Sprite Kit - Determine vector of swipe gesture to flick sprite

Question

I have a game where circular objects shoot up from the bottom of the screen and I would like to be able to swipe them to flick them in the direction of my swipe. My issue is, I don't know how to calculate the vector/direction of the swipe in order to get the circular object to get flicked in the proper direction with the proper velocity.

The static vector "(5,5)" I am using needs to be calculated by the swipe speed and direction of the swipe. Also, I need to make sure that once I make first contact with the object, it no longer happens, as to refrain from double hitting the object. Here's what I am doing currently:

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

for (UITouch *touch in touches) {
    CGPoint location = [touch locationInNode:self];

    SKNode* node = [self nodeAtPoint:location];
    [node.physicsBody applyImpulse:CGVectorMake(5, 5) atPoint:location];
}
}

Answer 1

Here's an example of how to detect a swipe gesture:

First, define instance variables to store the starting location and time .

    CGPoint start;
    NSTimeInterval startTime;

In touchesBegan, save the location/time of a touch event.

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    /* Avoid multi-touch gestures (optional) */
    if ([touches count] > 1) {
        return;
    }
    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInNode:self];
    // Save start location and time
    start = location;
    startTime = touch.timestamp;
}

Define parameters of the swipe gesture. Adjust these accordingly.

#define kMinDistance    25
#define kMinDuration    0.1
#define kMinSpeed       100
#define kMaxSpeed       500

In touchesEnded, determine if the user's gesture was a swipe by comparing the differences between starting and ending locations and time stamps.

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInNode:self];
    // Determine distance from the starting point
    CGFloat dx = location.x - start.x;
    CGFloat dy = location.y - start.y;
    CGFloat magnitude = sqrt(dx*dx+dy*dy);
    if (magnitude >= kMinDistance) {
        // Determine time difference from start of the gesture
        CGFloat dt = touch.timestamp - startTime;
        if (dt > kMinDuration) {
            // Determine gesture speed in points/sec
            CGFloat speed = magnitude / dt;
            if (speed >= kMinSpeed && speed <= kMaxSpeed) {
                // Calculate normalized direction of the swipe
                dx = dx / magnitude;
                dy = dy / magnitude;
                NSLog(@"Swipe detected with speed = %g and direction (%g, %g)",speed, dx, dy);
            }
        }
    }
}