[css-transforms-2] Is addition/accumulation for the Individual Transform Properties specified anywhere?

[stephenmcgruer]

Not sure if I'm just going blind, but reading https://drafts.csswg.org/css-transforms-2/#individual-transforms I can't see a definition of the additive or accumulative composite behavior for the individual properties ('scale', 'translate', 'rotate')? There's a section for transform-list, but that isn't relevant (afaict) for the individual properties.

I've attempted to reverse-engineer it from the WPT test but it isn't always clear. E.g. it seems reasonably clear that 'scale' has an additive behavior of multiply, but it's accumulative behavior isn't clear from the examples.

cc @birtles

[ewilligers]

Hopefully the following is useful:

Suppose we have an addition/accumulation example using only translate3d() or only scale3d() or only rotate3d(). We should be able to map that to an equivalent example that only uses translate or rotate or scale.

So, to determine the appropriate behavior for an example using only scale, we can convert the example to an equivalent example using scale3d(), determine the behavior, and convert that result back to scale.

Wording in the spec could be added to formalize this.

[stephenmcgruer]

That makes sense to me. It can be simplified in implementation, but probably we should just talk in theory for the spec.

It would be very good to have this formalized in the spec. @kevers-google