Merge pull request #277 from Reflejo/upstream

Fixed CGBitmapContextCreate warnings for invalid alpha properties

SDWebImage/SDWebImageDecoder.m

@@ -13,13 +13,44 @@
 @implementation UIImage (ForceDecode)
 
 + (UIImage *)decodedImageWithImage:(UIImage *)image
-{	
+{
     CGImageRef imageRef = image.CGImage;
     CGSize imageSize = CGSizeMake(CGImageGetWidth(imageRef), CGImageGetHeight(imageRef));
     CGRect imageRect = (CGRect){.origin = CGPointZero, .size = imageSize};
 
-    CGColorSpaceRef colorSpace = CGImageGetColorSpace(imageRef);
-    CGContextRef context = CGBitmapContextCreate(NULL, imageSize.width, imageSize.height, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpace, CGImageGetBitmapInfo(imageRef));
+    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
+    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
+
+    // CGBitmapContextCreate doesn't support kCGImageAlphaNone with RGB.
+    // https://developer.apple.com/library/mac/#qa/qa1037/_index.html
+    if ((bitmapInfo & kCGBitmapAlphaInfoMask) == kCGImageAlphaNone && CGColorSpaceGetNumberOfComponents(colorSpace) > 1)
+    {
+        // Unset the old alpha info.
+        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
+        
+        // Set noneSkipFirst.
+        bitmapInfo |= kCGImageAlphaNoneSkipFirst;
+    }
+    // Some PNGs tell us they have alpha but only 3 components. Odd.
+    else if (((bitmapInfo & kCGBitmapAlphaInfoMask) & (kCGImageAlphaFirst | kCGImageAlphaLast)) != 0
+             && CGColorSpaceGetNumberOfComponents(colorSpace) == 3)
+    {
+        // Unset the old alpha info.
+        bitmapInfo &= ~kCGBitmapAlphaInfoMask;
+        
+        // Set noneSkipFirst.
+        bitmapInfo |= kCGImageAlphaPremultipliedFirst;
+    }
+
+    // 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);
+    CGColorSpaceRelease(colorSpace);
 
     // If failed, return undecompressed image
     if (!context) return image;