests TargetAttachment should also accept a bone, but no code implements this - using a bone here will throw an error.  (tested in: )

Bug:The TargetAttachment will appear to visibly lag behind by one frame depending on how much movement occurs, which will have more or less impact depending on the client's FPS.  (tested in: )

<basepos> <float|X> <float|Y> <float|Z>

Used to declare the starting position of a procedural bone, relative to its parent.

For <helper>, this is not necessarily required, as each <trigger> also includes a location. If specified anyway, all <trigger> locations will become relative to this one.

For <aimconstraint>, this is basically a necessity, as there is no other way to specify where the bone should be.

Example:

<basepos> 15.003496 0.0043543 3.9911634

Tip:To avoid using external tools or scripts, you can find the correct coordinates by first exporting your model in its reference position as an SMD file, then load this file into any text editor of your choosing. Locate the desired bone in the nodes list; to the left of the name will be its ID, used in the skeleton section of this file. Find time 0 (the first and ideally only frame of animation), and look for the bone ID on the left - the three numbers following this ID are the base pose of this bone relative to its parent.

<trigger> AngleOfInfluence DriverRotation_XYZ HelperRotation_XYZ HelperLocation_XYZ

AngleOfInfluence - A single number representing a cone of influence around this trigger (beyond the cone = 0%, center of the cone = 100%)

DriverRotation_XYZ - A 3D vector representing the rotation of the driver bone (relative to its parent) that represents the center of this trigger's cone

HelperRotation_XYZ, HelperLocation_XYZ - A pair of 3D vectors that respectively represent rotation & location of this helper bone as the driver approaches the center of this trigger's cone

Used by <helper> to declare a specific rotation being watched, and the resulting rotation & location of the helper when the watched bone approaches this rotation.

There can be up to 32 <trigger> lines per <helper>, and all rotations are Euler rotations expressed in degrees.

The angle of influence refers to how far the bone must be from this rotation for this <trigger> to have fully faded out; as it approaches DriverRotation_XYZ, the procedural bone will approach HelperRotation_XYZ and HelperLocation_XYZ

Example:

<trigger>   60   -26.5650735797   -14.4773829758   -26.5652454670      -26.5650162839   -14.4773829758   -26.5651881712      0.000000000   0.000000000   0.000000000

Warning:The same trick above works here too, the three numbers after the bone ID and position are the rotation, but the rotations are in RADIANS - convert to degrees before using them in a <trigger>

<aimvector> <float|X> <float|Y> <float|Z>

Used by <aimconstraint> to declare the direction a <aimconstraint> will face as it tracks its TargetAttachment.

This vector is normalized, but does support any arbitrary orientation. Most commonly, bones will face a particular axis.

Example:

<aimvector> 0 0 -1

(causes the bone to face -Z, or Z always faces opposite the TargetAttachment)

<upvector> <float|X> <float|Y> <float|Z>

Used to clarify which axis on the TargetAttachment is considered "up".

Example:

<upvector> 0 1 0

(causes the bone to rotate with the attachment if it rotates along its local Y axis)

<display><float|X> <float|Y> <float|Z> <float|distance>

Used by the Softimage Mod Tool to store the attributes for procedural bone's appearance in Mod Tool's viewport, but has no purpose outside of it.

Example:

<display> -12.64333 4.33348 0.63611 4.45

<rotateaxis> <float|X> <float|Y> <float|Z>

Used to specify a pre-multiplied angle for all <trigger> definitions.

Example:

<rotateaxis> 0.0004010705   -119.9998795417   89.9996375014

Note:This may have been meant to compliment <basepos> in setting a default angle, but no retail game ever uses it.

<jointorient> <float|X> <float|Y> <float|Z>

Used to specify a post-multiplied angle for all <trigger> definitions.

Example:

<jointorient> 56.3101202181   -154.3411936127   16.1020048039

Note:This may have been meant to compliment <basepos> in setting a default angle, but no retail game ever uses it.

Common applications

The forearm of a full Valve biped skeleton. Note the ulna and wrist bones, both of which are "twist" bones that will be procedurally driven by the rotation of the hand bone.

