How to detect Fingersize with IOS?

@fichek is right, there is no regular way to get the size of fingertips.

However, I had used a 'strange' way in my previous project to do it, and it just works ;-)

1.Tell our user to put two fingers on the screen together, the closer the better(like the two-finger scrolling gesture on Mac): enter image description here

2.Get the two CGPoints from UITouches in the touchesBegan:withEvent: method;

3.Now we have CGPoint fingertip1center and fingertip2center, so:

float fingertip_Diameter=fabsf(fingertip1center.x-fingertip2center.x);

4.The fingers are really close and we may ignore the tiny difference in width , so dX == the real width of a singel finger.

5.The width(dX) and the fingertipsize are proportional, we can simply use

float fingertip_Size=M_PI*(dX/2)*(dX/2);

or find a better algorithm to meet your needs ;-)

6.Once we got the size (actually we only care about the diameter), its easy to implement a method to optimize touching by testing various surrounded points, e.g.:

#define kTestLevelOne 5 //Testing 5 points:origin,left,right,up,down
#define kTestLevelTwo 9 //And the other 4 corners
-(BOOL)testSurroundingPoints:(CGPoint *)pt
   float prob_x[kTestLevelTwo]={0,-dX/2,dX/2,0,0,-dX/2,-dX/2,dX/2,dX/2};
   float prob_y[kTestLevelTwo]={0,0,0,dX/2,-dX/2,dX/2,-dX/2,dX/2,-dX/2};

   for(int i=0;i<kTestLevelTwo;i++)
      if([self gotItAtX:pt.x+prob_x[i] andY:pt.y+prob_y[i]]==YES)
           NSLog(@"Got It!");
           Return YES;
           //Or break; We don't need to try more points!
   return NO;

Hope these can help!

Yichao Peak Ji

Actually, there's a way to get the touch radius:

-(void)touchesBegan:(NSSet *)touches 
      withEvent:(UIEvent *)event
    UITouch *touch = [touches anyObject];
    CGFloat touchSize = [[touch valueForKey:@"pathMajorRadius"] floatValue];
    NSLog(@"touch size is %.2f", touchSize);


iOS does all sorts of finger size/angle/location calculation behind the scenes, so there is no way to detect anything but the computed location of a touch. However, that's more than enough info for you to know which part of gamepad the finger is on.

As @marcus mentioned, you should implement the touchesMoved:withEvent: method and check for touch's location to determine if it's over left/right/top/bottom/center or whatever "buttons" you want to have.