BaseEmojiLabel improvements

Avoid rechecking disk/memory caches when fetching

Use UIImage thumbnail API, rather than UIGraphicsImageRenderer, and make
thumbnail off main thread when possible

Tusker/Caching/ImageCache.swift

@@ -37,6 +37,11 @@ class ImageCache {
             completion?(entry.data, entry.image)
             return nil
         } else {
+            return getFromSource(url, completion: completion)
+        }
+    }
+    
+    func getFromSource(_ url: URL, completion: ((Data?, UIImage?) -> Void)?) -> Request? {
         return Task.detached(priority: .userInitiated) {
             let result = await self.fetch(url: url)
             switch result {
@@ -49,7 +54,6 @@ class ImageCache {
             }
         }
     }
-    }
     
     func get(_ url: URL, loadOriginal: Bool = false) async -> (Data?, UIImage?) {
         if !ImageCache.disableCaching,

Tusker/Extensions/NSTextAttachment+Emoji.swift

@@ -10,6 +10,7 @@ import UIKit
 
 extension NSTextAttachment {
     // Based on https://github.com/ReticentJohn/Amaroq/blob/7c5b7088eb9fd1611dcb0f47d43bf8df093e142c/DireFloof/InlineImageHelpers.m
+    @available(iOS, deprecated: 15.0)
     convenience init(emojiImage image: UIImage, in font: UIFont, with textColor: UIColor = .label) {
         let adjustedCapHeight = font.capHeight - 1
         var imageSizeMatchingFontSize = CGSize(width: image.size.width * (adjustedCapHeight / image.size.height), height: adjustedCapHeight)

Tusker/Views/BaseEmojiLabel.swift

@@ -40,6 +40,16 @@ extension BaseEmojiLabel {
             return
         }
         
+        // Based on https://github.com/ReticentJohn/Amaroq/blob/7c5b7088eb9fd1611dcb0f47d43bf8df093e142c/DireFloof/InlineImageHelpers.m
+        let adjustedCapHeight = emojiFont.capHeight - 1
+        func emojiImageSize(_ image: UIImage) -> CGSize {
+            var imageSizeMatchingFontSize = CGSize(width: image.size.width * (adjustedCapHeight / image.size.height), height: adjustedCapHeight)
+            var scale: CGFloat = 1.4
+            scale *= UIScreen.main.scale
+            imageSizeMatchingFontSize = CGSize(width: imageSizeMatchingFontSize.width * scale, height: imageSizeMatchingFontSize.height * scale)
+            return imageSizeMatchingFontSize
+        }
+        
         let emojiImages = MultiThreadDictionary<String, UIImage>()
         var foundEmojis = false
         
@@ -57,22 +67,36 @@ extension BaseEmojiLabel {
             foundEmojis = true
             
             if let image = ImageCache.emojis.get(URL(emoji.url)!)?.image {
-                // if the image is cached, add it immediately
-                emojiImages[emoji.shortcode] = image
+                // if the image is cached, add it immediately.
+                // we generate the thumbnail on the main thread, because it's usually fast enough
+                // and the delay caused by doing it asynchronously looks works.
+                // todo: consider caching these somewhere? the cache needs to take into account both the url and the font size, which may vary across labels, so can't just use ImageCache
+                if let thumbnail = image.preparingThumbnail(of: emojiImageSize(image)),
+                   let cgImage = thumbnail.cgImage {
+                    // the thumbnail API takes a pixel size and returns an image with scale 1, but we want the actual screen scale, so convert
+                    // see FB12187798
+                    emojiImages[emoji.shortcode] = UIImage(cgImage: cgImage, scale: UIScreen.main.scale, orientation: .up)
+                }
             } else {
                 // otherwise, perform the network request
                 
                 group.enter()
-                // todo: ImageCache.emojis.get here will re-check the memory and disk caches, there should be another method to force-refetch
-                let request = ImageCache.emojis.get(URL(emoji.url)!) { (_, image) in
-                    guard let image = image,
-                          let transformedImage = ImageGrayscalifier.convertIfNecessary(url: URL(emoji.url)!, image: image) else {
+                let request = ImageCache.emojis.getFromSource(URL(emoji.url)!) { (_, image) in
+                    guard let image else {
+                        group.leave()
+                        return
+                    }
+                    image.prepareThumbnail(of: emojiImageSize(image)) { thumbnail in
+                        guard let thumbnail = thumbnail?.cgImage,
+                              case let rescaled = UIImage(cgImage: thumbnail, scale: UIScreen.main.scale, orientation: .up),
+                              let transformedImage = ImageGrayscalifier.convertIfNecessary(url: URL(emoji.url)!, image: rescaled) else {
                             group.leave()
                             return
                         }
                         emojiImages[emoji.shortcode] = transformedImage
                         group.leave()
                     }
+                }
                 if let request = request {
                     emojiRequests.append(request)
                 }
@@ -91,10 +115,8 @@ extension BaseEmojiLabel {
             // even though the closures is invoked on the same thread that withLock is called, so it's unclear why it needs to be @Sendable (FB11494878)
             // so, just ignore the warnings
             let emojiAttachments = emojiImages.withLock {
-                let emojiFont = self.emojiFont
-                let emojiTextColor = self.emojiTextColor
                 return $0.mapValues { image in
-                    NSTextAttachment(emojiImage: image, in: emojiFont, with: emojiTextColor)
+                    NSTextAttachment(image: image)
                 }
             }
             let placeholder = usePlaceholders ? NSTextAttachment(emojiPlaceholderIn: self.emojiFont) : nil