The most common use case of procedural bones is to automatically rotate forearms, upper arms, thighs, and shins of character models. In the diagram to the right, the mesh is weighted to both a twist bone placed in the middle of the forearm (ValveBiped.Bip01_L_Ulna), and a twist bone located on the wrist (ValveBiped.Bip01_L_Wrist). Rather than require the animator to pose the hand, wrist, and ulna all together (which would not animate in the ragdoll anyway), the ulna & wrist are given procedural bone definitions that allow them to automatically rotate with the hand.

Corrective bones

In areas where rotating weighted bones causes a noticeable loss in mesh volume, such as on the exteriors of elbows & knees, a procedural bone can be used to better maintain the volume. By adding a helper in the same position as the elbow/knee and weighting the vertices nearest the apex of the joint to it, the mesh can be made to deform in a way that doesn't noticeably shrink.

In , the Engineer's character model uses a pair of procedural bones to keep his knee pads from deforming poorly when his knees bend, by watching the angle of the knee & rotating about half the distance to both keep the knee pads in the correct orientation and avoid visible shrinking.

Corrective flexes

In some engine branches^† that support $boneflexdriver, it is possible to use procedural bones to automatically fade in and fade out flexes^‡. This technique lends itself most to applying local corrective or limited delta mush shapes to parts of a mesh that experience low-quality deformations, typically when put into extreme poses. Care must be taken when using this technique, since each corrective flex takes up a flexcontroller slot and requires a corresponding bone in the model's skeleton to drive it. This can quickly add up, counting against the MDL flexcontroller limit (usually 96 or 128) and bone limit (usually 128) and reducing the number of normal flexes and bones available to the model.

Note:^† Deviates from official spec, but tested and working in: , , , ,

Warning:^‡ With additional requirements. Refer to section Driving Flexes with Procedural Bones at the end of this article.

Self-collision approximation

Procedural bones can simulate a quick and dirty approximation of collision between a model's parts. For example, consider a human model wearing a suit jacket. The hem of the jacket could be simply skinned to the thigh bones, such that the hem bends when the model lifts its knee. Alternatively, the hem could be skinned to a separate bone, and $proceduralbones could be used to tell the hem bone to rotate when the thigh bone rotates. In the latter scenario, the hem still bends when the model lifts its knee, but the animator can now pose the thigh and hem independently, improving the model's versatility. Going a step further, several hem bones can be created on the front, sides, and back of the suit jacket, and $proceduralbones can be used to only move the correct hem bone when the model's thigh moves. This way, when the model lifts its knee, the back hem of the jacket remains stationary, with only the front hem bending. This concept can also be applied to rigid accessories on a deforming model, especially in areas where multiple bones exert influence over the deforming mesh.

Mechanical armatures

It's desirable for a mechanical linkage to always point in the correct direction, say for instance in a piston that connects a lower armature to an upper armature. While you can manually animate this, it will neither work with a ragdoll nor during transitions of different animations. You can either manually define a set of known good frames, or an endpoint that the piston should always point towards.

VRD file examples

HWM Femscout forearm twists

Note:Source Filmmaker was used to set up this VRD file, but you can use any modeling software that supports Source models.

<helper> hlp_forearm_L   bip_lowerArm_L   bip_lowerArm_L   bip_hand_L
<basepos> -0.0003 -4.7578 -0.000685692
<trigger> 90 	-0.140879 -7.0729 0.923253 		2.05439e-06 -0.00011566 -0.0109454 	0 0 0
<trigger> 90 	-157.919 -89.6281 158.827 		0.101044 -61.3622 -0.505184 		0 0 0
<trigger> 90 	-0.905463 81.1157 0.0128013 	-1.79037e-05 49.6029 -0.0109647 	0 0 0

<helper> hlp_forearm_R   bip_lowerArm_R   bip_lowerArm_R   bip_hand_R
<basepos> -0.0502548 4.76207 -0.0109539
<trigger> 90 	-0.116485 -7.07782 0.923253 	-26.1455 -71.739 -60.6497 		0 0 0
<trigger> 90 	-0.288436 72.9621 0.610626 		-72.1773 -44.2586 -20.2743 		0 0 0
<trigger> 90 	-179.149 -81.8242 -179.905 		81.3212 -37.0352 -157.273 		0 0 0

This model with source files is available here on MaxOfS2D's website.

