Render blur hashes in conversation view.

Signal/src/ViewControllers/ConversationView/Cells/ConversationMediaView.swift

@@ -121,6 +121,7 @@ public class ConversationMediaView: UIView {
         AssertIsOnMainThread()
 
         guard let attachmentStream = attachment as? TSAttachmentStream else {
+            tryToConfigureForBlurHash(attachment: attachment)
             addDownloadProgressIfNecessary()
             return
         }
@@ -185,6 +186,59 @@ public class ConversationMediaView: UIView {
         return true
     }
 
+    private func tryToConfigureForBlurHash(attachment: TSAttachment) {
+        guard let pointer = attachment as? TSAttachmentPointer else {
+            owsFailDebug("Invalid attachment.")
+            return
+        }
+        guard let blurHash = pointer.blurHash,
+            blurHash.count > 0 else {
+                return
+        }
+        let cacheKey = blurHash
+        let stillImageView = UIImageView()
+        // We need to specify a contentMode since the size of the image
+        // might not match the aspect ratio of the view.
+        stillImageView.contentMode = .scaleAspectFill
+        // Use trilinear filters for better scaling quality at
+        // some performance cost.
+        stillImageView.layer.minificationFilter = .trilinear
+        stillImageView.layer.magnificationFilter = .trilinear
+        stillImageView.backgroundColor = Theme.washColor
+        addSubview(stillImageView)
+        stillImageView.autoPinEdgesToSuperviewEdges()
+        loadBlock = { [weak self] in
+            AssertIsOnMainThread()
+
+            if stillImageView.image != nil {
+                owsFailDebug("Unexpectedly already loaded.")
+                return
+            }
+            self?.tryToLoadMedia(loadMediaBlock: { () -> AnyObject? in
+                guard let image = BlurHash.image(for: blurHash) else {
+                    Logger.warn("Missing image for blurHash.")
+                    return nil
+                }
+                return image
+            },
+                                 applyMediaBlock: { (media) in
+                                    AssertIsOnMainThread()
+
+                                    guard let image = media as? UIImage else {
+                                        owsFailDebug("Media has unexpected type: \(type(of: media))")
+                                        return
+                                    }
+                                    stillImageView.image = image
+            },
+                                 cacheKey: cacheKey)
+        }
+        unloadBlock = {
+            AssertIsOnMainThread()
+
+            stillImageView.image = nil
+        }
+    }
+
     private func configureForAnimatedImage(attachmentStream: TSAttachmentStream) {
         let cacheKey = attachmentStream.uniqueId
         let animatedImageView = YYAnimatedImageView()

SignalServiceKit/src/Messages/Attachments/BlurHash.swift

@@ -84,4 +84,23 @@ public class BlurHash: NSObject {
 
         return promise
     }
+
+    @objc(imageForBlurHash:)
+    public class func image(for blurHash: String) -> UIImage? {
+        // A small thumbnail size will suffice.
+        //
+        // We use a slightly smaller size than we need to
+        // to future-proof this in case we decide to improve
+        // the quality in a future release.
+        //
+        // We could extract the content size from the
+        // blurHash, but it doesn't seem worth the trouble.
+        let thumbnailDimension: CGFloat = 16
+        let thumbnailSize = CGSize(width: thumbnailDimension, height: thumbnailDimension)
+        guard let image = UIImage(blurHash: blurHash, size: thumbnailSize) else {
+            owsFailDebug("Couldn't generate image for blurHash.")
+            return nil
+        }
+        return image
+    }
 }