Cache image heights to reduce popping

damus/Util/PreviewCache.swift

@@ -24,12 +24,21 @@ enum Preview {
 }
 
 class PreviewCache {
-    var previews: [String: Preview]
+    private var previews: [String: Preview]
+    private var image_heights: [String: CGFloat]
     
     func lookup(_ evid: String) -> Preview? {
         return previews[evid]
     }
     
+    func lookup_image_height(_ evid: String) -> CGFloat? {
+        return image_heights[evid]
+    }
+    
+    func cache_image_height(evid: String, height: CGFloat) {
+        self.image_heights[evid] = height
+    }
+    
     func store(evid: String, preview: LPLinkMetadata?)  {
         switch preview {
         case .none:
@@ -41,5 +50,6 @@ class PreviewCache {
     
     init() {
         self.previews = [:]
+        self.image_heights = [:]
     }
 }