Add option to scale down large images on iOS

Option is SDWebImageScaleDownLargeImage

SDWebImage/SDWebImageDecoder.h

@@ -15,4 +15,6 @@
 
 + (UIImage *)decodedImageWithImage:(UIImage *)image;
 
++ (UIImage *)decodedAndScaledDownImageWithImage:(UIImage *)image;
+
 @end

SDWebImage/SDWebImageDecoder.m

@@ -10,9 +10,30 @@
 
 #import "SDWebImageDecoder.h"
 
+/*
+ Size in MB, compatible with all iOS devices.
+ */
+#define kSDWebImageDecoderMaxImageSizeMB 4.f
+
+#define SDWebImageDecoderMaxTotalPixels(bitsPerComponent) ((kSDWebImageDecoderMaxImageSizeMB*1024.*1024.*8.)/bitsPerComponent)
+
+inline static CGSize SDWebImageDecoderConstrainedSize(UIImage *image) {
+    CGImageRef imageRef = image.CGImage;
+    CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
+    size_t imageBitsPerComponent = CGImageGetBitsPerComponent(imageRef);
+    CGFloat imageTotalPixels = imageSize.width * imageSize.height;
+    if (imageTotalPixels < SDWebImageDecoderMaxTotalPixels(imageBitsPerComponent)) {
+        return CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX);
+    }
+    CGFloat ratio = SDWebImageDecoderMaxTotalPixels(imageBitsPerComponent) / imageTotalPixels;
+    CGFloat maxWidth = imageSize.width * ratio;
+    CGFloat maxHeight = imageSize.height *ratio;
+    return CGSizeMake(floorf(maxWidth), floorf(maxHeight));
+}
+
 @implementation UIImage (ForceDecode)
 
-+ (UIImage *)decodedImageWithImage:(UIImage *)image {
++ (UIImage *)decodedAndScaledDownImageToSize:(CGSize)size withImage:(UIImage *)image {
     if (image.images) {
         // Do not decode animated images
         return image;
@@ -20,15 +41,20 @@
 
     CGImageRef imageRef = image.CGImage;
     CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
-    CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};
+    
+    if ((size.width < imageSize.width) && (size.height < imageSize.height)) {
+        imageSize = size;
+    }
 
+    CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};
+    
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
     CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
 
     int infoMask = (bitmapInfo & kCGBitmapAlphaInfoMask);
     BOOL anyNonAlpha = (infoMask == kCGImageAlphaNone ||
-            infoMask == kCGImageAlphaNoneSkipFirst ||
-            infoMask == kCGImageAlphaNoneSkipLast);
+                        infoMask == kCGImageAlphaNoneSkipFirst ||
+                        infoMask == kCGImageAlphaNoneSkipLast);
 
     // CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.
     // https://developer.apple.com/library/mac/#qa/qa1037/_index.html
@@ -39,7 +65,7 @@
         // Set noneSkipFirst.
         bitmapInfo |= kCGImageAlphaNoneSkipFirst;
     }
-            // Some PNGs tell us they have alpha but only 3 components. Odd.
+    // Some PNGs tell us they have alpha but only 3 components. Odd.
     else if (!anyNonAlpha && CGColorSpaceGetNumberOfComponents(colorSpace) == 3) {
         // Unset the old alpha info.
         bitmapInfo &= ~kCGBitmapAlphaInfoMask;
@@ -48,17 +74,18 @@
 
     // It calculates the bytes-per-row based on the bitsPerComponent and width arguments.
     CGContextRef context = CGBitmapContextCreate(NULL,
-            imageSize.width,
-            imageSize.height,
-            CGImageGetBitsPerComponent(imageRef),
-            0,
-            colorSpace,
-            bitmapInfo);
+                                                 imageSize.width,
+                                                 imageSize.height,
+                                                 CGImageGetBitsPerComponent(imageRef),
+                                                 0,
+                                                 colorSpace,
+                                                 bitmapInfo);
     CGColorSpaceRelease(colorSpace);
 
     // If failed, return undecompressed image
     if (!context) return image;
 
