Added the blend mode to transformer API as well

Update unit tests

SDWebImage/Core/SDImageTransformer.h

@@ -223,11 +223,14 @@ FOUNDATION_EXPORT NSString * _Nullable SDThumbnailedKeyForKey(NSString * _Nullab
  The tint color.
  */
 @property (nonatomic, strong, readonly, nonnull) UIColor *tintColor;
+/// The blend mode, defaults to `sourceAtop` if you use the old initializer
+@property (nonatomic, assign, readonly) CGBlendMode blendMode;
 
 - (nonnull instancetype)init NS_UNAVAILABLE;
 + (nonnull instancetype)new  NS_UNAVAILABLE;
 
 + (nonnull instancetype)transformerWithColor:(nonnull UIColor *)tintColor;
++ (nonnull instancetype)transformerWithColor:(nonnull UIColor *)tintColor blendMode:(CGBlendMode)blendMode;
 
 @end
 

SDWebImage/Core/SDImageTransformer.m

@@ -245,20 +245,26 @@ NSString * _Nullable SDThumbnailedKeyForKey(NSString * _Nullable key, CGSize thu
 @interface SDImageTintTransformer ()
 
 @property (nonatomic, strong, nonnull) UIColor *tintColor;
+@property (nonatomic, assign) CGBlendMode blendMode;
 
 @end
 
 @implementation SDImageTintTransformer
 
 + (instancetype)transformerWithColor:(UIColor *)tintColor {
+    return [self transformerWithColor:tintColor blendMode:kCGBlendModeSourceAtop];
+}
+
++ (instancetype)transformerWithColor:(UIColor *)tintColor blendMode:(CGBlendMode)blendMode {
     SDImageTintTransformer *transformer = [SDImageTintTransformer new];
     transformer.tintColor = tintColor;
+    transformer.blendMode = blendMode;
     
     return transformer;
 }
 
 - (NSString *)transformerKey {
-    return [NSString stringWithFormat:@"SDImageTintTransformer(%@)", self.tintColor.sd_hexString];
+    return [NSString stringWithFormat:@"SDImageTintTransformer(%@,%d)", self.tintColor.sd_hexString, self.blendMode];
 }
 
 - (UIImage *)transformedImageWithImage:(UIImage *)image forKey:(NSString *)key {

Tests/Tests/SDImageTransformerTests.m

@@ -242,6 +242,10 @@ static void SDAssertCGImageFirstComponentWhite(CGImageRef image, OSType pixelTyp
     // Check rounded corner operation not inversion the image
     UIColor *topCenterColor = [tintedImage sd_colorAtPoint:CGPointMake(150, 20)];
     expect([topCenterColor.sd_hexString isEqualToString:[UIColor blackColor].sd_hexString]).beTruthy();
+    
+    UIImage *tintedSourceInImage = [testImage sd_tintedImageWithColor:tintColor blendMode:kCGBlendModeSourceOut];
+    centerColor = [tintedSourceInImage sd_colorAtPoint:CGPointMake(150, 150)];
+    expect([centerColor.sd_hexString isEqualToString:[UIColor blackColor].sd_hexString]).beTruthy();
 }
 
 - (void)test07UIImageTransformBlurCG {
@@ -353,7 +357,7 @@ static void SDAssertCGImageFirstComponentWhite(CGImageRef image, OSType pixelTyp
                       @"SDImageRoundCornerTransformer(50.000000,18446744073709551615,1.000000,#ff000000)",
                       @"SDImageFlippingTransformer(1,1)",
                       @"SDImageCroppingTransformer({0.000000,0.000000,50.000000,50.000000})",
-                      @"SDImageTintTransformer(#00000000)",
+                      @"SDImageTintTransformer(#00000000,20)",
                       @"SDImageBlurTransformer(5.000000)",
                       @"SDImageFilterTransformer(CIColorInvert)"
                       ];