1import SwiftUI
2import Photos
3
4/// Renders a progress indicator if we're waiting for the image to load.
5///
6/// This is for when Photos is taking a while to load the high-quality version
7/// of a photo; see the comment on `PHAssetImage`.
8struct LoadingIndicatorOverlay: ViewModifier {
9    let isLoading: Bool
10    
11    func body(content: Content) -> some View {
12        if (isLoading) {
13            content.overlay(alignment: Alignment(horizontal: .trailing, vertical: .bottom)) {
14                
15                // `ProgressView` does have a `tint` modifier, but that doesn't seem to
16                // work on macOS 13 -- this uses some code from a Stack Overflow answer
17                // by aheze: https://stackoverflow.com/a/66568704/1558022
18                ProgressView()
19                    .colorInvert()
20                    .brightness(1)
21                    .padding()
22                    .deferredRendering(
23                        // Note: even if the image is already cached locally, the
24                        // image caching manager typically sends two images: a low-res
25                        // version comes immediately, then a higher-res version within
26                        // a second or two.  This causes the progress indicator to
27                        // "flash" -- it appears then almost instantly disappears.
28                        //
29                        // Deferring the rendering slightly avoids this "flash".
30                        for: .milliseconds(100)
31                    )
32            }
33        } else {
34            content
35        }
36    }
37}
38
39extension View {
40    func loadingIndicator(isLoading: Bool) -> some View {
41        modifier(LoadingIndicatorOverlay(isLoading: isLoading))
42    }
43}