ios - 圆几何上的点

Question

我想实现以下内容:

我在一个圆圈上有两个可触摸的对象。

如果我触摸并移动红色框中的对象，我希望左侧的对象沿着蓝色圆圈相应地移动——就好像它被一根透明的绳子拉到第一个对象后面一样。

Answer 1

这应该可以解决问题，按钮将位于 buttonFinger 的同一轴上。如果您想要一个不同的，请向 touchAngle 添加一个偏移量:

float    centerX; //Center of your Circle on X
float    centerY; //Center of your Circle on Y
float  touchAngle; //Angle of the touch
int    touchHash;
XxX    button; //Your "button" to be kept in the bluecircle
XxX    buttonFinger; //Your "button" that follow your finger

int    maxRadius; //The maximum radius: from center to the end of the blue circle
int    minRadius; //The minimum radius: from center to the beginning of the blue circle
CGRect CGRectPantone; //The CGRect of your available touch zone

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
     NSSet *allTouches = [event allTouches];
     for (UITouch *touch in allTouches)
     {
         CGPoint touchLocation = [touch locationInView:self.view];
         if (CGRectContainsPoint(CGRectPantone, touchLocation))
         {
            touchHash = [touch hash];
            buttonFinger.center = touchLocation;
         }
      }
}

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSSet *allTouches = [event allTouches];
    for (UITouch *touch in allTouches)
    {           
    if ([touch hash] == touchHash)
    {
        CGPoint touchLocation = [touch locationInView:self.view];
        if (CGRectContainsPoint(CGRectPantone, touchLocation))
        {
            buttonFinger.center = touchLocation;
            float dx = centerX - (float)touchLocation.x;
            float dy = centerY - (float)touchLocation.y;
            touchAngle = -atan2f(dx, dy)+(M_PI/2.0);

            button.center = CGPointMake(centerX-((minRadius+(maxRadius-minRadius)/2.0)*cosf(touchAngle)), centerY-((minRadius+(maxRadius-minRadius)/2.0)*sinf(touchAngle)));
        }
    }
}