jkunz07 162 Posted September 12, 2016 If I want to transform a velocity vector by a matrix4, do I just multiply it by the transpose(inverse(matrix4))? maybe I need to extract the scale from the matrix and multiply the velocity by that as well? Cross posting from https://www.sidefx.com/forum/topic/45863/ in case more people will see it here Share this post Link to post Share on other sites
MirrorSword 13 Posted September 12, 2016 (edited) Hey, I think you can just turn the velocity into a float4, make sure the last component is zero, and then multiply it by the matrix. (As it says here in the docs). However I'm not a master at matrix math so I might be missing something. edit: re-read the help doc I linked and it said that when transforming a normal you want to multiply it by the inverted transpose of the matrix. but it seems like a velocity would just be transformed as a regular vector. However It would be interesting to know why you do one thing with a vector and another with a normal. edit2: Looks like you use the inverted transpose so that the normals will stay perpendicular to the surface. (as explained here). edit3: I did a test and I'm pretty sure that for a velocity vector you want to use the vector rules and not the normal rules. Edited September 12, 2016 by MirrorSword 2 Share this post Link to post Share on other sites
jkunz07 162 Posted September 13, 2016 Thanks James! Finally had a chance to test it and that does seem to be what I'm after. Share this post Link to post Share on other sites
