ScrollView force unecessary shape redraw - swiftui

Question

I have a complex shape in a view contained in a scroll view. Each time I scroll the view the shape is drawn making the application clumsy and unresponsive.
This a simple test code.
struct TestView: View {
#ObservedObject private var viewModel = MainViewModel()
var body: some View {
VStack {
....
ScrollView(.horizontal) {
SubView()
.stroke()
.frame(minWidth: 700)
}
}
}
}
struct SubView: Shape {
init() {
print("init")
}
func path(in rect: CGRect) -> Path {
dprint("drawing")
let newPath = Path { path in
for _ in 0..<600 {
path.move(to: CGPoint(x: 0, y: 0))
path.addLine(to: CGPoint(x: rect.size.width, y: rect.size.height))
}
}
return newPath
}
}
I tried to change the code in order to cache the path:
struct SubView: Shape {
var cachedPath: Path?
init() {
print("init")
}
func path(in rect: CGRect) -> Path {
dprint("drawing")
if let path = cachedPath {
dprint("cached path")
return path
}
let newPath = Path { path in
for _ in 0..<600 {
path.move(to: CGPoint(x: 0, y: 0))
path.addLine(to: CGPoint(x: rect.size.width, y: rect.size.height))
}
}
cachedPath = newPath // <-- Cannot assign to property: 'self' is immutable
return newPath
}
}
but I get the following error:
Cannot assign to property: 'self' is immutable
How do I avoid the shape to be redrawn each time a scroll it?

Answer 1

I ended up integrating a custom UIView using UIViewRepresentable. It is super fast and scrolling the view doesn't re-launch the draw(_ rect: CGRect).
Sure it's not a pure SwiftUI solution but it's exactly what I need.