Detecting Special touch on the iphone

Question

I was asking myself if there are examples online which covers how you can for instance detect shapes in touch gestures.

for example a rectangle or a circle (or more complex a heart .. )

or determine the speed of swiping (over time ( like i'm swiping my iphone against 50mph ))

Answer 1

For very simple gestures (horizontal vs. vertical swipe), calculate the difference in x and y between two touches.

dy = abs(y2 - y1)
dx = abs(x2 - x1)
f = dy/dx

An f close to zero is a horizontal swipe. An f close to 1 is a diagonal swipe. And a very large f is a vertical swipe (keep in mind that dx could be zero, so the above won't yield valid results for all x and y).

If you're interested in speed, pythagoras can help. The length of the distance travelled between two touches is:

l = sqrt(dx*dx + dy*dy)

If the touches happened at times t1 and t2, the speed is:

tdiff = abs(t2 - t1)
s = l/tdiff

It's up to you to determine which value of s you interpret as fast or slow.

You can extend this approach for more complex figures, e.g. your square shape could be a horizontal/vertical/horizontal/vertical swipe with start/end points where the previous swipe stopped.

For more complex figures, it's probably better to work with an idealized shape. One could consider a polygon shape as the ideal, and check if a range of touches

1. don't have too high a distance to their closest point on the pologyon's outline, and
2. all touches follow the same direction along the polygon's outline.

You can refine things further from there.