Scale images to fit the Markdown view

Author: gonzalezreal

Sources/MarkdownUI/Shared/ImageAttachment.swift

@@ -0,0 +1,57 @@
+#if !os(watchOS)
+
+    #if os(macOS)
+        import AppKit
+    #elseif canImport(UIKit)
+        import UIKit
+    #endif
+
+    final class ImageAttachment: NSTextAttachment {
+        #if os(macOS)
+            override func attachmentBounds(
+                for textContainer: NSTextContainer?,
+                proposedLineFragment lineFrag: NSRect,
+                glyphPosition position: CGPoint,
+                characterIndex charIndex: Int
+            ) -> NSRect {
+                guard let image = self.image else {
+                    return super.attachmentBounds(
+                        for: textContainer,
+                        proposedLineFragment: lineFrag,
+                        glyphPosition: position,
+                        characterIndex: charIndex
+                    )
+                }
+
+                let aspectRatio = image.size.width / image.size.height
+                let width = min(lineFrag.width, image.size.width)
+                let height = width / aspectRatio
+
+                return NSRect(x: 0, y: 0, width: width, height: height)
+            }
+        #else
+            override func attachmentBounds(
+                for textContainer: NSTextContainer?,
+                proposedLineFragment lineFrag: CGRect,
+                glyphPosition position: CGPoint,
+                characterIndex charIndex: Int
+            ) -> CGRect {
+                guard let image = self.image else {
+                    return super.attachmentBounds(
+                        for: textContainer,
+                        proposedLineFragment: lineFrag,
+                        glyphPosition: position,
+                        characterIndex: charIndex
+                    )
+                }
+
+                let aspectRatio = image.size.width / image.size.height
+                let width = min(lineFrag.width, image.size.width)
+                let height = width / aspectRatio
+
+                return CGRect(x: 0, y: 0, width: width, height: height)
+            }
+        #endif
+    }
+
+#endif

Sources/MarkdownUI/Shared/ImageDownloader+TextAttachments.swift

@@ -22,7 +22,7 @@
 
             let textAttachmentPairs = imageURLs.map { url in
                 image(for: url).map { image -> (String, NSTextAttachment) in
-                    let attachment = NSTextAttachment()
+                    let attachment = ImageAttachment()
                     attachment.image = image
 
                     return (url.absoluteString, attachment)