iOS渐变色逻辑

一、普通的渐变色逻辑

        var beginR : CGFloat = 0, endR : CGFloat = 0, beginG : CGFloat = 0, endG : CGFloat = 0, beginB : CGFloat = 0, endB : CGFloat = 0
        //获取RGB
        beginColor.getRed(&beginR, green: &beginG, blue: &beginB, alpha: nil)
        endColor.getRed(&endR, green: &endG, blue: &endB, alpha: nil)
        
        func byRow(direction: DrawDirection){
            var arrayRows : [Int] = []
            for row in minY..<maxY {
                arrayRows.append(row)
            }
            if direction == .up{
                arrayRows = arrayRows.reversed()
            }
            let deltaR = (endR - beginR) / CGFloat(maxY - minY)
            let deltaG = (endG - beginG) / CGFloat(maxY - minY)
            let deltaB = (endB - beginB) / CGFloat(maxY - minY)
            var offset:CGFloat = 0
            for row in arrayRows{
                let color = UIColor.init(red: beginR+deltaR*offset, green: beginG+deltaG*offset, blue: beginB+deltaB*offset, alpha: 1)
                
//                context?.setFillColor(color.cgColor)
//                context?.fill(CGRect(x: minX, y: row, width: maxX-minX, height: 1))
                context?.setStrokeColor(color.cgColor)
                context?.move(to: CGPoint(x: CGFloat(minX), y: CGFloat(row) + 0.5))   //加0.5是为了让线画的刚好在row上
                context?.addLine(to: CGPoint(x: CGFloat(maxX), y: CGFloat(row) + 0.5) )
                context?.strokePath()
                offset += 1
            }
        }

二、基于色相的渐变色逻辑

        var beginHue: CGFloat = 0, endHue: CGFloat = 0, beginBrightness:CGFloat=0, endBrightness:CGFloat = 0
        var beginSaturation:CGFloat=0, endSaturation: CGFloat = 0
                //获取色度、亮度
        beginColor.getHue(&beginHue, saturation: &beginSaturation, brightness: &beginBrightness, alpha: nil)
        endColor.getHue(&endHue, saturation: &endSaturation, brightness: &endBrightness, alpha: nil)
        func byCol(direction: DrawDirection){
            var arrayCols : [Int] = []
            for col in minX..<maxX {
                arrayCols.append(col)
            }
            if direction == .left{
                arrayCols = arrayCols.reversed()
            }
            let deltaHue = (endHue - beginHue) / CGFloat(maxX - minX)
            var offset:CGFloat = 0
            for col in arrayCols{
                let color = UIColor.init(hue: beginHue+deltaHue*offset, saturation: beginSaturation+deltaHue*offset, brightness: beginBrightness+deltaHue*offset, alpha: 1)
                
//                context?.setFillColor(color.cgColor)
//                context?.fill(CGRect(x: minX, y: row, width: maxX-minX, height: 1))
                context?.setStrokeColor(color.cgColor)
                context?.move(to: CGPoint(x: CGFloat(col) + 0.5, y: CGFloat(minY)))  //加0.5是为了让线画的刚好在row上
                context?.addLine(to: CGPoint(x:CGFloat(col) + 0.5, y: CGFloat(maxY)))
                context?.strokePath()
                offset += 1
            }
        }