如何在Coregraphics中的路径交叉处混合两种颜色？

Question

我需要在图像视图中绘制平滑曲线时混合两种颜色，如同 - 红色和蓝色的混合应仅在两种颜色的交点处产生紫色（红色+黄色=橙色，黄色+蓝色=绿色） 。我尝试使用coregraphics的混合模式，但没有用。任何人都可以帮助我吗？

-(void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    UITouch *touch = [touches anyObject];
    self.prePreviousPoint = self.previousPoint;
    self.previousPoint = [touch previousLocationInView:self];
    CGPoint currentPoint = [touch locationInView:self];
    CGPoint mid1 = [self calculateMidPointForPoint:self.previousPoint andPoint:self.prePreviousPoint];
    CGPoint mid2 = [self calculateMidPointForPoint:currentPoint andPoint:self.previousPoint];

    UIGraphicsBeginImageContext(self.drawImageView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [currentColor setStroke];
    CGContextSetBlendMode(context, kCGBlendModeMultiply);

    CGContextSetAllowsAntialiasing(UIGraphicsGetCurrentContext(), TRUE);
    CGContextSetShouldAntialias(UIGraphicsGetCurrentContext(), TRUE);
    [self.drawImageView.image drawInRect:CGRectMake(0, 0, self.drawImageView.frame.size.width, self.drawImageView.frame.size.height)];

    CGContextMoveToPoint(context, mid1.x, mid1.y);
    //    // Use QuadCurve is the key
    CGContextAddQuadCurveToPoint(context, self.previousPoint.x, self.previousPoint.y, mid2.x, mid2.y);

    CGContextSetLineCap(context, kCGLineCapRound);

    CGContextSetLineWidth(context, self.lineWidth);

    CGContextStrokePath(context);


    self.drawImageView.image = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();
}