beginTransparencyGroup
open fun beginTransparencyGroup(bbox: <Error class: unknown class>, ctm: <Error class: unknown class>, isolated: Boolean, knockout: Boolean, alpha: Double, blendMode: <Error class: unknown class>)
Transparency groups: open a Compose saveLayer on the active Canvas with a Paint that carries the requested alpha + blend mode. Subsequent draws accumulate into the offscreen layer; matching endTransparencyGroup calls restore, which composites the layer onto the parent.