Separate the image class and coder class's protocol. Make this two more modular

SDWebImage/SDAnimatedImage.h

@@ -7,51 +7,25 @@
  */
 
 #import "SDWebImageCompat.h"
-#import "NSData+ImageContentType.h"
+#import "SDWebImageCoder.h"
 
-@protocol SDWebImageAnimatedCoder;
-@protocol SDAnimatedImage <NSObject>
+
+/**
+ This is the protocol for SDAnimatedImage class only but not for SDWebImageAnimatedCoder. If you want to provide a custom animated image class with full advanced function, you can conform to this instead of the base protocol.
+ */
+@protocol SDAnimatedImage <SDAnimatedImageProvider>
 
 @required
 /**
- The original animated image data for current image. If current image is not an animated format, return nil.
- We may use this method to grab back the original image data if need, such as NSCoding or compare.
+ Initializes the image with an animated coder. You can use the coder to decode the image frame later.
+ @note Normally we use `initWithData:scale:` to create custom animated image class. However, for progressive image decoding, we will use this instead.
  
- @return The animated image data
+ @param animatedCoder An animated coder which conform `SDWebImageAnimatedCoder` protocol
+ @param scale The scale factor to assume when interpreting the image data. Applying a scale factor of 1.0 results in an image whose size matches the pixel-based dimensions of the image. Applying a different scale factor changes the size of the image as reported by the `size` property.
+ @return An initialized object
  */
-- (nullable NSData *)animatedImageData;
+- (nullable instancetype)initWithAnimatedCoder:(nonnull id<SDWebImageAnimatedCoder>)animatedCoder scale:(CGFloat)scale;
 
-/**
- Total animated frame count.
- It the frame count is less than 1, then the methods below will be ignored.
-
- @return Total animated frame count.
- */
-- (NSUInteger)animatedImageFrameCount;
-/**
- Animation loop count, 0 means infinite looping.
-
- @return Animation loop count
- */
-- (NSUInteger)animatedImageLoopCount;
-/**
- Returns the frame image from a specified index.
- @note The index maybe randomly if one image was set to different imageViews, keep it re-entrant. (It's not recommend to store the images into array because it's memory consuming)
-
- @param index Frame index (zero based).
- @return Frame's image
- */
-- (nullable UIImage *)animatedImageFrameAtIndex:(NSUInteger)index;
-/**
- Returns the frames's duration from a specified index.
- @note The index maybe randomly if one image was set to different imageViews, keep it re-entrant. (It's recommend to store the durations into array because it's not memory-consuming)
-
- @param index Frame index (zero based).
- @return Frame's duration
- */
-- (NSTimeInterval)animatedImageDurationAtIndex:(NSUInteger)index;
-
-// These methods are for SDAnimatedImage class only but not for SDWebImageAnimatedCoder.
 @optional
 /**
  Pre-load all animated image frame into memory. Then later frame image request can directly return the frame for index without decoding.
@@ -71,16 +45,6 @@
  */
 - (BOOL)isAllFramesLoaded;
 
-/**
- Initializes the image with an animated coder. You can use the coder to decode the image frame later.
- @note Normally we use `initWithData:scale:` to create custom animated image class. So you can implement your custom class without our built-in coder.
-
- @param animatedCoder An animated coder which conform `SDWebImageAnimatedCoder` protocol
- @param scale The scale factor to assume when interpreting the image data. Applying a scale factor of 1.0 results in an image whose size matches the pixel-based dimensions of the image. Applying a different scale factor changes the size of the image as reported by the `size` property.
- @return An initialized object
- */
-- (nullable instancetype)initWithAnimatedCoder:(nonnull id<SDWebImageAnimatedCoder>)animatedCoder scale:(CGFloat)scale;
-
 @end
 
 @interface SDAnimatedImage : UIImage <SDAnimatedImage>

SDWebImage/SDAnimatedImage.m

@@ -282,9 +282,6 @@ static NSArray *SDBundlePreferredScales() {
     if (!data || data.length == 0) {
         return nil;
     }
-    if (scale <= 0) {
-        scale = 1;
-    }
     data = [data copy]; // avoid mutable data
     id<SDWebImageAnimatedCoder> animatedCoder = nil;
     for (id<SDWebImageCoder>coder in [SDWebImageCodersManager sharedManager].coders) {
@@ -298,24 +295,7 @@ static NSArray *SDBundlePreferredScales() {
     if (!animatedCoder) {
         return nil;
     }
-    UIImage *image = [animatedCoder animatedImageFrameAtIndex:0];
-    if (!image) {
-        return nil;
-    }
-#if SD_MAC
-    self = [super initWithCGImage:image.CGImage size:NSZeroSize];
-#else
-    self = [super initWithCGImage:image.CGImage scale:scale orientation:image.imageOrientation];
-#endif
-    if (self) {
-        _coder = animatedCoder;
-#if SD_MAC
-        _scale = scale;
-#endif
-        SDImageFormat format = [NSData sd_imageFormatForImageData:data];
-        _animatedImageFormat = format;
-    }
-    return self;
+    return [self initWithAnimatedCoder:animatedCoder scale:scale];
 }
 
 - (instancetype)initWithAnimatedCoder:(id<SDWebImageAnimatedCoder>)animatedCoder scale:(CGFloat)scale {

