functionality of touchscreens and user input

Question

I am an amateur (desktop) programmer but I want to get into phones. I have some ideas for apps but the touchscreen and it's inputs confuse me....

I know that touchscreens can accept multiple points of touch. For instance zooming in you take two fingers and you bring them closer.. and for zooming out you do the opposite.

Here is my problem though... I've never seen functionality with any phone app on any phone (I use windows phones and android phones) where.... the input on touch is multiple points but it doesn't begin at the same time.

For the sake of illustration I'll make an example. Suppose you have a mini browser on a phone... and it has a vertical scroll bar... and a horizontal one. What I want to do is be able to scroll down... and WHILE i am scrolling down also scroll the horizontal one so i can move the page left or right. So a few seconds after I touch the screen and begin moving the vertical scrollbar downwards or upwards... i want to use a different finger and touch the horizontal scrollbar and move it as well (at the same time).

Is this even possible? Are there certain hardware or software limitations preventing something like this?

Answer 1

Yes its possible and it depends on the phone but since most android devices and all WP7 devices got multi touch it shouldn't be a problem

Answer 2

You are mixing up gestures and touches. Gestures are touch behaviors, such as...

• Two fingers placed at the same time that grow apart from each other means zoom-in.
• Tap and hold means context popup.
• Tap and drag equals scroll.

You can cancel these gestures when your app doesn't follow these conventions. For example, Angry birds doesn't scroll if you tap and drag on a bird, but it does if you do it elsewhere on the scene.

The default state of gestures is to not detect additional touches while you are performing a gesture. if you scroll and introduce a second finger to click on a button while still holding the scroll finger, nothing will happen. I'm not sure if you can override this behavior (and I don't think it's a good idea either).

Touches, on the other hand, allow a certain amount of simultaneous touches depending on the device. When a touch is not a gesture you can start a second or n number of touches after the first one starts.

You can try this out yourself at http://raphaeljs.com/touches.html.

Now, going back to your example: it depends on how it's implemented. If you are using the OS gestures (tap and drag anywhere) then no, you can't introduce a second finger to drag horizontally, you'd use the same finger used to scroll vertically (panning with a single finger). But, if you have actual scrollbars (like those in mouse interfaces) then yes, you can implement the kind of interface you are describing.