帮助正确计算atan2

Question

我需要计算直线之间的角度。我需要计算atan。所以我正在使用这样的代码

static inline CGFloat angleBetweenLinesInRadians2(CGPoint line1Start, CGPoint line1End) 
{
    CGFloat dx = 0, dy = 0;

    dx = line1End.x - line1Start.x;
    dy = line1End.y - line1Start.y;
    NSLog(@"\ndx = %f\ndy = %f", dx, dy);

    CGFloat rads = fabs(atan2(dy, dx));

    return rads;
}

但是我不能超过180度((在179度之后，178...160...150度，等等。

我需要360度旋转。我该怎么做呢？怎么了？

maby这是有帮助的：

//Tells the receiver when one or more fingers associated with an event move within a view or window.
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSArray *Touches = [touches allObjects];
    UITouch *first = [Touches objectAtIndex:0];

    CGPoint b = [first previousLocationInView:[self imgView]]; //prewious position
    CGPoint c = [first locationInView:[self imgView]];          //current position

    CGFloat rad1 = angleBetweenLinesInRadians2(center, b);  //first angel
    CGFloat rad2 = angleBetweenLinesInRadians2(center, c);  //second angel

    CGFloat radAngle = fabs(rad2 - rad1);           //angel between two lines
    if (tempCount <= gradus)
    {
        [imgView setTransform: CGAffineTransformRotate([imgView transform], radAngle)];
        tempCount += radAngle;
    }

}

Answer 1

删除fabs调用，并简单地执行以下操作：

CGFloat rads = atan2(dy, dx);

Answer 2

atan2以-180,180格式返回结果。要从0,360获得结果，请使用：

float radians = atan2(dy, dx);
if (radians < 0) {
    radians += M_PI*2.0f;
}

应该注意的是，这是典型的用-pi，pi来表达旋转，因此你可以只使用atan2的结果，而不用担心符号。

Answer 3

在Swift中使用此函数。这确保了从"fromPoint“到"toPoint”的角度在0到<360 (不包括360)之间。请注意，以下函数假定CGPointZero位于左上角。

func getAngle(fromPoint: CGPoint, toPoint: CGPoint) -> CGFloat {
    let dx: CGFloat = fromPoint.x - toPoint.x
    let dy: CGFloat = fromPoint.y - toPoint.y
    let twoPi: CGFloat = 2 * CGFloat(M_PI)
    let radians: CGFloat = (atan2(dy, -dx) + twoPi) % twoPi
    return radians * 360 / twoPi
}

对于原点位于左下角的情况

let twoPi = 2 * Float(M_PI)
let radians = (atan2(-dy, -dx) + twoPi) % twoPi
let angle = radians * 360 / twoPi