SDWebImage/SDWebImageCoder.h

@@ -9,7 +9,6 @@
 #import <Foundation/Foundation.h>
 #import "SDWebImageCompat.h"
 #import "NSData+ImageContentType.h"
-#import "SDAnimatedImage.h"
 
 typedef NSString * SDWebImageCoderOption NS_STRING_ENUM;
 typedef NSDictionary<SDWebImageCoderOption, id> SDWebImageCoderOptions;
@@ -118,11 +117,56 @@ FOUNDATION_EXPORT SDWebImageCoderOption _Nonnull const SDWebImageCoderEncodeComp
 
 @end
 
+/**
+ This is the animated image protocol to provide the basic function for animated image rendering. It's adopted by `SDAnimatedImage` and `SDWebImageAnimatedCoder`
+ */
+@protocol SDAnimatedImageProvider <NSObject>
+
+@required
+/**
+ The original animated image data for current image. If current image is not an animated format, return nil.
+ We may use this method to grab back the original image data if need, such as NSCoding or compare.
+ 
+ @return The animated image data
+ */
+- (nullable NSData *)animatedImageData;
+
+/**
+ Total animated frame count.
+ It the frame count is less than 1, then the methods below will be ignored.
+ 
+ @return Total animated frame count.
+ */
+- (NSUInteger)animatedImageFrameCount;
+/**
+ Animation loop count, 0 means infinite looping.
+ 
+ @return Animation loop count
+ */
+- (NSUInteger)animatedImageLoopCount;
+/**
+ Returns the frame image from a specified index.
+ @note The index maybe randomly if one image was set to different imageViews, keep it re-entrant. (It's not recommend to store the images into array because it's memory consuming)
+ 
+ @param index Frame index (zero based).
+ @return Frame's image
+ */
+- (nullable UIImage *)animatedImageFrameAtIndex:(NSUInteger)index;
+/**
+ Returns the frames's duration from a specified index.
+ @note The index maybe randomly if one image was set to different imageViews, keep it re-entrant. (It's recommend to store the durations into array because it's not memory-consuming)
+ 
+ @param index Frame index (zero based).
+ @return Frame's duration
+ */
+- (NSTimeInterval)animatedImageDurationAtIndex:(NSUInteger)index;
+
+@end
 
 /**
  This is the animated image coder protocol for custom animated image class like  `SDAnimatedImage`. Through it inherit from `SDWebImageCoder`. We currentlly only use the method `canDecodeFromData:` to detect the proper coder for specify animated image format.
  */
-@protocol SDWebImageAnimatedCoder <SDWebImageCoder, SDAnimatedImage>
+@protocol SDWebImageAnimatedCoder <SDWebImageCoder, SDAnimatedImageProvider>
 
 @required
 /**

SDWebImage/SDWebImageDefine.h

@@ -50,7 +50,7 @@ FOUNDATION_EXPORT SDWebImageContextOption _Nonnull const SDWebImageContextCustom
 FOUNDATION_EXPORT SDWebImageContextOption _Nonnull const SDWebImageContextCustomTransformer;
 
 /**
- A Class object which the instance is a `UIImage/NSImage` subclass and adopt `SDAnimatedImage` protocol. We will call `initWithData:scale:` to create the instance (or `initWithAnimatedCoder:sclae` when using progressive download) . If the instance create failed, fallback to normal `UIImage/NSImage`.
+ A Class object which the instance is a `UIImage/NSImage` subclass and adopt `SDAnimatedImage` protocol. We will call `initWithData:scale:` to create the instance (or `initWithAnimatedCoder:scale` when using progressive download) . If the instance create failed, fallback to normal `UIImage/NSImage`.
  This can be used to improve animated images rendering performance (especially memory usage on big animated images) with `SDAnimatedImageView` (Class).
  */
 FOUNDATION_EXPORT SDWebImageContextOption _Nonnull const SDWebImageContextAnimatedImageClass;

SDWebImage/SDWebImageDownloaderOperation.m

@@ -365,7 +365,7 @@ didReceiveResponse:(NSURLResponse *)response
             UIImage *image;
             if ([self.context valueForKey:SDWebImageContextAnimatedImageClass]) {
                 Class animatedImageClass = [self.context valueForKey:SDWebImageContextAnimatedImageClass];
-                if ([animatedImageClass isSubclassOfClass:[UIImage class]] && [animatedImageClass conformsToProtocol:@protocol(SDAnimatedImage)] && [animatedImageClass instancesRespondToSelector:@selector(initWithAnimatedCoder:scale:)] && [self.progressiveCoder conformsToProtocol:@protocol(SDWebImageAnimatedCoder)]) {
+                if ([animatedImageClass isSubclassOfClass:[UIImage class]] && [animatedImageClass conformsToProtocol:@protocol(SDAnimatedImage)] && [self.progressiveCoder conformsToProtocol:@protocol(SDWebImageAnimatedCoder)]) {
                     CGFloat scale = SDImageScaleForKey(self.cacheKey);
                     image = [[animatedImageClass alloc] initWithAnimatedCoder:(id<SDWebImageAnimatedCoder>)self.progressiveCoder scale:scale];
                 }