i am posting this because i seek an understanding of Apple's cross-platform UI strategy. my background is UIKit, Core Animation, and Chameleon a UIKit workalike for (then) OSX. UIKit evolved and Mac Catalyst came along. what is the positioning of Mac Catalyst? it extends and at the same time it limits AppKit. is it an AppKit extension or is it a UI framework of its own? a Mac Catalyst app is not an AppKit app, or is it? or is it sort-of? then came SwiftUI. does SwiftUI sit on top of UIKit (for iOS) and Mac Catalyst (for macOS) or is it an unrelated technology? more recently i see CoreUI messages in the debugger console. where does that fit in? will future UIKit, AppKit, Mac Catalyst, and SwiftUI all build upon CoreUI? will CoreUI become a public framework like CoreGraphics, CoreAnimation? in the old Apple docs there were block diagram overviews of how the individual frameworks would sit one on top of the other. this is what i am looking for...

is there a way to debug Metal raytracing intersection functions? how is that done? i cannot see the intersection functions in the Xcode shader debugger.

a circle can be exactly represented as a rational quadratic b-spline curve. in the curve raytracing example a simd_float3 type was used for control points. a rational curve, however, requires an additional homogenious control point coordinate w. is this supported? the math is straightforward an it would open great opportunities to efficiently render solid primitives like torus and tube.