Improved and generalized image thumbnail decoding logic

Reviewed By: jspahrsummers

Differential Revision: D2631934

fb-gh-sync-id: 3ddea328dcb0fc84b9d7b20708324f0b515f1b7f

Libraries/CameraRoll/RCTAssetsLibraryImageLoader.m

@@ -21,7 +21,6 @@
 #import "RCTUtils.h"
 
 static dispatch_queue_t RCTAssetsLibraryImageLoaderQueue(void);
-static UIImage *RCTScaledImageForAsset(ALAssetRepresentation *representation, CGSize size, CGFloat scale, UIViewContentMode resizeMode, NSError **error);
 
 @implementation RCTAssetsLibraryImageLoader
 {
@@ -99,14 +98,30 @@ RCT_EXPORT_MODULE()
 
 #endif
 
-          UIImage *image;
+          UIImage *image = nil;
           NSError *error = nil;
           if (useMaximumSize) {
+
             image = [UIImage imageWithCGImage:representation.fullResolutionImage
                                         scale:scale
                                   orientation:(UIImageOrientation)representation.orientation];
           } else {
-            image = RCTScaledImageForAsset(representation, size, scale, resizeMode, &error);
+
+            NSUInteger length = (NSUInteger)representation.size;
+            uint8_t *buffer = (uint8_t *)malloc((size_t)length);
+            if ([representation getBytes:buffer
+                                fromOffset:0
+                                    length:length
+                                      error:&error]) {
+
+              NSData *data = [[NSData alloc] initWithBytesNoCopy:buffer
+                                                          length:length
+                                                    freeWhenDone:YES];
+
+              image = RCTDecodeImageWithData(data, size, scale, resizeMode);
+            } else {
+              free(buffer);
+            }
           }
 
           completionHandler(error, image);
@@ -151,48 +166,3 @@ static dispatch_queue_t RCTAssetsLibraryImageLoaderQueue(void)
 
   return queue;
 }
-
-// Why use a custom scaling method? Greater efficiency, reduced memory overhead:
-// http://www.mindsea.com/2012/12/downscaling-huge-alassets-without-fear-of-sigkill
-
-static UIImage *RCTScaledImageForAsset(ALAssetRepresentation *representation,
-                                       CGSize size,
-                                       CGFloat scale,
-                                       UIViewContentMode resizeMode,
-                                       NSError **error)
-{
-  NSUInteger length = (NSUInteger)representation.size;
-  NSMutableData *data = [NSMutableData dataWithLength:length];
-  if (![representation getBytes:data.mutableBytes
-                     fromOffset:0
-                         length:length
-                          error:error]) {
-    return nil;
-  }
-
-  CGSize sourceSize = representation.dimensions;
-  CGSize targetSize = RCTTargetSize(sourceSize, representation.scale,
-                                    size, scale, resizeMode, NO);
-
-  NSDictionary *options = @{
-    (id)kCGImageSourceShouldAllowFloat: @YES,
-    (id)kCGImageSourceCreateThumbnailWithTransform: @YES,
-    (id)kCGImageSourceCreateThumbnailFromImageAlways: @YES,
-    (id)kCGImageSourceThumbnailMaxPixelSize: @(MAX(targetSize.width, targetSize.height) * scale)
-  };
-
-  CGImageSourceRef sourceRef = CGImageSourceCreateWithData((__bridge CFDataRef)data, nil);
-  CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(sourceRef, 0, (__bridge CFDictionaryRef)options);
-  if (sourceRef) {
-    CFRelease(sourceRef);
-  }
-
-  if (imageRef) {
-    UIImage *image = [UIImage imageWithCGImage:imageRef scale:scale
-                                   orientation:UIImageOrientationUp];
-    CGImageRelease(imageRef);
-    return image;
-  }
-
-  return nil;
-}

