如何让用户在iOS中绘制重叠的颜色？

Question

我正在制作drawing application like this，但我有一个问题。问题是，当我用一种颜色绘制一条线然后用另一种颜色绘制一条线时，它会给出两条线相交的颜色组合。

- (void)drawRect:(CGRect)rect
{

    [curImage drawAtPoint:CGPointMake(0, 0)];
    CGPoint mid1 = midPoint(previousPoint1, previousPoint2); 
    CGPoint mid2 = midPoint(currentPoint, previousPoint1);

    CGContextRef context = UIGraphicsGetCurrentContext(); 

    [self.layer renderInContext:context];

    CGContextMoveToPoint(context, mid1.x, mid1.y);
    CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); 
    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, self.lineWidth);
    CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);

    CGContextStrokePath(context);

    [super drawRect:rect];

    [curImage release];

}

项目的其余部分可用on GitHub。

Answer 1

也许看看混合模式。

https://developer.apple.com/library/mac/#documentation/graphicsimaging/Reference/CGContext/Reference/reference.html#//apple_ref/c/tdef/CGBlendMode