Crossbow string

<aimconstraint>	hlp_bow_L		hlp_bowflex_L	attach_string_L
<basepos>       15.070189000 0.000035000 -5.834238000
<aimvector>		-1 0 0 // Causes hlp_bow_L to face away from attach_string_L on the X axis
<upvector>		0 1 0

<aimconstraint>	hlp_bow_R		hlp_bowflex_R	attach_string_R
<basepos>       15.069914000 0.000015000 -5.834859000
<aimvector>		-1 0 0 // Causes hlp_bow_R to face away from attach_string_R on the X axis
<upvector>		0 1 0

Detailed right wrist created from an SMD animation

<helper>        hlp_wrist_R     bip_lowerArm_R  bip_lowerArm_R  bip_hand_R
<basepos>       8.643163000 -0.000000000 0.000021000
<trigger>       60      0.0001718873    150.0000642864  -90.0000958676  0.0001145916    150.0000642864  -90.0001531634  0.000000000     0.000000000     0.000000000      // time 0
<trigger>       60      0.0001718873    -149.9998923990 -90.0002677549  0.0001145916    -149.9998923990 -90.0003250507  0.000000000     0.000000000     0.000000000      // time 1
<trigger>       60      -52.0251407557  -89.9998666845  -38.2358227960  -48.7844914664  -89.9998666845  -38.7109193998  0.000000000     0.000000000     0.000000000      // time 2
<trigger>       60      -0.0001145916   -29.9999555615  -90.0001531634  -0.0001145916   -29.9999555615  -90.0002104591  0.000000000     0.000000000     0.000000000      // time 3
<trigger>       60      -0.0001145916   30.0001274488   -90.0002104591  -0.0001145916   30.0001274488   -90.0002677549  0.000000000     0.000000000     0.000000000      // time 4
<trigger>       60      153.4350608597  14.4776121589   26.5649016923   164.0022360669  26.1849160826   61.2785237386   -0.209301000    -0.381664000    0.031250000      // time 5
<trigger>       60      -153.4347743808 -14.4773829758  26.5648443966   -171.5899734436 -29.0682115950  68.3158205615   -0.189188000    -0.685485000    -0.609611000     // time 6
<trigger>       60      -89.9999239803  -29.9998982657  -0.0002291831   -90.0125290517  -70.4192059232  0.4019298933    -0.103786000    -0.028785000    -0.800817000     // time 7
<trigger>       60      -26.5650735797  -14.4773829758  -26.5652454670  -10.9441241406  -28.1016317947  -66.4090170193  -0.138767000    0.601700000     -0.401906000     // time 8
<trigger>       60      26.5651308755   14.4776121589   -26.5651881712  14.4604807209   26.7658952869   -68.4830096461  -0.374143000    0.995121000     0.171281000      // time 9
<trigger>       60      26.5651308755   165.5226941678  -26.5651881712  2.8720655397    150.2507333217  -86.7703900722  -0.108041000    0.564029000     -0.252821000     // time 10
<trigger>       60      -26.5651308755  -165.5223503931 -26.5652454670  3.3628038912    -149.6761139490 -92.8659161673  -0.211483000    0.771767000     0.567706000      // time 11
<trigger>       60      -90.0001531634  -149.9998923990 -0.0001145916   -86.2042504748  -94.3424857011  -7.0959104054   -0.224750000    0.172373000     0.564973000      // time 12
<trigger>       60      26.5649589881   -14.4775548631  -153.4351181555 3.6163950113    -29.7311237640  -95.1886297730  -0.084996000    -0.475180000    0.216209000      // time 13
<trigger>       60      -26.5651881712  14.4774402716   -153.4351181555 -5.6986955262   28.7843110076   -111.9647767186 -0.068011000    0.295446000     -0.111653000     // time 14
<trigger>       60      -119.9998795417 29.9999555615   89.9999239803   16.3264896680   144.2979310134  -91.0288988845  0.029360000     -0.468964000    -0.863318000     // time 15
<trigger>       60      -119.9998222460 -30.0000701530  89.9996947971   -158.5945458049 -15.7165760951  87.5142038819   -0.044148000    0.546487000     -0.608450000     // time 16
<trigger>       60      7.7956064648    -89.9998666845  -38.1285650968  30.3528975633   -87.9546938348  -100.1075870357 -0.292867000    0.814450000     -0.029658000     // time 17
<trigger>       60      59.9998538272   -29.9998982657  -90.0001531634  19.9532552154   -29.4507755149  -90.1107913136  -0.195600000    0.410349000     0.696194000      // time 18
<trigger>       60      59.9997965314   30.0000701530   -90.0002104591  19.3298771343   19.5167759671   -88.2561842266  -0.296514000    -0.591582000    0.830669000      // time 19
<trigger>       60      120.0001660206  29.9999555615   89.9999239803   156.9124563099  22.1676797978   88.3612073904   -0.348013000    0.475677000     0.507207000      // time 20
<trigger>       60      120.0002233164  -30.0000701530  89.9996947971   -18.0940644660  -137.9124309783 -92.6856636449  -0.288719000    -0.342254000    0.879168000      // time 21
<trigger>       60      -112.4273255466 -89.9998666845  -38.0887445300  -33.8569355510  -95.9927187426  -78.7788893373  -0.413648000    -0.655860000    -0.128256000     // time 22
<trigger>       60      -60.0000257145  -29.9999555615  -90.0001531634  -21.5571359713  -30.0129617034  -90.0030179523  -0.272500000    -0.344648000    -0.597419000     // time 23
<trigger>       60      -60.0000830103  30.0001274488   -90.0002104591  -19.7873839337  32.3326959286   -89.5132536291  -0.207348000    0.373764000     -0.711022000     // time 24

