ScaleUIImage.playground

import UIKit
import XCPlayground

enum UIImageAlignment {
    case Center, Left, Top, Right, Bottom, TopLeft, BottomRight, BottomLeft, TopRight
}

enum UIImageScaleMode {
    case Fill,
    AspectFill,
    AspectFit(UIImageAlignment)
}

let trimColor = UIColor(red:1.00, green:0.79, blue:0.52, alpha:1.00)

extension UIImage {
    func imageWithSize(size: CGSize, scaleMode: UIImageScaleMode = .AspectFit(.Center), trim: Bool = false) -> UIImage {
        return scaleImage(width: size.width, height: size.height, scaleMode: scaleMode, trim: trim)
    }
    
    func scaleImage(width width: CGFloat? = nil, height: CGFloat? = nil, scaleMode: UIImageScaleMode = .AspectFit(.Center), trim: Bool = false) -> UIImage {
        let preWidthScale = width.map { $0 / size.width }
        let preHeightScale = height.map { $0 / size.height }
        var widthScale = preWidthScale ?? preHeightScale ?? 1
        var heightScale = preHeightScale ?? widthScale
        switch scaleMode {
        case .AspectFit(_):
            let scale = min(widthScale, heightScale)
            widthScale = scale
            heightScale = scale
        case .AspectFill:
            let scale = max(widthScale, heightScale)
            widthScale = scale
            heightScale = scale
        default:
            break
        }
        let newWidth = size.width * widthScale
        let newHeight = size.height * heightScale
        let canvasWidth = trim ? newWidth : (width ?? newWidth)
        let canvasHeight = trim ? newHeight : (height ?? newHeight)
        UIGraphicsBeginImageContextWithOptions(CGSizeMake(canvasWidth, canvasHeight), false, 0)
        
        // Start: remove these lines
        let context = UIGraphicsGetCurrentContext()
        CGContextSetFillColorWithColor(context, trimColor.CGColor)
        CGContextFillRect(context, CGRectMake(0, 0, width ?? newWidth, height ?? newHeight))
        // End: remove these lines
        
        var originX: CGFloat = 0
        var originY: CGFloat = 0
        switch scaleMode {
        case .AspectFit(let alignment):
            switch alignment {
            case .Center:
                originX = (canvasWidth - newWidth) / 2
                originY = (canvasHeight - newHeight) / 2
            case .Top:
                originX = (canvasWidth - newWidth) / 2
            case .Left:
                originY = (canvasHeight - newHeight) / 2
            case .Bottom:
                originX = (canvasWidth - newWidth) / 2
                originY = canvasHeight - newHeight
            case .Right:
                originX = canvasWidth - newWidth
                originY = (canvasHeight - newHeight) / 2
            case .TopLeft:
                break
            case .TopRight:
                originX = canvasWidth - newWidth
            case .BottomLeft:
                originY = canvasHeight - newHeight
            case .BottomRight:
                originX = canvasWidth - newWidth
                originY = canvasHeight - newHeight
            }
        default:
            break
        }
        self.drawInRect(CGRectMake(originX, originY, newWidth, newHeight))
        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}

let foregroundColor = UIColor(red:0.13, green:0.60, blue:0.95, alpha:1.00)
let foregroundColor2 = UIColor(red:0.56, green:0.80, blue:0.97, alpha:1.00)
let backgroundColor = UIColor(red:0.88, green:0.88, blue:0.88, alpha:1.00)

func createTestImageWithSize(size: CGSize) -> UIImage {
    UIGraphicsBeginImageContext(size)
    let context = UIGraphicsGetCurrentContext()

    CGContextSetFillColorWithColor(context, foregroundColor2.CGColor)
    CGContextFillRect(context, CGRectMake(0, 0, size.width, size.height))
    
    CGContextSetFillColorWithColor(context, foregroundColor.CGColor)
    
    let circleDiameter = min(size.width, size.height)
    let horizontalCircleCount = Int(size.width/circleDiameter)
    let verticalCircleCount = Int(size.height/circleDiameter)
    for i in 0..<horizontalCircleCount {
        for j in 0..<verticalCircleCount {
            CGContextFillEllipseInRect(context, CGRectMake(
                size.width/2 + (CGFloat(i) - CGFloat(horizontalCircleCount)/2) * circleDiameter,
                size.height/2 + (CGFloat(j) - CGFloat(verticalCircleCount)/2) * circleDiameter,
                circleDiameter, circleDiameter))
        }
    }
    
    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return image
}

func aspectFit1() {
    let view = UIImageView(frame: CGRectMake(0, 0, 128, 64))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(24, 48))
    view.image = image
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 1 (before resize)")
    view.image = image.imageWithSize(view.frame.size)
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 1 (after resize)")
}

func aspectFit2() {
    let view = UIImageView(frame: CGRectMake(0, 0, 128, 64))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(72, 16))
    view.image = image
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 2 (before resize)")
    view.image = image.imageWithSize(view.frame.size)
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 2 (after resize)")
}

func aspectFit3() {
    let view = UIImageView(frame: CGRectMake(0, 0, 64, 128))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(48, 24))
    view.image = image
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 3 (before resize)")
    view.image = image.imageWithSize(view.frame.size, scaleMode: .AspectFit(.Top))
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 3 (after resize)")
}

func aspectFit4() {
    let view = UIImageView(frame: CGRectMake(0, 0, 64, 128))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(16, 72))
    view.image = image
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 4 (before resize)")
    view.image = image.imageWithSize(view.frame.size)
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fit 4 (after resize)")
}

func aspectFill() {
    let view = UIImageView(frame: CGRectMake(0, 0, 96, 64))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(32, 48))
    view.image = image
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fill (before resize)")
    view.image = image.scaleImage(width: view.frame.size.width, scaleMode: .AspectFill)
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Aspect fill (after resize)")
}

func fill() {
    let view = UIImageView(frame: CGRectMake(0, 0, 96, 64))
    view.contentMode = .Center
    view.backgroundColor = backgroundColor
    let image = createTestImageWithSize(CGSizeMake(32, 48))
    view.image = image

    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Fill (before resize)")
    view.image = image.scaleImage(width: view.frame.size.width, height: view.frame.size.height, scaleMode: .Fill)
    XCPlaygroundPage.currentPage.captureValue(view, withIdentifier: "Fill (after resize)")
}

aspectFit1()
aspectFit2()
aspectFit3()
aspectFit4()
aspectFill()
fill()