iOS 中根据线条的角度不同随机产生颜色

- (UIColor *)lineColor
{
CGFloat xDs = self.end.x - self.begin.x;
CGFloat yDs = self.end.y - self.begin.y;

CGFloat angle = atan2f(xDs,yDs);
//atan的范围是（-M_PI/2,+M_PI/2）
//atan2f的值域为（-M_PI,+M_PI）,经过先加M_PI 再除M_PI*2 得到范围（0,1）进而符合colorWithHue的范围
CGFloat cValue = (angle +M_PI )/(M_PI * 2);

UIColor *color = [UIColor colorWithHue:cValue saturation:1.0 brightness:1.0 alpha:1.0];

return color;

}