Miscellaneous

When StudioMDL parses <trigger> lines, all characters after the 10th space-delineated number are ignored. This can be used to place comments at the end of the line, like so:

<trigger> 90  -6.75 1.59 3.18  0 0 0  0 0 0   this text is ignored

For symmetrical models (such as humans) it's very common for left/right bones to have completely different local rotations & locations. As such, copying & pasting the procedural bone data from one side to the other will typically not work.

A procedural bone cannot be controlled by two or more driver bones. However, one driver bone can be re-used multiple times to control more than one procedural bone.

Driving Flexes with Procedural Bones

Using $proceduralbones to automatically drive a $boneflexdriver allows for advanced deformation techniques, such as automatic corrective shapes, but this functionality is not officially supported. As such, retail releases of StudioMDL refuse to compile models that use $boneflexdriver on any bone which is marked as the ProceduralBone in $proceduralbones's VRD file. To fix this, StudioMDL may be directly patched using a hex editor, thus allowing it to skip the early exit and successfully compile the model.

Warning:Modified instances of StudioMDL often produce models that deviate from the format expected by the engine - this may cause issues on specific games or engine branches.

Engine-specific patches

• Source 2013 branch

Includes most games where the model format's header begins with IDST0, including Half-Life 2, Counter-Strike: Source, Portal, Team Fortress 2, and Garry's Mod.

Search for the unique byte sequence 04 74 25 8D 4F, then change the byte 74 to EB.

• Alien Swarm

Search for the unique byte sequence 04 74 25 8B, then change the byte 74 to EB.

• Source Filmmaker

Search for the unique byte sequence 04 74 1C 8B 56 5C, then change the byte 74 to EB.

• Portal 2

Search for the unique byte sequence 04 74 28 8B, then change the byte 74 to EB.

Todo: Determine the patch location for other notable games, including and

Important QC modification

In your model's QC file, you must specify $bonemerge on every bone that you make procedural. Refer to your VRD file, and add $bonemerge line(s) to your QC for the ProceduralBone of every <helper> line. The DriverBones do not need $bonemerge.

The reasoning behind the requirement of the seemingly unrelated $bonemerge flag is not yet fully understood.

Confirmation

Once the model has been compiled, you can test it in HLMV to verify that everything works as intended. The skeletal animation should now be able to drive the desired procedural bone(s), which in turn drive the flexcontroller(s).