Libraries/Image/RCTImageUtils.h

@@ -40,3 +40,20 @@ RCT_EXTERN CGSize RCTTargetSize(CGSize sourceSize, CGFloat sourceScale,
 RCT_EXTERN BOOL RCTUpscalingRequired(CGSize sourceSize, CGFloat sourceScale,
                                      CGSize destSize, CGFloat destScale,
                                      UIViewContentMode resizeMode);
+/**
+ * This function takes a source size and scale and returns the size in pixels.
+ * Note that the pixel width/height is rounded up to the nearest integral size.
+ */
+RCT_EXTERN CGSize RCTSizeInPixels(CGSize pointSize, CGFloat scale);
+
+/**
+ * This function takes the source data for an image and decodes it at the
+ * specified size. If the original image is smaller than the destination size,
+ * the resultant image's scale will be decreased to compensate, so the
+ * width/height of the returned image is guaranteed to be >= destSize.
+ * Pass a destSize of CGSizeZero to decode the image at its original size.
+ */
+RCT_EXTERN UIImage *RCTDecodeImageWithData(NSData *data,
+                                           CGSize destSize,
+                                           CGFloat destScale,
+                                           UIViewContentMode resizeMode);

Libraries/Image/RCTImageUtils.m

@@ -9,6 +9,9 @@
 
 #import "RCTImageUtils.h"
 
+#import <ImageIO/ImageIO.h>
+#import <tgmath.h>
+
 #import "RCTLog.h"
 
 static CGFloat RCTCeilValue(CGFloat value, CGFloat scale)
@@ -193,3 +196,69 @@ BOOL RCTUpscalingRequired(CGSize sourceSize, CGFloat sourceScale,
       return NO;
   }
 }
+
+RCT_EXTERN CGSize RCTSizeInPixels(CGSize pointSize, CGFloat scale)
+{
+  return (CGSize){
+    ceil(pointSize.width * scale),
+    ceil(pointSize.height * scale),
+  };
+}
+
+RCT_EXTERN UIImage *RCTDecodeImageWithData(NSData *data,
+                                           CGSize destSize,
+                                           CGFloat destScale,
+                                           UIViewContentMode resizeMode)
+{
+  CGImageSourceRef sourceRef = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);
+  if (!sourceRef) {
+    return nil;
+  }
+
+  // get original image size
+  CGSize sourceSize;
+  CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(sourceRef, 0, NULL);
+  if (!imageProperties) {
+    CFRelease(sourceRef);
+    return nil;
+  }
+  NSNumber *width = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
+  NSNumber *height = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
+  sourceSize = (CGSize){width.doubleValue, height.doubleValue};
+  CFRelease(imageProperties);
+
+  if (CGSizeEqualToSize(destSize, CGSizeZero)) {
+    destSize = sourceSize;
+  }
+
+  // calculate target size
+  CGSize targetSize = RCTTargetSize(sourceSize, 1, destSize, destScale, resizeMode, YES);
+  CGSize targetPixelSize = RCTSizeInPixels(targetSize, destScale);
+  CGFloat maxPixelSize = fmax(fmin(sourceSize.width, targetPixelSize.width),
+                              fmin(sourceSize.height, targetPixelSize.height));
+
+  NSDictionary *options = @{
+    (id)kCGImageSourceShouldAllowFloat: @YES,
+    (id)kCGImageSourceCreateThumbnailWithTransform: @YES,
+    (id)kCGImageSourceCreateThumbnailFromImageAlways: @YES,
+    (id)kCGImageSourceThumbnailMaxPixelSize: @(maxPixelSize),
+  };
+
+  // get thumbnail
+  CGImageRef imageRef = CGImageSourceCreateThumbnailAtIndex(sourceRef, 0, (__bridge CFDictionaryRef)options);
+  CFRelease(sourceRef);
+  if (!imageRef) {
+    return nil;
+  }
+
+  //adjust scale
+  size_t actualWidth = CGImageGetWidth(imageRef);
+  CGFloat scale = actualWidth / targetSize.width;
+
+  // return image
+  UIImage *image = [UIImage imageWithCGImage:imageRef
+                                       scale:scale
+                                 orientation:UIImageOrientationUp];
+  CGImageRelease(imageRef);
+  return image;
+}