SwiftUI modifiers compose in the same order as Core Graphics transforms, read from the other end, and offset snaps to the pixel grid so a later scale multiplies its rounding, measured by rendering eight modifier chains against closed-form matrix math
How I prove a from-scratch SwiftUI engine is correct by holding it against real SwiftUI in 125 differential tests, with the actual code, the harness, the firewall, and the floating-point floor that makes agreement mean identical
SwiftUI is the thin graph sitting above 40+ years of engineering. Measured against the real framework and read against Apple's own patent, it is a single demand-driven graph, and the least remarkable engine in the stack it rests on. Here is SwiftUI laid bare, with a hint of the far more interesting machines underneath.