iOS blend mode multiply - ios

Question

I'm looking for a solution to create this red box:
It is using a color filter 'Multiply'. Currently I have found this information:
https://developer.apple.com/library/mac/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_images/dq_images.html
But how can I use something like the multiply effect on a UIView or isn't this possible?
So that the background is a UIImageView and the red box is a UIView with the multiply effect.

Answer 1

This Swift extension did the trick for me.
extension UIImage {
//creates a static image with a color of the requested size
static func fromColor(color: UIColor, size: CGSize) -> UIImage {
let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
CGContextSetFillColorWithColor(context, color.CGColor)
CGContextFillRect(context, rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img
}
func blendWithColorAndRect(blendMode: CGBlendMode, color: UIColor, rect: CGRect) -> UIImage {
let imageColor = UIImage.fromColor(color, size:self.size)
let rectImage = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
UIGraphicsBeginImageContextWithOptions(self.size, true, 0)
let context = UIGraphicsGetCurrentContext()
// fill the background with white so that translucent colors get lighter
CGContextSetFillColorWithColor(context, UIColor.whiteColor().CGColor)
CGContextFillRect(context, rectImage)
self.drawInRect(rectImage, blendMode: .Normal, alpha: 1)
imageColor.drawInRect(rect, blendMode: blendMode, alpha: 1)
// grab the finished image and return it
let result = UIGraphicsGetImageFromCurrentImageContext()
//self.backgroundImageView.image = result
UIGraphicsEndImageContext()
return result
}
}
Swift 3:
static func fromColor(color: UIColor, size: CGSize) -> UIImage {
let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
context!.setFillColor(color.cgColor)
context!.fill(rect)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}
func blendWithColorAndRect(blendMode: CGBlendMode, color: UIColor, rect: CGRect) -> UIImage {
let imageColor = UIImage.fromColor(color: color, size:self.size)
let rectImage = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
UIGraphicsBeginImageContextWithOptions(self.size, true, 0)
let context = UIGraphicsGetCurrentContext()
// fill the background with white so that translucent colors get lighter
context!.setFillColor(UIColor.white.cgColor)
context!.fill(rectImage)
self.draw(in: rectImage, blendMode: .normal, alpha: 1)
imageColor.draw(in: rect, blendMode: blendMode, alpha: 1)
// grab the finished image and return it
let result = UIGraphicsGetImageFromCurrentImageContext()
//self.backgroundImageView.image = result
UIGraphicsEndImageContext()
return result!
}
But only works for images, I would like to work for videos too :|

Answer 2

I expanded #pegpeg solution and added a gradient overlay to the image instead of a single color
Swift 4:
static func fromGradient(colors: [UIColor], locations: [CGFloat], horizontal: Bool, size: CGSize) -> UIImage {
let rect = CGRect(x: 0, y: 0, width: size.width, height: size.height)
UIGraphicsBeginImageContext(rect.size)
let context = UIGraphicsGetCurrentContext()
let colorSpace = CGColorSpaceCreateDeviceRGB()
let cgColors = colors.map {$0.cgColor} as CFArray
let grad = CGGradient(colorsSpace: colorSpace, colors: cgColors , locations: locations)
let startPoint = CGPoint(x: 0, y: 0)
let endPoint = horizontal ? CGPoint(x: size.width, y: 0) : CGPoint(x: 0, y: size.height)
context?.drawLinearGradient(grad!, start: startPoint, end: endPoint, options: .drawsAfterEndLocation)
let img = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
return img!
}
func blendWithGradientAndRect(blendMode: CGBlendMode, colors: [UIColor], locations: [CGFloat], horizontal: Bool = false, alpha: CGFloat = 1.0, rect: CGRect) -> UIImage {
let imageColor = UIImage.fromGradient(colors: colors, locations: locations, horizontal: horizontal, size: size)
let rectImage = CGRect(x: 0, y: 0, width: self.size.width, height: self.size.height)
UIGraphicsBeginImageContextWithOptions(self.size, true, 0)
let context = UIGraphicsGetCurrentContext()
// fill the background with white so that translucent colors get lighter
context!.setFillColor(UIColor.white.cgColor)
context!.fill(rectImage)
self.draw(in: rectImage, blendMode: .normal, alpha: 1)
imageColor.draw(in: rect, blendMode: blendMode, alpha: alpha)
// grab the finished image and return it
let result = UIGraphicsGetImageFromCurrentImageContext()
//self.backgroundImageView.image = result
UIGraphicsEndImageContext()
return result!
}
the colors array should be of the same length of the locations array, example:
let newImage = image.blendWithGradientAndRect(blendMode: .multiply,
colors: [.red, .white],
locations: [0,1],
horizontal: true,
alpha: 0.8,
rect: imageRect)