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Added support to encode APNG instead of GIF, when no animated image format provided by dreampiggy · Pull Request #3867 · SDWebImage/SDWebImage

178-197: ⚠️ Potential issue | 🔴 Critical

Bug: format variable is declared but never used — animated frames always encoded as GIF.

Lines 178–183 compute format based on OS version (PNG for iOS 12+ / macOS 10.14+, GIF otherwise), but line 184 ignores it and hardcodes SDImageFormatGIF:

CFStringRef imageUTType = [NSData sd_UTTypeFromImageFormat:SDImageFormatGIF]; // always GIF

Additionally, line 196 uses GIF-specific property keys (kCGImagePropertyGIFDictionary / kCGImagePropertyGIFDelayTime) regardless of the format. For APNG, these should use the PNG-specific equivalents nested inside kCGImagePropertyPNGDictionary (e.g., kCGImagePropertyAPNGDelayTime).

As a result, animatedImageWithFrames: always produces GIF data regardless of OS version, defeating the purpose of this PR.

🐛 Proposed fix 
     SDImageFormat format;
     if (`@available`(iOS 12.0, tvOS 12.0, macOS 10.14, watchOS 5.0, *)) {
         format = SDImageFormatPNG;
     } else {
         format = SDImageFormatGIF;
     }
-    CFStringRef imageUTType = [NSData sd_UTTypeFromImageFormat:SDImageFormatGIF];
-    // Create an image destination. GIF does not support EXIF image orientation
+    CFStringRef imageUTType = [NSData sd_UTTypeFromImageFormat:format];
+    // Create an image destination. GIF/APNG does not support EXIF image orientation
     CGImageDestinationRef imageDestination = CGImageDestinationCreateWithData((__bridge CFMutableDataRef)imageData, imageUTType, frameCount, NULL);
     if (!imageDestination) {
         // Handle failure.
         return nil;
     }
     
     for (size_t i = 0; i < frameCount; i++) {
         SDImageFrame *frame = frames[i];
         NSTimeInterval frameDuration = frame.duration;
         CGImageRef frameImageRef = frame.image.CGImage;
-        NSDictionary *frameProperties = @{(__bridge NSString *)kCGImagePropertyGIFDictionary : @{(__bridge NSString *)kCGImagePropertyGIFDelayTime : @(frameDuration)}};
+        NSDictionary *frameProperties;
+        if (format == SDImageFormatPNG) {
+            frameProperties = @{(__bridge NSString *)kCGImagePropertyPNGDictionary : @{(__bridge NSString *)kCGImagePropertyAPNGDelayTime : @(frameDuration)}};
+        } else {
+            frameProperties = @{(__bridge NSString *)kCGImagePropertyGIFDictionary : @{(__bridge NSString *)kCGImagePropertyGIFDelayTime : @(frameDuration)}};
+        }
         CGImageDestinationAddImage(imageDestination, frameImageRef, (__bridge CFDictionaryRef)frameProperties);
     }