IOS中使用CGContext画图填充渐变颜色图层

-(void)fillColor

{ //pointArr中存放的是每个点的CGPoint,自右向左画

    //填充颜色

    float alpha = 0;

    //计算分层透明度

    

    

    CGContextRef gc = UIGraphicsGetCurrentContext();

    

    //创建CGMutablePathRef

    CGMutablePathRef path = CGPathCreateMutable();

        if ([pointArr count]>1) {

            for (int j =1; j<[pointArr count]; j++) {

                CGPoint point = [pointArr[j-1] CGPointValue];

                CGPathMoveToPoint(path, NULL,point.x, point.y);//右上角开始画

                CGContextMoveToPoint(gc,  point.x, point.y);

                CGPathAddLineToPoint(path, NULL, point.x, SELF_HEIGHT -