A standalone, stateless, dual quaternion based skeletal animation system built with interactive applications in mind
WebGL Skeletal Animation Tutorial
skeletal-animation-system aims to give the user a flexible module for managing skeletal animations across different 3d models and bone groups.
skeletal-animation-system aims to provide a sane API for starting, stopping and interpolating skeletal animations.
It supports blending between your previous and current animation when you switch animations. It also supports splitting your model into different bone groups such as the upper and lower body, allowing you to, for example, play a walking animation for your legs while playing a punch animation for your upper body.
skeletal-animation-system does not maintain an internal state, but instead lets the modules consumer track things such as the current animation and the current clock time.
This API is still experimental and will evolve as we use it and realize the kinks.
$ npm install --save skeletal-animation-systemTo run the demo locally:
$ git clone https://github.com/chinedufn/skeletal-animation-system
$ cd skeletal-animation-system
$ npm install
$ npm run demoChanges to the demo and src files will now live reload in your browser.
var animationSystem = require('skeletal-animation-system')
// Parsed using collada-dae-parser or some other parser
var parsedColladaModel = require('./parsed-collada-model.json')
// Animation names and the keyframes that they start and end on
// Zero indexed
// ex: [2, 5] means start on the third keyframe and end at the sixth
var animationRanges = {
'idle': [0, 5],
'jump': [5, 8],
'dance': [8, 14],
'left-arm-punch': [14, 17],
'right-arm-punch': [17, 20]
}
// Convert our joint names into their associated joint index number
// This number comes from collada-dae-parser
// (or your compatible parser of choice)
// Will return an array of joint indices such as like [0, 1, 5, 6, 8]
var upperBodyJointNums = [
'spine', 'chest_L', 'chest_R', 'bicep_L', 'bicep_R'
].reduce(function (jointIndices, jointName) {
jointIndices.push(parsedColladaModel.jointNamePositionIndex[jointName])
return jointIndices
}, [])
// Will return an array of joint indices such as [2, 3, 4, 7, 9]
var lowerBodyJointNums = [
'hip', 'thigh_L', 'thigh_R', 'femur_L'
].reduce(function (jointIndices, jointName) {
jointIndices.push(parsedColladaModel.jointNamePositionIndex[jointName])
return jointIndices
}, [])
// Our options for animating our model's upper body
var upperBodyOptions = {
currentTime: 28.24,
keyframes: keyframes,
jointNums: upperBodyJointsNums,
blendFunction: function (dt) {
// Blend animations linearly over 2.5 seconds
return 1 / 2.5 * dt
},
currentAnimation: {
range: animationRanges['left-arm-punch'],
startTime: 25
},
previousAnimation: {
range: animationRanges['right-arm-punch'],
startTime: 24.5
}
}
// Our options for animating our model's lower body
var lowerBodyOptions = {
currentTime: 28.24,
keyframes: keyframes,
jointNums: lowerBodyJointNums,
currentAnimation: {
range: animationRanges['jump']
startTime: 24.3,
noLoop: true
}
}
var interpolatedUpperBodyJoints = animationSystem
.interpolateJoints(upperBodyOptions).joints
var interpolatedLowerBodyJoints = animationSystem
.interpolateJoints(lowerBodyOptions).joints
// You know have your interpolated upper and lower body dual quaternions.
// You can pass these into `load-collada-dae` or any vertex shader that
// works with dual quaternions
// If you're just getting started and you still need matrices you
// can convert these into matrices uses [dual-quat-to-mat4](https://github.com/chinedufn/dual-quat-to-mat4)TODO: Link to collada-dae-parser README
WIP
- Handle rotation quaternion lerp when dot product is < 0
- Implement more from the papers linked in
Referencessection below (whenever we need them) - Add documentation about how to approach playing a sound effect on a keyframe in your game / simulation / program
- Benchmark
Optional
Type: object
// Example overrides
var myOptions = {
// TODO:
}
interpolatedJoints = animationSystem.interpolateJoints(myOptions)Type: Number
Default: 0
The current number of seconds elapsed. If you have an animation an loop, this will typically be the sum of all of your loops time deltas
// Example of tracking current time
var currentTime = 0
function animationLoop (dt) {
currentTime += dt
}Type: Object
Default: {}
TODO: Link to collada-dae-parser README on keyframes for more info, but also put an example here
Type: Array
An array of joint indices that you would like to interpolate.
Say your model has 4 joints. To interpolate the entire model you would pass in [0, 1, 2, 3]. To only interpolate two of the joints you might pass in [0, 2], or any desired combination.
These joint indices are based on the order of the joints in your keyframes
Type: Function
Default: Blend linearly over 0.2 seconds
A function that accepts a time elapsed in seconds
and returns a value between 0 and 1.
This returned value represents the weight of the new animation.
function myBlendFunction (dt) {
// Blend the old animation into the new one linearly over 5 seconds
return 0.2 * dt)
}Type: Object
An object containing parameters for the current animation
If you supply a previous animation your current animation will be
blended in using your blendFunction
var currentAnimation = {
range: [0, 10],
startTime: 10
}Type: Array
The index of the first and last key for your current animation.
For example, if you have five keyframes at 0.2seconds, 0.8s 2.4s 3.9s and 13.8s
A range of [0, 2] would loop between the keyframes at 0.2s , 0.8s and 2.4s
A range of [2, 3] would loop between the keyframes at 2.4s and 3.9s
Type: Number
The time in seconds that your current animation was initiated. This gets compared with
the currentTime in order to interpolate your joint data appropriately.
Type: Boolean
Whether or not your animation should loop. For example, let's say you are 13 seconds into a 4 second animation.
If noLoop === true then you will be playing the frame at the 4th second.
If noLoop === false then you will be playing the frame at the 1st second.
An object containing parameters for the previous animations.
Your previous animation gets blended out using your blendFunction
while your current animation gets blended in.
Type: Object
Type: Array
The index of the first and last key for your previous animation.
Type: Number
The time in seconds that your previous animation was initiated. This is used in order to blend in the current animation.
- Anatomy of a skeletal animation system part 1, part 2 and part 3
- Dual-Quaternions - From Classical Mechanics to Computer Graphics and Beyond
- This taught us to negate one of the dual quaternions if the dot product of the rotation quaternions was less than 0
MIT