如何在 SwiftUI 中淡化 SF 符号的顶部或底部边缘？

Question

I'm trying to recreate a visual, that consist of 3 SF Symbols. The image in the middle is 100% solid no fade. I would like to fade top edge of the top most image and fade the bottom edge of the bottom most image.

I am using SF Symbols.

I would like to reproduce the following:

(fade top of image)

IMAGE

IMAGE

IMAGE

(fade bottom of image)

How would I accomplish this?

Answer 1

First, keep in mind that there are usage rules around SF Symbols. It may or may not be allowed to modify them in this way. In particular there is a list of "As-Is" symbols that cannot be used for arbitrary purposes. But that doesn't change much about the answer.

The second thing to note is that SF Symbols are a strange beast between text and images. They often act like text, and they often draw outside their frames . That creates problems. You can fix that by forcing them to be real images as discussed in the linked answer.

 
 
 
  
  let config = UIImage.SymbolConfiguration(scale: .large) let image = Image(uiImage: UIImage(systemName:"star.fill", withConfiguration: config)!)
 
 

In the end, as long as you can get an Image that has the correct frame, the rest of this will work. It doesn't matter that it's a SF Symbol.

Asperi's answer explains how to fix this by using resizable .

let image = Image(systemName: "star.fill").resizable().aspectRatio(contentMode: .fit)

(I've added aspectRatio so it doesn't distort.)

First, define your Gradient. This is how the fade will work, and you can configure it with a set of colors or individual color stops. The only thing that matters here is the opacity.

let fade =  Gradient(colors: [Color.clear, Color.black])

(See Asperi's answer for an example using stops, which give you more control over the fade.)

With that, you can apply this gradient as a mask:

let fade =  Gradient(colors: [Color.clear, Color.black])
let image = Image(systemName: "star.fill")
    .resizable().aspectRatio(contentMode: .fit).frame(height: 48)

struct ContentView: View {
    var body: some View {
        VStack {
            image
                .mask(LinearGradient(gradient: fade, startPoint: .top, endPoint: .bottom))
            image
            image
                .mask(LinearGradient(gradient: fade, startPoint: .bottom, endPoint: .top))
        }
    }
}

This raises issues about sizing. This approach is a flexible stack. It will grow to fill whatever container it's put in. You may want to constrain it a couple of ways.

First, you can decide the height of the entire stack by putting a frame on it:

    VStack {
        image
            .mask(LinearGradient(gradient: fade, startPoint: .top, endPoint: .bottom))
        image
        image
            .mask(LinearGradient(gradient: fade, startPoint: .bottom, endPoint: .top))
    }.frame(height: 128)
     ^^^^^^^^^^^^^^^^^^^

Or you could fix the size of each image instead:

let image = Image(systemName: "star.fill")
    .resizable().aspectRatio(contentMode: .fit).frame(width: 48)
                                               ^^^^^^^^^^^^^^^^^

Answer 2

Here is my alternate (without UIKit usage)

struct TestSFSymbolsFade: View {
    var body: some View {
        VStack {
            Image(systemName: "ant.fill").resizable()
            Image(systemName: "ant.fill").resizable()
            Image(systemName: "ant.fill").resizable()
        }
        .mask(LinearGradient(gradient: Gradient(stops: [
            .init(color: .clear, location: 0),
            .init(color: .black, location: 0.25),
            .init(color: .black, location: 0.75),
            .init(color: .clear, location: 1)
        ]), startPoint: .top, endPoint: .bottom))
        .frame(width: 40, height: 160) // < just for demo, can be any or absent
    }
}

backup