ShadowView.swift

//
//  ShadowView.swift
//

import UIKit

@IBDesignable
class ShadowView: UIView {
    
    @IBInspectable var startAlpha: CGFloat = 90 {
        didSet {
            setNeedsDisplay()
        }
    }
    
    @IBInspectable var midAlpha: CGFloat = 45 {
        didSet {
            setNeedsDisplay()
        }
    }
    
    @IBInspectable var midPosPercent: CGFloat = 50 {
        didSet {
            setNeedsDisplay()
        }
    }
    
    @IBInspectable var endAlpha: CGFloat = 0 {
        didSet {
            setNeedsDisplay()
        }
    }
    
    override func draw(_ rect: CGRect) {
        
        guard let ctx = UIGraphicsGetCurrentContext() else {
            return
        }
        let colorSpace = CGColorSpaceCreateDeviceRGB()
        //	let scaleFactor: CGFloat = 1
        
        let rectangle = CGRect(x: 0.0, y: 0.0, width: bounds.width, height: bounds.height)
        
        ctx.saveGState()
        ctx.addRect(rectangle)
        ctx.clip()
        
        let gradientColors: [CGFloat] = [ 0, 0, 0, self.startAlpha / 100,
                                          0, 0, 0, self.midAlpha / 100,
                                          0, 0, 0, self.endAlpha / 100 ]
        
        let gradientLocations: [CGFloat] = [ 0, self.midPosPercent / 100, 0.9 ]
        
        if let gradientRef = CGGradient(colorSpace: colorSpace, colorComponents: gradientColors, locations: gradientLocations, count: 3) {
            let options: CGGradientDrawingOptions = [.drawsBeforeStartLocation, .drawsAfterEndLocation]
            ctx.drawLinearGradient(gradientRef, start: CGPoint.zero, end: CGPoint(x: 0, y: self.bounds.height), options: options)
        }
        
        //	CGContextDrawLinearGradient( ctx, gradientRef, CGPoint(x: 0, y: 0), CGPoint(x: 0, y: self.bounds.height), CGGradientDrawingOptions(CGGradientDrawingOptions.DrawsBeforeStartLocation | CGGradientDrawingOptions.DrawsAfterEndLocation) )
        
        
        ctx.restoreGState()
    }
}