animBlendNodeAdditiveRotation Node

https://download.autodesk.com/us/maya/2010help/Nodes/animBlendNodeAdditiveRotation.html

https://help.autodesk.com/cloudhelp/2023/ENU/Maya-Tech-Docs/Nodes/animBlendNodeAdditiveRotation.html

earliest known version: 2010

goal: add two rotations together

notes:

  • maya has a specific type of foating point attribute for rotations (doubleAngle)
  • any connections from a doubleAngle to a plain numeric attribute will result in the creation of an intermediary unitConversion Node, which multiplies pi or its reciprocal of to the attribute depending on connection direction
    • this behaviour is not present when the project or scene has rotation units set to RADIANS

solution 1:

rotation ➡ composeMatrix ➡ multMatrix ➡ decomposeMatrix ➡ rotation

  • prevents unitConversion
  • single-equation behaviour reduces number of nodes in the file (see comparison to solution 2)
  • negative of a rotation requires intermediary inverseMatrix node
  • quaternion in matrix, which means results are of -180 < x < 180
    • if an angle of 270 is needed, this is unfortunately not the way

solution 2:

rotation ➡ animBlendNodeAdditiveRotation ➡ rotation

  • prevents unitConverson
  • subtraction and multiplication handled by weight attributes within
  • single-operation behaviour unfortunately means one node is required between two rotations (i.e. for summing n number of rotations, a triangle(n) of addRotate nodes is needed)
  • allows for component-wise or quaternion-based operation, depending on use case

a use of this node

  • a spline IK solver includes a roll and twist attribute, which spins joints about the curve axis.
    • twisting interpolates all the joints between the start and end
    • if the floatAngle value is limited (e.g. parsed as a quaternion at any point in the evaluation chain) and given to the twist attribute, an intended rotation of 270 will end up being a rotation of -90, which causes the chain to twist the other way

wishlist for maya

  • make separate simple maths nodes for operations on floatAngle
    • i am not sure if there is some underlying thing to the animBlendNode- part of animBlendNodeAdditiveRotation, or it’s really doing what it’s doing just with a really really long name
  • make a matrix node that weighs-up transforms (without scaling up the W-component like how the passMatrix would)
    • currently the blendMatrix node servers this purpose, but is very overkill for its purpose