+    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
     CGContextDrawImage(context, imageRect, imageRef);
     CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
 
@@ -69,4 +96,12 @@
     return decompressedImage;
 }
 
++ (UIImage *)decodedImageWithImage:(UIImage *)image {
+    return [UIImage decodedAndScaledDownImageToSize:CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX) withImage:image];
+}
+
++ (UIImage *)decodedAndScaledDownImageWithImage:(UIImage *)image {
+    return [UIImage decodedAndScaledDownImageToSize:SDWebImageDecoderConstrainedSize(image) withImage:image];
+}
+
 @end

SDWebImage/SDWebImageDownloader.h

@@ -50,7 +50,11 @@ typedef NS_OPTIONS(NSUInteger, SDWebImageDownloaderOptions) {
      */
     SDWebImageDownloaderHighPriority = 1 << 7,
     
-
+    /**
+     * Scale down the image
+     */
+    SDWebImageDownloaderScaleDownLargeImage = 1 << 8,
+    
 };
 
 typedef NS_ENUM(NSInteger, SDWebImageDownloaderExecutionOrder) {

SDWebImage/SDWebImageDownloaderOperation.m

@@ -357,7 +357,15 @@
 
             if (!image.images) // Do not force decod animated GIFs
             {
+#ifdef TARGET_OS_IPHONE
+                if (self.options & SDWebImageDownloaderScaleDownLargeImage) {
+                    image = [UIImage decodedAndScaledDownImageWithImage:image];
+                } else {
+                    image = [UIImage decodedImageWithImage:image];
+                }
+#else
                 image = [UIImage decodedImageWithImage:image];
+#endif
             }
 
             if (CGSizeEqualToSize(image.size, CGSizeZero)) {

SDWebImage/SDWebImageManager.h

@@ -74,7 +74,15 @@ typedef NS_OPTIONS(NSUInteger, SDWebImageOptions) {
      * By default, placeholder images are loaded while the image is loading. This flag will delay the loading
      * of the placeholder image until after the image has finished loading.
      */
-    SDWebImageDelayPlaceholder = 1 << 9
+    SDWebImageDelayPlaceholder = 1 << 9,
+    
+    /**
+     * By default, images are decoded respecting their original size. On iOS, this flag will scale down the
+     * images to a size compatible with the constrained memory of devices.
+     * If `SDWebImageProgressiveDownload` flag is set the scale down is deactivated.
+     */
+    SDWebImageScaleDownLargeImage = 1 << 10
+
 };
 
 typedef void(^SDWebImageCompletedBlock)(UIImage *image, NSError *error, SDImageCacheType cacheType);

SDWebImage/SDWebImageManager.m

@@ -134,12 +134,17 @@
             if (options & SDWebImageHandleCookies) downloaderOptions |= SDWebImageDownloaderHandleCookies;
             if (options & SDWebImageAllowInvalidSSLCertificates) downloaderOptions |= SDWebImageDownloaderAllowInvalidSSLCertificates;
             if (options & SDWebImageHighPriority) downloaderOptions |= SDWebImageDownloaderHighPriority;
+            if (options & SDWebImageScaleDownLargeImage) downloaderOptions |= SDWebImageDownloaderScaleDownLargeImage;
             if (image && options & SDWebImageRefreshCached) {
                 // force progressive off if image already cached but forced refreshing
                 downloaderOptions &= ~SDWebImageDownloaderProgressiveDownload;
                 // ignore image read from NSURLCache if image if cached but force refreshing
                 downloaderOptions |= SDWebImageDownloaderIgnoreCachedResponse;
             }
+            if (options & SDWebImageProgressiveDownload) {
+                // Progressive download deactivate scale down
+                downloaderOptions &= ~SDWebImageDownloaderScaleDownLargeImage;
+            }
             id <SDWebImageOperation> subOperation = [self.imageDownloader downloadImageWithURL:url options:downloaderOptions progress:progressBlock completed:^(UIImage *downloadedImage, NSData *data, NSError *error, BOOL finished) {
                 if (weakOperation.isCancelled) {
                     dispatch_main_sync_safe(^{