SwiftUI Path is pixelated when in second Navigation View

Question

I have a strange behavior on my SwiftUI app. I draw a Path with a linear gradient as stroke color.

This path is displayed like this in my view:

GeometryReader { proxy in
    LinePath(width: proxy.size.width, height: proxy.size.height)
        .stroke(gradient, lineWidth: 3)
}
.frame(height:200)
.padding()

(LinePath struct extends Shape and draw the Path)
When this code is displayed on first view, it draws correctly:

But if I display it in a second view after a NavigationLink, the drawn line is "pixelated":

As it may be difficult to understand and there is quite lot of code (for a web page), I did a demo project you can get here.

To test it, you can open testprojectApp.swift and comment/uncomment parts:

ContentView() // <--- Uncomment this to get the issue
//SubView() // <--- Uncomment this and it works

If you call SubView (where this LinePath is drawn), it works. If you call ContentView that will display a button to navigate to SubView, it draws a pixelated line.

Notes:

If I don't set a height, it is never pixelated (.frame(height:200)).
If I don't use a gradient but a simple color (as .blue), it is never pixelated.

EDIT: I've found a "workaround", to redraw the line 0.01s after it appeared and change its height. It visually "works" but of course it is not a good method...

@State var height: CGFloat = 0
var body: some View {
    
    GeometryReader { proxy in
        LinePath(width: proxy.size.width, height: proxy.size.height)
            .stroke(gradient, lineWidth: 3)
    }
    .frame(height:height)
    .padding()
    .onAppear() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.01) {
            height = 200
        }
    }
}

jnpdx · Accepted Answer · 2021-11-20 21:37:33Z

2

You can add .drawingGroup() and it seems to resolve the issue without having to use the delay:

GeometryReader { proxy in
    LinePath(width: proxy.size.width, height: proxy.size.height)
        .stroke(gradient, lineWidth: 3)
}
.frame(height:200)
.padding()
.drawingGroup() //<-- here

answered Nov 20, 2021 at 21:37

jnpdx

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3 Comments

Jonathan Over a year ago

Yes it works! It's a bit slower to display view but it is not pixelated anymore.

jnpdx Over a year ago

I’m not seeing a speed change at all, but I’m on an M1, so it’s pretty speedy in general.

Jonathan Over a year ago

Sorry, you're right! I was trying on my normal project that has much more data. Thank you for your help.

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